Forums/Z31P/z31-repairs-forums engine-mechanical/Misfire and hesitation at low throttle
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designate72: (2014-02-14 03:30:32)
Alright, here is something that has been causing me trouble lately. I have a variety of new parts on my car and have managed to get it running pretty well. It finally idles decently, the idle stuff has been blocked off, new CHTS, new plugs, new wires, new dizzy cap and rotor, tried two ECUs, new silicon vacuum lines to eliminate leaks, Seafoamed everything, fresh gas, etc.
Anyways, the problem is this: The car idles fairly consistently, but at very low throttle (think below 1500 or even 1200 rpm, barely any) the car acts misses like crazy, the rpms drop and if held long enough the car will die. If I hit the throttle like normal, the car revs up fine and is fairly smooth. It is only when I barely touch the throttle that it wants to die.
Of course, I figured that this was because my TPS wasn't adjusted properly, so I broke out the multimeter. It said it was fine, but it still didn't help. Instead, I tried setting the TPS by hand, turning it with the engine on until the car dies, then turning it back just until the car idles right. This didn't work either. I have tried any number of configurations for the TPS over and over and nothing seems to help.
Perhaps I am still doing something wrong with the TPS, but I've tried enough times that now I figure I'll ask for help and see if anyone has some insight.
Butter: (2014-02-14 20:47:26)
Sounds like ignition timing to me.
designate72: (2014-02-15 00:40:29)
Time to get a timing light then? The CAS was also replaced when I initially got the car with a supposedly known good unit bought from a member here. I've tried advancing and retarding the distributor timing and that hasn't seemed to help the problem.
Butter: (2014-02-17 18:22:55)
What is the state of your PCV system? Modified? Breathers?
designate72: (2014-02-17 22:15:28)
Breather on the driver's side, standard hose to the manifold on passenger side if I am thinking of the right thing. In addition ASCO block off plates are installed and the main intake hose was replaced with one that doesn't have any holes in it from the TB to the MAF.
Butter: (2014-02-17 22:49:21)
Yeah, you're sucking in false air through that breather.
Plug the PCV line, and see if it fixes it.
designate72: (2014-02-18 00:35:04)
Plug the PCV line on the manifold or the valve cover? The manifold should be sealed, but I'll make sure. Also, now that I look at it I am reminded that there is a vacuum line coming off of the top center towards the back that I couldn't find on the vacuum line list when I redid the lines with silicon. After plugging it for a while, I just hooked it up behind the filter before the MAF, which would mean unmetered false air is getting into the intake. However, the reason I hooked it up there temporarily is that it was plugged, but the car idles much better with it getting air. And yes I did try plugging it again to see if that would help the problem now that I thought of it, and it didn't improve things. Hopefully this image makes it clear where the line comes off of:
vacline example.jpg
Does this line simply need to be attached after the MAF? I completely forgot that I hadn't found a way to hook it up correctly, so if this is the problem I'll feel pretty stupid. Still, like I said I didn't notice it in any of the vacuum line guides.
les_joey_paul: (2014-02-18 01:18:07)
That line runs to the vacuum tank, for the climate control operation.
The driver side valve cover needs to have a hose running to the intake pipe before the throttlebody
Butter: (2014-02-18 15:08:02)
Look man, if you have a breather on the valve cover, it needs to be done properly. You are definitely sucking in air through the crankcase.
-What happened to the line going to the driver's side valve cover? This needs to be capped/plugged at the intake pipe.
-On the passenger side, the PCV valve needs to be removed and plugged.
-On the opposite valve cover, that big tube needs to be replaced by:
A. A open "draft tube" leading down to the ground.
or
B. A hose going to one of those oil catch cans, then from the catch can to a spot in between the air filter and the MAF.
(I found a neat little brake booster fitting from HELP! at the parts store. It plugs right into the valve cover and even has a check valve.)
[archived image: 720214.jpg]
Also, if you have a BOV, it's probably leaking and will cause the same problems. Remove and throw away.
Attached Files
720214.jpg (3.6 KB)
designate72: (2014-02-27 05:11:53)
Look man, if you have a breather on the valve cover, it needs to be done properly. You are definitely sucking in air through the crankcase. I don't really necessarily want breathers for any reason, I installed the one because I replaced the intake tube as it had connections for the idle stuff and I though it would be better to get a sealed tube than to cap stuff.
-What happened to the line going to the driver's side valve cover? This needs to be capped/plugged at the intake pipe.
Driver's side valve cover line is gone, intake pipe was replaced when the idle stuff was deleted because I didn't want to fill in the holes. As a result, I didn't have anywhere to connect the driver's side valve cover to and put on the filter. Otherwise I would have left it connected to the intake.
[archived image: 2014-02-22180528_zps3f8a2cf9.jpg]
-On the passenger side, the PCV valve needs to be removed and plugged.
PCV Removed and plugged yesterday, and now the car idles lower and dies after letting off the gas every once in a while. Maybe I need to crack the throttle open a bit? Either way, with the PCV removed the car runs a little bit worse, only reason I can guess is that it was sucking in air and for whatever reason that happens to be helping the mixture. Obviously that isn't how it is supposed to work, but for some reason it did, sort of.
[archived image: 2014-02-22180550_zpsad816662.jpg]
-On the opposite valve cover Does this refer to the driver's side again? If it does, I will go ahead and get the check valve and hook up a draft tube, and then put the filter on the passenger's side valve cover since now that the PCV is removed there is nothing for it to go to., that big tube needs to be replaced by:
A. A open "draft tube" leading down to the ground.
or
B. A hose going to one of those oil catch cans, then from the catch can to a spot in between the air filter and the MAF.
(I found a neat little brake booster fitting from HELP! at the parts store. It plugs right into the valve cover and even has a check valve.)
[archived image: 720214.jpg]
Also, if you have a BOV, it's probably leaking and will cause the same problems. Remove and throw away. No BOV, not turbo. (yet)
Also, this is the line in question that I was talking about before:
[archived image: 2014-02-22180641_zpse01a6bb9.jpg]
Thanks for all the help, hopefully I haven't missed something obvious in these pictures that would fix it.
michaelp: (2014-02-27 17:13:15)
That last photo you posted. That line should run to the cruise control, and also be T'd off to the climate control. Your issue isn't there, while leaky climate control vacuum lines do create a vacuum leak - I've never seen them affect how the car runs, as its so minimal. Unless the large hose is leaking (to cruise control. -Is it removed?) then you may have an issue.
Do this, and report back. Unplug every sensor/actuator except CHTS, CAS, MAF and TPS. How does it run? It should run perfectly fine, as those are all that are truly needed....but the other sensors - when bad - can cause it to run poorly. Lastly, is your throttle body adjusted properly to idle now? Did you adjust the TPS after adjusting the throttle? Its only an idle switch, so if the "idle" position doesn't get contact while idling, the idle will be rough.
NissanEgg: (2014-02-27 19:37:09)
[archived image: 2014-02-22180528_zps3f8a2cf9.jpg]
That intake pipe is 50% your problem. You have a vacuum leak, and that sorry excuse for a intake pipe is leaking.
The incorrect use of the PCV breather on the valve cover is the other 50% of the problem.
designate72: (2014-02-27 19:52:49)
I was worried that might be the case, I installed that for $10 from auto zone instead of plugging the multiple holes in the stock intake. Any suggestions on what to use instead/ how best to seal the stock intake? I still have all the parts, in fact I have duplicates of most.
michaelp: (2014-02-27 20:04:56)
[archived image: 2014-02-22180528_zps3f8a2cf9.jpg]
That intake pipe is 50% your problem. You have a vacuum leak, and that sorry excuse for a intake pipe is leaking.
The incorrect use of the PCV breather on the valve cover is the other 50% of the problem.
hahaha I didn't even notice that picture. Thats horrible. Might as well use dryer vent.
Get a 2" to 2.5" 90deg coupler, a 2.5" aluminum 90deg pipe, and a 2.5" to 2.75" coupler and some t-bolt clamps. This will work until you do an intercooler setup.
Butter: (2014-02-28 15:35:14)
Throw intake "pipe" that's on there now in the trash. You can get heater hose plugs in the same aisle at the parts store to plug the fittings in the oem one (5/8"?).
With no idle controls, you will need to adjust the throttle set screw to acheive @900rpm, then recalibrate the tps to match. You must ensure all air leaks are handled first though.
Looks like you need to adjust your throttle cable too.
designate72: (2014-03-01 00:21:28)
I'll get to it this weekend. I figured as a temporary solution the cheapo duct would work, but obviously I was very wrong. Original intake pipe will go back on, as well as the line from the intake pipe to the driver's side valve cover. What about the passenger's side, though, now that I've removed the PCV? Can I just put the filter on that?
Butter: (2014-03-02 22:06:40)
If the line attaches in between the MAF and the air filter, it will be fine, but you need a catch can of some sort in between there or else MAF sensor will get fukd by the oil vapor.
designate72: (2014-03-03 02:32:09)
So the line should actually be before the MAF?
designate72: (2014-03-15 23:44:27)
Time for an update. I got out the heat gun, sealed up the original intake pipe, and put it back on. Put the breather on the passenger side, because now that the PCV is blocked off, there is nowhere for that to connect to.
[archived image: 2014-03-15192445_zps5cdafbd5.jpg]
But I still have three vacuum lines that I don't know what they should be connected to. The first is the original one I mentioned before. I'm still not clear on where it should go, as I guess the one to the cruise control has been removed, and I don't see where to connect it. Also, there are two more that I had forgotten about':
[archived image: 2014-03-15192354_zps1e899cda.jpg]
The smaller one in this picture, which is really just connected to the smallest line of the rear vacuum gallery.
[archived image: 2014-03-15192427_zpse10566ce.jpg]
Also this one, which comes of the charcoal canister.
Obviously I need to get the vacuum sorted out to know for sure, but the OEM intake pipe didn't seem to help very much. And yes, I did check that the seal was at least water tight. So right now I guess I'd just like to figure out what to do with these vacuum lines. Also, I might as well remove the cruise control at this point, as my headlight switch doesn't have the switch to activate it anyways.
les_joey_paul: (2014-03-16 05:01:38)
Looks like the small red vacuum hose was going to the egr solenoid, you should plug that one with a vacuum cap.
The bigger red vacuum tube you should run to a one way check valve, can find from the "help" section at parts store. After the check valve run that to the vacuum tank, located above the carbon canister.
The smaller black vacuum hose is it coming from a hole in the bulk head? If it is, run that to the vacuum tank, too.
That big red hose will cause a large vacuum leak, definitely enough to cause drivability issues.
les_joey_paul: (2014-03-16 05:06:29)
Also the hose you pointed out that comes off the carbon canister Is supposed to run to the little nipple on the intake pipe that's after the maf, just under the ac compressor
Also.. take the breather off all together and run a good hose to the pcv valve. With a filter on there you can let moisture and other stuff into the valve cover and eventually into your oil.
Personally I find it is best to keep it a closed system.
designate72: (2014-03-17 19:38:16)
So I went to the parts store and they didn't have a small enough check valve, I'll check a different store later. Which way should it be installed when I get it? Anyways do you mean run the big red line to the small ish rounded tank above the carbon canister? It only has two very small inlets. Also I don't have a place for the carbon canister line on my intake pipe, but I can make one if that is where it needs to go.
The situation now is that the smallest line is capped, the line from the carbon canister still doesn't go anywhere, and the big line doesn't go anywhere either. I tried capping both lines, and the car didn't seem any better than with them open. I'm thinking maybe the MAF is doing strange things, though I don't know how I would test that. But overall the car doesn't idle, and misfires throughout the RPM range whether the two lines that I am trying to locate are capped or open. It seems then that I have an additional issue to the vacuum lines, but I'm pretty lost. I will mention that though the distributor cap is brand new, it is not OEM Nissan.
designate72: (2014-03-18 15:47:33)
I've been reading a few other threads, and it sounds like perhaps I have a fuel problem, since I have replaced most of the spark related stuff.
Based on this thread: http://z31performance.com/showthread…ssue-on-an-85T and this thread http://z31performance.com/showthread…a-bigger-issue Maybe I have clogged injectors or a bad FPR. The FPR looks new and the PO claims to have replaced it, but I have an adjustable one sitting in the parts car that I think I will throw on there. If not, I wonder if I'm going to need to pull the injectors. Still, it sounds like his car still runs better than mine. Once I install the adjustable FPR, I'll post a video just in case it can help.
Butter: (2014-03-18 17:06:16)
FPR's hardly ever go bad.
Fuel supply issue wouldn't result in the problems you are describing.
This is a good page that might help, although it's for a turbo.
http://www.thumper300zx.com/z31/vacuum/vacuum.htm
When you find this thing, it's going to be something really stupid.
If you have access to an air compressor, you can do a "boost leak check" to pressurize the intake with the engine off and listen for vacuum leaks.
designate72: (2014-03-18 17:15:42)
I actually do have a small air compressor, I'll try that. Not quite sure how I would pressurize the intake, except after the TB though.
I guess I'll finish installing the adjustable FPR since I have it anyways.
I actually used that page when I bought the silicone vacuum hoses for the initial replacement. I'll go through everything again so that I can be sure I didn't miss something.
Butter: (2014-03-18 18:01:17)
You just need a 3" PVC cap. Drill hole and thread in a air coupler. Replace the MAF with this tool. Turn your air compressor regulator down to 14psi or so. Any air leaking needs to be investigated.
Don't put on that FPR, as you might complicate things more. Unless it has an on-board pres gauge. Then you can verify fuel pres. But once again, fuel delivery issue would manifest itself under heavy load, and you seem to not be having that problem. Bad injectors would have rough idle/dead cylinder. Take FPR back to the store.
designate72: (2014-03-18 18:23:52)
I replied before noticing that you had posted again. Anyways, the FPR does have a gauge, which is the other reason that I wanted to install it. But as it says below, you were right about it not being a bad FPR. It still acts the same. I'm about to go buy the PVC cap and grab my air compressor to test the vacuum.
You were right about the FPR, different one didn't help. But I at least now have an adjustable FPR.
Also something perhaps worth mentioning, I had a cap on the larger line coming off of the back of the intake manifold, and after a short test drive it was launched off. Probably just the backfire, but I though I would note it at least.
Also I'm guessing you'll be right about it being something stupid once I find it. But until I do, it is frustrating.
designate72: (2014-03-18 20:16:34)
After pressurizing the system, it actually appears that the first leak is right behind the throttle body, on the bottom somewhere. I'm going to remove the TB to reseal it and then see what happens. But it appeared to be a small leak, just a slight whistle, so I wonder if it could cause all these problems.
NissanEgg: (2014-03-18 21:59:02)
Also, with the breather on the passenger side, and the suction tube from the driver VC to the intake pipe is still a vacuum leak.
designate72: (2014-03-18 22:25:43)
So I need to put the pcv valve back on? I blocked it off based on some previous instructions. It sounds like I either need two breathers or both vc going to the OEM spot.
Also, this happened:
[archived image: IMG_20140318_183802_zpsa4522c5a.jpg]
So the throttle body removal might take a bit longer than expected. What a pain. I even had new hex bolts to install this time so that this wouldn't happen.
les_joey_paul: (2014-03-19 02:27:16)
Same thing happened when I tried to r&r my tb.. well almost.
The head of the bolt started to strip. So I just put it all back and it's been fine since then (8 months ago)
Butter: (2014-03-19 15:02:55)
I think he has the driver's side PCV vent tube plugged at the plastic lnlet pipe? Should be fine in regards to the breathers.
Also, IIRC, there is a small vacuum fitting under there by the throttle. Perhaps, it's snapped off? I even think that one is blocked by the throttle plate when it's closed. So if this is open, it would explain why you have a massive vac leak and stumble at the off-idle transistion. When you pressurize it, maybe move the throttle and see if air blasts out.
designate72: (2014-03-19 15:15:22)
With regards to the PCV line the driver's side is now hooked up normally to the intake pipe. I'm about to install a new PCV on the passenger side and hook up the OEM hose to the manifold to make sure that the breather isn't the problem.
I noticed the vacuum fitting under the throttle, and it has new silicone hose on it. But that appears to be where the air is leaking, even with the throttle closed. If not, there is air coming out somewhere along the bottom of the throttle body, even after I removed it and installed the proper gasket.
The air actually seems to come out of the bottom of the throttle body less if I open the throttle. Perhaps I'll try another throttle body after I replace the PCV valve, since I do have one around somewhere.
I'm hoping it is either the PCV or the throttle body for some weird reason, because I'm not sure what else it might be. Also, pressurized with the throttle open did not reveal any noticeable leaks down the line, at least not that I could hear, though obviously the air must be escaping somewhere.
EDIT: Turns out I don't have the extra throttle body I thought I did. Any ideas on how to know if the TB is the problem? Shouldn't be the vacuum lines to and from the TB as they are new.
Butter: (2014-03-19 16:17:05)
"With regards to the PCV line the driver's side is now hooked up normally to the intake pipe. I'm about to install a new PCV on the passenger side and hook up the OEM hose to the manifold to make sure that the breather isn't the problem."
Just take that line off and plug the port on the intake pipe. Leave the line open for now. When you open the throttle, you are probably losing all your test air out the tailpipe. Shove a rag or something in the exhaust, and listen again when you crack the throttle to test the plenum area.
les_joey_paul: (2014-03-20 01:11:05)
You can use rtv as a tb gasket, it may seal better than the oem gasket.
As for the small vacuum nipple that's on the under side of the TB, you can simply just put a vacuum cap on it. That is used for the egr solenoid, which you Have deleted.
Also are you using all oem na intake piping?
The pipe that comes after the maf has a nipple on it too
designate72: (2014-03-20 01:54:01)
les, you are right about the TB vacuum lines, I traced it and I have it capped off anyways because it went to the EGR, so I'll just cap it off wherever that line originates. You are also right about the intake piping, I thought I grabbed the 86 intake piping to reinstall but it was actually from an 88 NA, the 86 piping does have the nipple for the carbon cannister, so I'll hook that up. I guess I could take off the TB again since I'm doing other stuff anyways, and I have rtv around.
Thanks for all the advice so far everyone.
Here's what's I've noticed now. The bottom of the throttle body still appears to leak for some reason (maybe need to use the rtv to seal), but with the throttle open and the rags in the exhaust, I found what seems to be an exhaust manifold leak on the passenger's side towards the front of the car. I can't tell if the manifold is cracked or the seal is just bad, but I have new gaskets and a new manifold if necessary. Could that be part of the problem?
Also, I noticed something about the leak on top of the plenium that I've mentioned a number of times before that apparantly goes to the vacuum cannister and to to the cruise control. When it is blocked off, the car won't idle. When it is left open, which I did accidentally, the car struggles, but will eventually settle into an ok idle, with some movement. This tells me that I need to adjust the idle with the throttle body screw, because otherwise with the idle stuff deleted there's really not much air going in at idle. The other thing is, with no cruise control I'm not really sure where to route that line, because as I said the inlet and outlet on the vacuum cannister near the passenger's side headlight are very small.
Basically, I'm hoping that by adjusting the throttle screw, attaching the vacuum lines to the proper place instead of capping them, and fixing the exhaust leak will clear this up at least somewhat.
This means that I've got a few things on the list for tomorrow:
Fix the fuel line that got pinched and cut somehow. (Unrelated) Manually adjust the idle using the screw to prop open the throttle, readjust the TPS as necessary. Remove passenger's side exhaust manifold, install new gasket and/or manifold if necessary. Install 86 pipe and the line from the charcoal canister to the intake pipe so that the air is metered. Seal the upper intake pipe and leave the driver's PCV line open to air? Check and tighten all electrical connectors and grounds. Install the line coming from the top rear of the upper intake manifold somewhere?
I also have videos with the manifold line both blocked and open, which I can upload if they will be of any help.
les_joey_paul: (2014-03-20 15:11:55)
I suggest keeping the pcv tubes hooked up to the stock locations. And yes you'll have to adjust your throttle plate since you've blocked the iac.
Also make sure you have no open vacuum nipples.
As for the one that should run to the cruise control, reduce it to a 3mm hose and attach it to the small vacuum tank that's.above the carbon canister
designate72: (2014-03-20 17:25:00)
Sounds good for the one that goes to the cruise control, right now it is blocked off.
Anyways, progress:
I replaced the fuel line and adjusted the throttle to idle between 800 and 900, as well as the TPS accordingly. Blocked off the throttle body vacuum nipples and the line at the top of the manifold. Basically, cylinder 5 may have been misfiring this whole time. Now that it can finally idle without completely random misfires, I noticed that it was rhythmic. Unplugging spark plugs showed that the misfire went away when cylinder 5 was unhooked. I'm going to check the spark plug connections, but I think it is more likely to be the injector connection. Either way, I think that if I can get cylinder 5 to fire properly, that will be a major part of the solution.
designate72: (2014-03-20 18:46:10)
More observations about the misfire:
I am fairly certain that it is cylinder 5 because it the idle is rough periodically. When I unplug the cylinder 5 wire, it settles down to a smaller periodic pop that is less noticeable. The others don't do this. Basically it idles rough and then actually gets a little bit better when I unplug cylinder 5.
This tells me, then, that I have spark to the cylinder because removing spark changes something. With new plugs, wires, and distributor stuff I would hope so. That leaves fuel and compression. However, I think that I am also getting fuel, because sometimes it will just stop missing for a minute or so. Basically, this makes me think that something in the injector wiring for cylinder 5 is messed up, so I'm going to go searching. I hope the cylinder itself isn't dead because I was hoping to drive this car places over the weekend, but ultimately it wouldn't be a big deal because I have an engine to swap anyways.
I can take a video of the behavior with 5 plugged and unplugged, but I am fairly certain that is where the misfire is originating from. If I unplug the other cylinders, I can hear their misfire as well as the rougher misfire from 5, if that makes sense. Unplugging 5 seems to change the misfire from a rough "bad combustion" sort of thing to the simple pop since nothing is happening.
Butter: (2014-03-20 20:01:51)
It's common for those injector connections to corrode and turn green.
designate72: (2014-03-20 20:17:36)
I'm currently rewiring to pre campgain, but that doesn't appear to work. I may just refresh and solder the batch fire connections.
Edit: pre campgain just made it worse, but even refreshing (cutting off the ends that were being used and re stripping) the factory wiring and soldering it back left the same misfire. Could it be a clogged injector? If so can I throw the 88na injectors I have into the car?
Videos in case it helps: https://www.dropbox.com/s/27nx4he1j2…2020.49.56.mp4
https://www.dropbox.com/s/m9t6hy0fg1…2020.51.05.mp4
designate72: (2014-03-20 22:56:57)
I'm thinking that I might install the 88NA injectors just to see, I know I need the 88NA ecu which I have, though it is for an auto. Other thing is, the oxygen sensor doesn't match, so how much of a problem will that be? Either way, I can check out the original injectors when I get them out.
les_joey_paul: (2014-03-21 02:50:56)
If your o2 doesn't match it won't run right, I was using an na o2 sensor on my na2t and it ran way too rich all the time… put the turbo o2 (different part numbers) and it feels way better and no backfires at all
Just fyi
One other thing you can do is while the engine is running take a long flat head screw driver and hold it against the fuel injector connector and see if you can feel it ticking. They should all tick the same, also you should ohm check each injector itself, every injector should be within .2 of the others.
designate72: (2014-03-21 04:22:18)
Based on http://redz31.net/pages/fuel.html, it turns out I can run the 88 injectors with the 86 ECU, so the O2 sensor won't be a problem.
However, I installed the newish injectors, and there was no change. If anything, it wants to die a bit more at idle, though that may just be because it was cold. Anyways, I suppose fuel deliver isn't the problem, and spark delivery isn't the problem, so it must be vacuum somewhere I'm missing. But I still don't totally understand why that would cause a rhythmic misfire, as if one cylinder was causing the problem every time.
Anyways, I'm out of ideas and for now pretty much out of time, but if you have any suggestions I'd be glad to hear them.
Butter: (2014-03-21 05:00:57)
Make sure head temp sensor and it's short harness are in good shape. Sometimes people rig it with a resistor as a "repair".
designate72: (2014-03-21 22:12:41)
CHTS is good, subharness is also OEM new from Nissan.
ECU gives MAF and fuel temp sensor codes. I've tried another yellow max and blue maf but they didn't seem to change anything. Still, if anyone has a known working yellow sticker I'd be interested just to make sure.
designate72: (2014-03-23 13:43:19)
I think that the fuel pressure regulator might not be working, so I'm going to probably go ahead and get a new quality one just to make sure. I could put the old one on but the behavior didn't change. Anyways, just to give some more information I drove the car around for a while yesterday and the car wouldn't idle, especially if I let off the throttle while rolling, then depressed the clutch. Also, after a while it would misfire much worse when hitting the accelerator, resulting in a major loss of power. Not only that, after parking there was a good amount of smoke coming from what looked like the bottom of the passengers side exhaust manifold.
les_joey_paul: (2014-03-23 14:04:42)
Use a handheld vac Pump & make sure that the fpr hills holds vacuum
Butter: (2014-03-23 16:51:57)
Have you done a compression check yet? I must say I am impressed that you are actually going through with all this work to diagnose the problem. Most newbs would have checked out at the thought of making sure the plug gap was correct, and bought a S13. Compression check is pretty simple to do. Borrow a gauge from a parts store if you don't have one.
Just to verify, when you haul ass in this car, everything is fine and no misfire?
designate72: (2014-03-23 23:48:02)
Cylinder 1: 175
Cylinder 3: 175
Cylinder 5: 170
Cylinder 6: 175
Cylinder 4: 185
Wait for it…
Cylinder 2: About 50, and I tested it four different times.
So, I guess that's going to be the major problem then, everything else would have been secondary. I'm still a little confused because it seemed to run okay and have enough power when I would keep it in the higher RPM range, but obviously it wasn't working at its full potential. The noise may have prevented me from hearing the misfire at that point I think. I probably should have run a compression test sooner, but I didn't think it was running poorly enough to be essentially on 5 cylinders. Well, at least I know now, I should have gone ahead and done this sooner and it would have saved me a lot of effort. Still, I now have a much better idea of how everything on a VG30 works, and plenty of new stuff for the new engine. Anyways, I suppose I won't worry about finding out whether it is a ring or valve issue, because I have that other motor to put in anyways this summer. Once I pull this one, I'll may see what's wrong or I may not, since I have two spares.
Thanks for all the help everyone, it has been interesting.
I won't have time to start the swap until this summer, but I'll probably need advice on the rebuild. I have the motor that was supposedly recently rebuilt and looks like it, but I need to rebuild the T3 I have and replace whatever else I should go ahead and get to while the motor is out. But that will happen later.
As an aside, I ended up with a Z31 because I wanted an old school (cheap) Nissan and couldn't afford the S13. But now that I've had one (or three), I would buy a nice Z31 over an S13 pretty much any day. Too much ricer and drift tax, whereas the Z31 is more classy and unique. Still, it is fun every once in a while to drive my friend's 89 S13 coupe.
les_joey_paul: (2014-03-23 23:53:58)
Do a cylinder leak down test that will help guide you to the next step
designate72: (2014-03-24 02:11:24)
I'm not that worried about it, I'm probably going to swap in the spare engine that I have and then I'll think about fixing this one.
Butter: (2014-03-24 13:55:15)
Awww shucks kid. That's a bummer.
Above 1500rpm or so, that 50psi turns into over 100 because it can't leak compression fast enough at that speed. Then it will actually start running right.
cHente47: (2020-03-04 22:01:33)
I just read through this whole forum in my wine class. I can’t wait to get my 84 running proper. Till that day, I will be on the hunt doing more research. Thank you guys for all this extensive work, it is truely appreciated.