Forums/Z31P/z31-repairs-forums engine-mechanical/Lets try again… hard to diagnose misfire/hard start issue on an 85T
Imported from Z31Performance.com Forums{{#if:Tomakze| — original post by Tomakze}}{{#if:2013-06-23 22:55:53|, posted 2013-06-23 22:55:53}}{{#if:23| · 23 post{{#ifeq:23|1||s}}}}{{#if:/Z31performance_archive/forum/z31-repairs-forums/engine-mechanical/21882-lets-try-again-hard-to-diagnose-misfire-hard-start-issue-on-an-85t.html|
Local archive: view archived thread on dev.z31library.com}}
Tomakze: (2013-06-23 22:55:53)
Many of you know I've been fighting to get my 85T to run properly ever since I bought it 7 years ago. It was so frustrating, I gave up on it for 6 of those years. Well, now I truly need this car to work, so I'm trying again. The issue: Always hard to start after it sits for a while, and stalls and misfires for a while until it gets going. It used to work well after I got it into boost and warmed up a bit, but after I swapped trannys (Auto to manual) now it misfires 24/7, although I believe there are two separate problems at this point.
What I've done to fix it, or try, anyway:
1) Swapped FPR. Both used, neither leak. No change.
2) Cleaned MAF. No change.
3) Replaced CHTS and subharness. Everything improved, but problem persists.
4) Tune up including NGK plugs, new wires, cap and rotor. No change.
5) Swapped trannies from Auto to manual, caused a separate, more severe problem.
6) Swapped ECUs. 85 auto to 84 manual. Idle dropped to the point where it won't stay running.
7) Replaced all vacuum lines except the ones on the turbo, and the breathers. Subtle improvement.
8) New timing belt, water pump, and tensioner. Improved, but same problem present. Timing IS correct.
9) PRW-2 swap. Smoother idle, faster response, problem persists.
10) Deleted fuel pressure solenoid (FPR vac line straight to the manifold) no change.
11) Installed Walbro fuel pump and new fuel filter, no change.
There's more, I'm sure, but I can't remember. As you can tell, I've poured hours and hours into this repair, with very little progress, and now I've even managed to regress a bit.
First and foremost, I need it to run smooth again once warmed up. It always used to, until I converted to a manual transmission. It misfires constantly now, and is generally undrivable.
This HAS to be related to the tranny swap in some way, as it changed as soon as the new tranny went in. Here is what I think could have caused it:
During the install, we broke the exhaust studs on the downpipe (as does everyone else it seems). We did everything we could to remove them, but only managed to remove one. We decided to drill the other two out, but they broke our drill bits! At that point, I gave up, and took it and a spare downpipe I had from an 84T to an exhaust shop to have it repaired. He said the 84T downpipe was in better shape, and replaced the studs in that, and I bolted it up to my '85. It looked identical other than it didn't have a heat shield on top, and bolted up perfectly. The guy who fixed it also said to use copper sealant to re-install it, and so I did. I'm worried this has created some kind of problem now, because it was the only change we made to the engine, other than adjusting the TPS according to the Haynes manual.
Any help would be SO appreciated, I've been chasing my tail for a while on this one, and I'm tired. My daily driver is also dying, and I need the Z to become my primary transportation ASAP. This is all that is holding me up now.
G-E: (2013-06-23 23:29:20)
You should read the fsm and diagnose your actual engine to ecu harness before going crazy replacing parts
You can start the car with none of the transmission sensors, o2/fts/chts or afm sensor attached, for testing you can loop or plug all the vacuum lines too and just run one from the plenum directly to fpr
Bad/leaky exhaust gaskets might cause rough running but shouldn't prevent you starting
You need to narrow this down to a hot start problem or a fueling/ignition problem, your frustration has blinded you
Axel kain: (2013-06-24 04:01:27)
I run mine on MAF, CHTS, and CAS (distributor). VERIFY - - that plug wires for 4 and 6 are not crossed at the distributor cap. it happens. make sure the ECU you have IS BY NUMBERS an 84T ECU! I would also look into a spare working MAF as a just in case part to test with, as I have yet to hear of "cleaning" one actually working. they clean themselves. its also wise to have a spare regardless. I would highly advise running ECU codes to see what turns up.
the changes you have made - trans, and elbow change, would have no bearing on how it runs, unless there is an issue affecting the o2 sensor - unplug and see if it changes situation.
jaqattack02: (2013-06-24 13:44:36)
These things. Especially since you said issues with idle happened when you put in the new ECU. If you aren't sure on the ECU, post up a picture of the numbers on it so we can look it up.
Also, in addition to a known good MAF, I'd also try swapping in a known good distributor. Could be the CAS on the way out.
Tomakze: (2013-06-24 16:28:55)
It runs the same with both ECUs, but since the manual ECU has a lower idle, it stalls more easily. The ECU came from my parts car, so I know it is a genuine 84T ECU.
When I swapped the downpipe, I left the other O2 sensor in it (From the 84), and I don't know of it's condition. Would a bad O2 sensor cause this? If so, I think that may be my answer. I never thought an O2 sensor would have such a profound effect on the way a car runs.
I also have a spare distributor laying around that I may try out, I don't know if it is good, but it probably is. The car it came from was the same car as the ECU, and it was junked because of a hole in the side of the block. Everything I've ever removed from it so far has worked perfectly. (Only 96k on the odo!)
I have 2 MAFs laying around, but both are bad unfortunately. I haven't found a good spare yet, though I've obviously tried.
Plug wires weren't touched when this happened, so the order should still be correct.
les_joey_paul: (2013-06-25 00:14:03)
Just to clarify…
Plug wire for cyl #4 should be plugged into the #4 spot on the dizzy cap, correct?
Even though it doesn't follow the pattern of 1, 3, 5 that's on the opposite side?
Axel kain: (2013-06-25 02:56:34)
concerning the low idle, be sure the TPS is adjusted correctly too.
Tomakze: (2013-06-25 17:33:57)
I'd still like to know about the O2 sensor. Would a bad O2 cause this? I'm going to work on it today, and try to get it going again.
Edit: I realized I missed something when reading. You said to unplug the O2 sensor? I'll try that and see what happens, and report back.
GuerreroZ: (2013-06-25 17:55:12)
I been struggling with mine too, i replaced multiple things as well, almost simmilar to what you done to your car, those ur car have a air leak sound around the Idle stop selenoid and the Idle control valve,(IACV) mine did, so finally ended ordering those parts i believe they will come in i let you know how it does.
Tomakze: (2013-06-25 21:44:32)
Okay, I have had some time to play with it, and have made progress! It dawned on me that my brother has an '86 NA with a manual tranny that runs like new, so we used parts from it to do some testing. When we swapped the TPS, the car suddenly ran 1000x better, before spending any time getting it adjusted perfectly. It still doesn't run perfectly, but it answered at least one question. I ordered a new one from Rockauto. It should be in next week. I also ordered new plug wires, a new ignition coil, and an o2 sensor. I want this car in top running order, I'm tired of fussing with it!
I know it looks like I'm just throwing parts at it, and I am. I had always planned on replacing most of this stuff anyway though, as I wanted mostly new parts in this car so it is trustworthy. Once I get these parts in, I'll let you guys know what happens.
jaqattack02: (2013-06-26 13:20:36)
Did you ever try just unplugging the O2 sensor to see if it makes a difference. It really isn't needed anyway.
NissanEgg: (2013-06-26 16:27:19)
Sounds like you may harness issues.
Tomakze: (2013-06-27 05:58:02)
I did unplug the O2, and when I did, it ran worse, if anything. I ordered a new one just in case though. The O2 in there is crazy old, so who knows what condition it is in or how long it will last if it does work. Cheap insurance.
Gregmatic: (2013-06-27 13:25:22)
I see no mention of you checking/changing/cleaning the injectors. That would also be something that I'd look into and would be willing to bet it'll clear up many of your remaining issues…
NissanEgg: (2013-06-27 13:29:49)
You need to ohm out each injector. Should be about 2-4ohms for your year car. Any that read below 2ohms or more than 5ohms are bad, including OFL or infinity.
Tomakze: (2013-06-27 22:06:44)
I did do an injection cleaning service (Through a vacuum line) and ran plenty of injector cleaner through it, but that is very solid advise, that I will follow. Thank you both!
Tomakze: (2013-07-03 06:36:45)
Okay, I got some stuff done today! I installed the new plug wires, (#4 and 6 SUCK to get to!) while making sure they all went to the correct places, installed/adjusted the new TPS (It helped), installed the new coil, and then the new Bosch O2 sensor. The car definitely runs noticeably better. The misfire at cruising went away almost completely, and was diminished under acceleration. I can actually drive it some now, I think. This does not mean fixed, though. It misfires especially while under boost, and just afterwards, then smooths out. Vacuum pressure at idle is about 15inhg. After revving it, it dips down to 20, then comes up to 15… vacuum leak?
Tomorrow, I will test the injectors, swap the distributor, and fix the exhaust leak. Here's where I need your help though:
1)I noticed the wastegate has an adjustment on the rod. What does this do/how do I adjust it? Would that contribute to my issues, since the downpipe and flapper valve is different?
2) I was also wondering if I need to use different vacuum lines for the turbo, due to the added heat in that area. I have silicone lines left over from when I redid all the other vacuum lines in the car, would those still work?
3) Lastly, I want to replace the rubber hose between the charge pipe and the intake manifold. What size is it? I was planning on ordering a reinforced one from the same site I bought my lines from.
The only other thing I was going to do is to replace both crankcase ventilation hoses, but I'm guessing I can only get those from the dealer. Mine are hard as a rock, and probably leak.
Tomakze: (2013-07-03 21:36:52)
Drove a little longer today. Definitely still has the misfire, but it isn't as pronounced. It also starts better than it used to. I still need this fixed though… I have one month to get it through emissions!
Axel kain: (2013-07-04 05:14:16)
the throttle body coupler should be 2 3/4"
have you verified ignition timing since all the recent updates?
what NGK plugs are you actually running? also - at what gap?
the vacuum doing that is negligible. as it makes sense going that low on closed throttle, and regaining for idle (the IAC opens).
I'd advise against messing with the wastegate rod.
Tomakze: (2013-07-04 06:53:19)
Drove it about 40 miles or so, under different conditions today. It definitely runs much better when it's hot. All that progress I seemed to have made must have been at least partially climate related. Engine misfires under load, for sure, although it isn't consistent. Occasionally, it pulls smoothly under boost, most of the time though, it coughs and hacks. At lower speeds, while cruising, it runs smooth as silk.
In response to Axel kain:
I checked the timing again today, and it is perfect. Of course, that assumes my timing light is accurate. I may take it somewhere and borrow a timing light to verify.
I'm running NGK v-power plugs, set to .44 and brand new NGK wires. The plugs haven't changed from when it was running well.
I will still replace those lines since I'm sure it needs them anyway, but thank you!
My concern is we effectively did mess with that adjustment rod when we swapped downpipes. We also added thickness by using copper sealant. Do you still think that is okay?
I had another thought today… When we did the tranny swap, I'm not sure if we hooked up a ground cable… could that cause this? I may have installed one, but it was a crazy day, and may have forgotten. The old tranny had a somewhat small cable towards the back of the tranny. I know this has to be related to the tranny swap in some way, since the misfiring appeared immediately after we did it.
My only other thought was that I still have a small exhaust leak before the cat, and I don't know how that would effect how the car ran, but someone suggested it to me as a possible cause. (Due to less backpressure… sounds unlikely to me…)
Thanks again, I need other minds on this issue, as it was suggested earlier, I think my frustration is getting the better of me.
Tomakze: (2013-07-06 22:47:29)
I found a video on how to adjust the tension on an internal wastegate rod. I may try this… It's free, and will put my mind at ease.
I'd still like to know if the silicone vac lines will work on the wastegate, or if I need something higher temp. If someone can answer that, I'd appreciate it!
I also have more info that may help diagnose this. I've driven it more, and noticed the car does NOT like it when I engine brake. That is, when I downshift and put the engine under load. As soon as I come to a stop, it stalls, and won't run right for a short time after restarting. I can pedal it to keep it going, but it misfires BADLY and won't respond to throttle. If I press the clutch in, and let it idle down normally, it idles fine, and aside from the constant small misfire, will run normally. This seems important to me, and may help diagnose this to someone with more experience than myself. This Tuesday I will be back to trying to repair this, and I want as many potential solutions/things to test as possible.
Tomakze: (2013-07-09 20:21:19)
I ordered that intake coupling. Thank you for the size!
I also rented a fuel pressure tester from Autozone, and will be testing it shortly. I checked the ECU codes after putting some miles down, and got a few. Vehicle Speed Sense (speedo broken), Air conditioning (Not sure why, it works perfectly), neutral safety switch (Not hooked up), and most importantly: Fuel temperature sensor. I'm now back to suspecting the pressure regulator. The pump is new, but still could be faulty. I will test the resistance on the injectors, too. It sat for so long, one or more could be plugged, but I'm not sure if that will even show up.
Tomakze: (2013-07-10 05:24:45)
PROBLEM SOLVED!!!!!
I found out why the ECU threw the "Fuel temperature sensor" code. The terminal was full of corrosion. Even though the sensor works perfectly (Well within spec) the signal never made it to the ECU. New terminal seems to have eliminated that fault. This didn't do a thing for the way the car ran, however, but did direct my attention to the FPR. After fixing the sensor, I tested the fuel pressure. I had to repair the shitty autozone rental so it would work, but once I did, it read 40psi… no matter what. Priming, idling, revving, all of it. Looks like the valve was jammed at a fixed position. No wonder it ran like shit! It was running rich most of the time, then lean under boost. Explains the awful gas mileage I was getting, too. So, I picked up a new one from Autozone for $60, put it in while still in the parking lot, and bam! Runs like a new car. It purrs at idle, revs smoothly, and the power is back!
Thanks to everyone who helped! I still have a mountain of work to do on the car, but this was my biggest stress source. It's hard to justify spending so much money on a car that barely runs, but now that it runs well, I feel better about it all. [archived image: biggrin.png]