Forums/Z31P/z31-performance-upgrade-forums engine-management/CHTS - problem or symptom or bad JWT ECU?
Imported from Z31Performance.com Forums{{#if:Kingman| — original post by Kingman}}{{#if:2012-10-22 22:04:13|, posted 2012-10-22 22:04:13}}{{#if:22| · 22 post{{#ifeq:22|1||s}}}}{{#if:/Z31performance_archive/forum/z31-performance-upgrade-forums/engine-management/19609-chts-problem-or-symptom-or-bad-jwt-ecu.html|
Local archive: view archived thread on dev.z31library.com}}
Kingman: (2012-10-22 22:04:13)
Been battling a running rough, low/sporadic idle, stumbling, running rich, lack of power, sometimes running perfect issue. '88 ECU with JWT 450 tune, MB "420cc" injectors, Cobra MAF, Walbro 255 pump. No vacuum leaks. Stock FPR with 174K miles. No EGR valve. No O2 sensor. Perfect compression. Good fuel pressure. Been through 3 IACVs. Squeaky clean MAF. Recently, and sometimes, it'll drive fine until 3.5k+ RPMs were it suddenly starts missing/sputtering under load and boost (idiotic but more boost clears it up). But that's relatively new and sometimes it doesn't do it.
I replaced the CHTS with a factory Nissan sensor a few weeks back and it didn't change much. Sub harness has zero resistance and neither does the wiring harness to the ECU. It fires right up in the morning first crank of the starter. As it warms up it starts running like crap - sometimes worse than others. Today it started running real rough and sounded pretty bad. When I unplug the CHTS the idle jumps up and it smooths out. But it does it MOST OF THE TIME. Sometimes when I unplug it, while it's running like crap, the idle will jump up and the engine smooths out but when I plug it back in it'll stay the same for a bit then slowly start running worse. Most of the time when I plug it back in it instantly runs like crap again. Sometimes when coming to a stop the idle will be at 1K where I set it, smooth as silk and others it will be down to about 600 running real rough. When it comes to idle at 1K like it should, after 15 or so seconds it simply starts running rough and the idle drops. It's actually becoming a pretty severe problem. I made a video. I'm waiting for a new CHTS to come in so I can swap them out but it seems like there's an underlying issue and the CHTS is the symptom of something elsewhere not jiving with it. It doesn't even do the proper "rev-up" when you start it. Usually sputters to life but not as bad as in the video. I took the video today since it's running worse than usual.
http://s273.photobucket.com/albums/jj20 … 737337.mp4
Close to being at my wits end. Ideally I'd like to throw an entire new harness at it with a new ECU but JWTs are hard to come by and they aren't cheap. Don't have the money for Nistune so I'm kinda stuck.
Kingman: (2012-10-23 01:00:47)
Re: CHTS - problem or symptom?
After I posted this I think my Cobra either failed or went way out of whack. It gave me a real good hiccup then started running super rich and consistently idling at about 500RPM. Driving it falls on it's face yet boost builds.
Does anyone know off hand the values of the MAF at idle? I know it's a 2-7V system but that's about it.
Scratch Cobra MAF. It's interchanged as '89-'93 5.0s, 3.8L Taurus, and a few Mercuries. Just the Cobra MAF housing.
Careless: (2012-10-23 05:42:55)
Re: CHTS - problem or symptom?
what about the air regulator on the pass side? did u change to a square style rebuildable one?
what about the ecu. did you try without the shitty JWT ?
Kingman: (2012-10-23 06:05:41)
Re: CHTS - problem or symptom?
I did, but I blocked it off and nope I haven't done that quite yet.
Kingman: (2012-10-23 19:45:20)
Re: CHTS - problem or symptom?
Called up Jim Wolf, the MAF in my car isn't even the right one lol. Part number needs to be an F1SF not F1ZF from a '93 Cobra only. Sheitt. But it used to run fine with the smaller Taurus MAF so I'm going to yank one from a yard and see what happens.
Kingman: (2012-10-24 05:25:12)
Re: CHTS - problem or symptom?
New MAF didn't change a thang.
nismopu: (2012-10-24 05:39:55)
Re: CHTS - problem or symptom?
Did you find out what your voltage readings are?
Kingman: (2012-10-24 06:15:00)
Re: CHTS - problem or symptom?
No he didn't give them to me. Said there's no accurate way of testing it on the car? I thought that was a little weird. When I read him the numbers off my MAF the first thing he said was "that is definitely not the right one for your ECU."
But you rode in it, thing ran pretty damn good!
Check this shit out, this is under half throttle:
http://s273.photobucket.com/albums/jj20 … 513478.mp4
It still runs a lot better with the CHTS unplugged. Chris got me a new one so we'll see but I don't think it's going to change anything. I was really hoping a new MAF would fix it, it sure dun did made a lot of sense… but fuck it, it was only $2. :nanan?re Bought a proper Cobra MAF and housing that'll be on it's way tomorrow for pretty cheap anyhow.
Kingman: (2012-10-27 16:44:38)
Re: CHTS - problem or symptom?
Did the ECU input/output signal inspection. Power source and grounds for the ECU and to the sensors are good. Here's the problem areas.
TPS (-) 0V when throttle is open or closed, should be 9-10V
Fuel pump relay .75V, should be B+
Fuel temp sensor 3.36V, should be 0.5ishV
CHTS .78V plugged in and 4.93V unplugged, should be 1-5V depending on temperature
TPS (+) 11.45V, should be 9-10V
AFM .6V @ 5-700RPM and goes up to 3V when revving.
Real time diagnostics show the fuel pump is bad however it primes fine and builds perfect pressure… I think the PO rewired it off the ECU though.
FTS and CHTS are completely out of whack, especially the CHTS being plugged in VS. unplugged. What the fuck.
300zxturboftw: (2012-10-28 01:35:06)
Re: CHTS - problem or symptom?
I have the same issue so f*cking annoying!!!! If you figure out anything let me know please. I'll do the same. I've been trying to figure this out for 6 months now.
Kingman: (2012-10-28 02:10:08)
Re: CHTS - problem or symptom?
Will do man. I need to figure it out because it's my daily driver and it hardly drives anymore. When the green light clicks on the ECU it's REALLY bad.
Kingman: (2012-10-28 02:15:25)
Re: CHTS - problem or symptom?
Another tidbit… when plugging the CHTS in to the hot idling car after it's been in the freezer for 5 minutes it runs just about perfect for a bit, then as the sensor warms up it craps out. I've ohmed this sensor next to another brand new one and it's spot on.
Kingman: (2012-10-30 03:01:18)
Re: CHTS - problem or symptom?
Anyone got any ideas?
Careless: (2012-10-30 03:07:44)
i can see in your video that your distributor is not as straight pointing (parallel with the intake plenum body) as it should be.
my conclusion is that the distributor was rebuilt at some point with items from a pathfinder or maxima distributor.
i'm taking a guess because that's the orientation my 16E00 distributor was and the car ran similarly to how yours is. it just wasn't controlling timing properly when the engine was warmed up.
try changing the distributor and make sure the body of the unit says 21P00 or 21P01. if it's an old distributor, don't open it. try it with your cap and rotor first, and if it works out, remove the CAS and clean it up and put it back together. chances are it will work.
thats my take. i dunno. just goin by how the diz is pointed in yer vid.
Kingman: (2012-10-30 03:22:30)
Thanks for pointing that out, didn't really occur to me because it times at 20* just fine lol. This thing did run like a raped fuckin ape till a few months ago when it slowly started going downhill and last week hiccupped real hard then got to the pretty much non drivable point that it is now.
I just went and looked, says 22 100. May be a "P" but it's hard to tell.
Kingman: (2012-11-05 18:46:12)
Car started hitting the rev limiter at 5K. Back to the distributor…
chappo123: (2012-12-16 19:34:14)
Have you been able to sort this out or made any more progress? I have an 87 turbo with very similar problems - currently it runs ok from start, then runs rough once warm and after 5 mins stalls. If I disconnect the chts it will run smoother and continue to run. CHTS tests fine and has been replaced 3 times by PO. Most of the other sensors have been replaced as well. ECU is picking up MAF, although again it has been replaced. Connector isn't great but looks clean. Other thing is Idle control unit which I still need to check/replace.
Thinking it may be injectors ie they are only firing properly with rich fuel. Looking out with interest to so if you sort. cheers
Kingman: (2012-12-16 19:53:24)
Put a higher flow pump in it and it does run a lot better. Still just as rich at idle but doesn't break up as much in boost as far as I can tell. It's been rainy so lack of traction doesn't work for testing lol.
The ECU has stopped reading the CHTS as it now gives the code for it and yes, the wiring and sensor is good. It still starts right up on cold mornings. The air regulator for cold idling has also stopped working and is no longer getting a signal from the ECU. Even though that's stuck on the idle fluctuates a lot both in RPM and how groggy it sounds. There's a point though where it idles nice and high while being smooth and doesn't sound overloaded with fuel.
Basically I think the ECU is losing it's brains.
It's going to cost an arm and a leg to license it so I've been driving my pick up instead and kinda put the car on the back burner.
I'd try another ECU in your car man.
Kingman: (2012-12-24 22:33:07)
Lack of traction was a big problem for actually testing the car. Basically it still runs just as shitty when boost hits and backfires/stumbles on decel.
I tried another distributor, didn't help, so I swapped the original one back in. It's gotta be the ECU by now.
chappo123: (2012-12-24 22:59:48)
Think I'm gonna spend more time checking the wiring before spending any more money on parts - not that I can find anything in the UK anyway.
Keep finding wires that aren't attached to anything which is a bit worrying, as well as additions to the wiring yet to be figured out- might just be for the none standard radio, but not sure yet.
Just need some warmer and dry weather so I can work on it.
cheers
chappo123: (2013-01-25 19:07:40)
Latest update. Fuel modulator replaced, no change still stalls (on the positive side I got a job lot of spares/ecu's/turbo/ttops/lights/maf so some decent value). Got the UK/Euro FSM now which is also a big help. Figured out the cooling fans, one comes on when the aircon is switched on. The other should come on when the set temp is reached in the radiator.
Radiator appears to be a problem, thermostat appears to open ok, can feel hot water in top pipe to radiator. But radiator and bottom pipe remains cold, so clearly no circulation - query blocked radiator or could it possibly be the water pump not pumping (although was replaced around 5 years ago)?
Also located what a mystery wire is (not connected to anything). Think it is wired differently than US spec, hence I couldn't figure it out previously! It is the connector to the water temp sensor - the wire has broken off it leaving the wire unconnected. Could this cause the stall problem?
Still think something to do with the water not circulating through the radiator. Seems that after running smoothly for around 5 mins, it then runs rougher - appears to be when the thermostat opens, think at that point when water heats up and pressure builds, water is getting into the engine ignition[archived image: lb_icon1.png] area causing the water problem from exhaust, then finally causing the stall?
Any thoughts? Thanks
__________________
Z31 Turbo 1987 UK spec
chappo123: (2014-03-23 16:27:04)
Just for reference for anyone with my stall problem - finally sorted it out this week. Turned out to be a faulty injector. Inj #1 was ohm testing out at ~1.9 rather than ~3. The stall happened just after the engine warmed up and switched from simultaneous to group firing mode. What I think was happening was that in group mode, the faulty injector was impacting the performance of the other two in that group (shorting) causing the stall. Established this after finding the car continues to run when #1 injector was disconnected.
Managed to get another used set of injectors which were cleaned and ohm tested and fitted - now works. Annoying thing was also that the injectors were taken out and sent off for cleaning last year, but nothing to show they had been ohm tested and I wasn't aware either with my limited knowledge. Used a different company this time.
Anyway, now up and running, thought it worth feeding back after coming across lots of dead ends in my research!