1990 NA. Bucking, sputtering, surging, barely idling, no power, jerking.. Its a mess..

[everpresentnoob]

Ok, where to begin. Fixed the AC last weekend and finally put a belt on it. AC worked great. Driving to work on Friday car was running great. suddenly out of the blue it started backfiring, surging, popping and generally loosing power and running like crap. managed to limp the last few miles to work. When it was acting up, trying to get out of the fast lane on the interstate in 5th gear, flooring it, but the car was still slowing down from 70mph. Yea, I know, I shouldn't have been trying to floor a motor running like that, but it was that, or get nailed by other cars. Limped into the parking garage at work and it would not idle. Stop lights and stop signs the last two miles were an exercise in playing with the throttle and the hand brake. FYI, the hand break alone will not really stop you from 40 mph....

during the work day I managed to go out and do basic troubleshooting... Checked ECU for codes, there were none. Pulled a few connectors apart, but they didn't look to bad (MAF, PTU, TPS, coolant, coils adn injectors). basically couldn't find anything glaringly wrong with it. That afternoon when I fired it up it idled perfectly. took a chance and started heading home with it. 83 miles. first 25 are in generally stop and go traffic. Car ran like a dream. well mostly. Last quarter mile it would occasionally hesitate as if the fuel or something were cut suddenly and then it would pick back up a second later. It did that a few times.

went out to it this morning and fired it up. Chugging pretty badly and running rough. just like when I had a dead injector. Sure enough, middle one on the passenger side was dead. Replaced it with a spare used one I bought from a guy here. Car ran pretty good. took it on the road and it still had the occasional hiccup.
I replaced the fuel filter as I was thinking it may be a fuel issue. continued to clean some corrosion off a few of the connections. Pulled the AC belt back off in case the AC compressor was seizing momentarily and dragging down the motors RPM. Took it on the road and it was running fine. drove for about 30 miles. all was good until suddenly it started acting up again. Almost didn't make it home.

Got it back to the house and started searching for things that could cause it. Came on a post about the TPS. Ok, went out and used my meter to check mine. On the TPS plug when you check ohms on the two outer pins the resistance was 9000. with in spec. inner and the outer black wire ohms should be 1000... Mine was 345. Ok, that dosent seem right. Read a number of threads here and on TT.net about it and determined that my TPS was not within spec, so I replaced it. Put the new one in and all the tests worked out. got the voltage from the middle pin to ground to be .45.

Car now holds and idle for about a min, then does its popping, breaking up thing and drops to almost stalling, then surges to 1500 and steadys out at 850. it is still undriveable though.

After all this I thought to check for codes again. 34, Det sensor.... ok, cleared it from the ECU and drove it around about 5 miles. not smooth at all. Still doing the same thing, although not quite as bad, but definitely not trying to actually depend on it to get me anywhere like it is. Got it home and checked codes again to see if 34 came back, but nope, no codes.

I am about at wits end here. what else should I check? I can get a new Det sensor and harness from Concept z for 75 bucks, but if that aint the issue I dont want to do that. Car is stock, mostly, just a cheap catback and a k&n filter up front.

[rgregoryb]

Being a NA I wouldn't worry about the detonation sensor.I ordered the plug in resistor from them over a year ago and my NA runs fine with it. Man, you are going to have to go through your entire systems one by one. Could be many things.

[z.Leinbach]

Check the ptu and pull the cas apart

[nexus08]

When my coolant temp sensor was acting up the car ran like what you are describing. Being a very cheap part, that might be a first place to look.

[everpresentnoob]

Pulled the PTU in anticipation of getting a replacement from a member here (Thanks Dcaff). Pulled the CAS and opened/cleaned it. Wheel wasnt bad at all, but hey what the heck. Put the cas back in and the car wouldnt even start. It would spin over but wouldnt even try to fire. after about 5 mins of head scratching I went inside to log on here and google a few things. sat down by my computer, moved the PTU so i could use the mouse... Um.. Yea... PTU is in the house... Decided to NOT work on my car anymore this weekend...

Ill revisit it later today when the new PTU is here, and I actually put it IN THE FREAKING CAR!!

[javadave]

Pulled the PTU in anticipation of getting a replacement from a member here (Thanks Dcaff). Pulled the CAS and opened/cleaned it. Wheel wasnt bad at all, but hey what the heck. Put the cas back in and the car wouldnt even start. It would spin over but wouldnt even try to fire. after about 5 mins of head scratching I went inside to log on here and google a few things. sat down by my computer, moved the PTU so i could use the mouse... Um.. Yea... PTU is in the house... Decided to NOT work on my car anymore this weekend...

Ill revisit it later today when the new PTU is here, and I actually put it IN THE FREAKING CAR!!

Literally lol'd, reminded me of a time me and a buddy did a tune-upon on the 87 IROC I had before trading it in on my first Z (TT). Intended to do the plugs, rotor, wires, dist cap and fuel filter. Got it back together, tried to start it and it wouldn't. We scratched our heads trying to figure out what it was for 20 minutes before calling my dad. He came over, looked at the dist cap and said, "I see your problem !", pointing to the rotor that was sitting on top of the dist cap. Mind you, we were both pretty stoned by the time we were putting it all back together. Lesson learned there !

[everpresentnoob]

well put a new temp sensor in it, replaced the PTU with a known good one, pulled the CAS apart and wiped it down. Cas looked just fine inside. No dust or anything.

Took it out this morning. runs worse. as I limped it home I could push the gas pedal and nothing. it was as if the car was off and I was pushing the pedal. Gonna go disconnect the fuel pump, pull the cas and spin it. kinda hoping that my injectors dont click... I just wanna know whats wrong with this thing!

[everpresentnoob]

Ok, puled one of the coils and unbolted the CAS from the block. putting a spare plug in the coil and grounding against the plemun gave a nice spark on all coils. and I hear my injectors clicking. there is some relay or such behind the plenum that clicks as well. reading other threads about CAS testing this way I have seen a number of people asking about the relay behind the plenum clicking, but none of the people answering them mentions it, what it is or if it is normal.

This weekend I am going to do a compression test. Yea, I know I should have done this before. Car runs decently when cold, but once it is good and warm, like after 20+ mins driving that is when all hell breaks loose.

Also tonight I noticed an odd clattering noise under the front of the plenum that is RPM dependent. Lifter? regardles Im sure its not good. If this engine is toast I can not and will not be rebuilding it. Its just not worth the money that would take.

Any ideas?

[everpresentnoob]

Well just checked Compression. everything is 170-180. This was done with a cold engine. Would a hot engine be higher or lower? I would think higher as heat would make things expand causing a better ring to cylinder seal, right?

[JJT211]

Why dont you just run it til its warm and compression test it then?

Also, when you reinstalled your CAS, did you set timing afterwards?

[everpresentnoob]

when I puled the CAS I put scribe lines on the mounting plate so that I could reinstall it in the same place. Ill double check the timing later.

[JJT211]

Have you checked fuel pressure?

Im having similar symptoms on my 90 TT and just found out my fuel pump is likely bad. Its only pushing out 10 psi and ohming out around 2-100 ohms when it's supposed to 0.5

I was pulling my hair out checking over all the sensors that I kinda glossed over fuel until today.

[everpresentnoob]

That was one of the first things I checked. It felt like I was hitting fuel cut. My pressure was good. Then I started looking at the Fuel Pump Controller, thinkng it was going bad. Bypassed it but no change. Thats when I started playing with all sorts of sensors....

[JJT211]

Hmmm....Damn dude this is tough one......I know the manual says to do it after the fuel filter, but maybe you can check it after fuel damper right before it goes to the injectors.

Also if you still have your PRVR, you can bypass that as well. If that's all good and you're not getting any codes for misfires, fuel is good.

[everpresentnoob]

Yea, thats one of the fun things about this entire debacle... I am getting no codes for ANYTHING! Makes for an interesting troubleshooting experience. Shoot from the hip and go from there.

I think I may have found a problem yesterday, totally green connectors on the main harness to the ptu. I had cleaned the contacts pretty well, but back inside the connector where the factory had crimped the terminals to the wire was nasty. I ended up cutting the connectors out and soldering in my sub harness so that now my main wiring harness has the new style PTU plugs on it. Drove for about 30 mins yesterday and no issues. Gonna be tomorrow night before I can drive it any more to see if my issue has cleared up. But my fingers are crossed.