I've gota 91 z28 w/the 350, tpi, auto, ignition coil off the dist. This started 2 weeks ago, car was running great and i parked it by the house. 1 hr later it wouldn't start just cranks, had a spark but looked weak so i replaced the ignition coil and it started and ran ok. Since then its gotten worse like the new coil was bad, so i tried another new coil same thing. It runs but the engine isn't hitting right, normally it hauls 4.10 diff etc.. So i tore it down in the garage and replaced the plugs, spark plug wires, dist cap & rotor, checked the pickup coil and its ok. Took the dist.control module off and up to autozone and it tests good. Not sure if it would still test good after it gets hot so maybe its seperating a connection after running for a few minutes? Which is when the problem occurs when the car is in drive. Then i tested the ignition coil w/the ohm meter and it reads good. I checked the ohms on the fuel injectors and their between 11-14 ohms so thats good. Got a noid light but didn't try it since i can hear the injectors ticking while its running. Replaced the fuel filter and the fuel pump comes on for a couple seconds after the key is on. I don't have a fp guage unfortunately to check the fuel pressure. Sorry this is soo long but this is driving me nuts, i miss my 245 stock hp! Not worried about high hp right now lol just stock would be great! I'm open for suggestions plz!

Dan91Z28.

 

Oh yeah i also adjusted the tps sensor, its at .55 volts so that should be good. I hadn't messed w/it before but figured what the heck lol. Does the distributor have any plastic parts inside that could wear out? Car has 130k on it. The big round metal piece in the middle of dist. has a nice rust color but not cracked. Don't know what its called but the metal casing that goes around that is loose and i can rotate it some by hand, not sure if that is normal or not since i don't have another dist. to compare with. Also previous owner said the dist. was re-advanced before i bought the car, i didn't believe him since the dist advance is controlled by the ecm on this car i think?

Dan91Z28.

 

Also the timing is set at 8 degrees before, stock is 6 but i'm running 93 octance and so far its been doing great before this stuff.

Dan91Z28.

 

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anybody?

 

I didn't see anything about fuel pressure... thats another thing you should check... what you would be looking for is an inconsistancy or abnormally low pressure when the problem occurs... as far as ignition the pick-up coil and ignition mudule can have problems that are affected by different temps and moisture... so I would not rule them out even if autozone said they were ok... just food for thought...

zroc

 

Yeah i don't have a fp guage i can use unfortunately. If i have to take it to the shop i'll let them find that problem lol. I'm trying to fix this myself.

You do have a point about the dist control module etc.. not being under a load w/the autozone test. Its 70 bucks for a new module from the dealer so i'm trying to eliminate the other possibility's before i go that route. I could get one from autozone since their only 35 bucks but i heard their not really a quality part like from the dealer.

Can anybody else think of anything we have missed? I'm gona be hacked if it turns out to be something stupid i missed lol.

Dan91z28.

 

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Go get yourself a fuel pressure guage. They cost ~$30 at any autoparts store, any shop is going to charge you a minimum of 1 hour labor at a rate at least $40/hr. If the fuel pump doesn't hold pressure you've got a problem.

The TPS on 90-92 TPI cars isn't adjustable and doesn't need to be since its self zero'ing.

How about describing what its doing? is it just not starting sometimes or what? You didn't really clarify that.

 

Unfortunately i haven't found a fuel pressure guage at any of my local autoparts stores. I'll order one from summit i guess.
Basically what the car is doing is it still starts and runs and drives. Just not like usual, starts fine no prob but then when i take off hot/cold its the same, it just runs rough. Have to floor it to get a decent take off, engine feels shakey and like i lost 100 hp. Just noticed this today after the rpms are at 3500 on the highway and i nail it the tach floats around some and then when i let off it, it settles back down! This makes me think something in the dist is going out i dunno? From driving it appears that when i romp on it the problem is not as apparent, but at small throttle openings its weak and doesn't acceletate smoothly like it should. This is when the engine feels the worst, i'm used to a smooth powerband and great take off/passing power etc.. I'm spoiled i know but thats why i paid a chunk for my baby and take care of it. Heres a quick rundown on what i've changed or tested.

dist.cap
ign.rotor
spark plugs
spark plug wires
dist.control module
pickup coil
fuel filter
injectors restistance between 11-14 ohms & they tick when
running

Its not fouling any plugs either. I thought maybe bad gas a put a can of fuel line dryer in and fuel injector cleaner in. Cleaned the plenum w/carb cleaner & got out the deposits 250 miles ago also.
I hope this clarifiys things some more cuz i really appreciate you guys help!

Dan91z28.

 

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The symptoms you describe make it sound like the engine is choking; could this be caused by a clogged catalytic converter? I don’t know if there is a way to test for that, other than replacement.

 

Yeah it could be a bad cat but my car has duals and would they both clog in a couple days time? I doubt it but thanks for the suggestion!

Dan91z28.

 

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My car had similar problems, under part throttle it was so so but you could tell power was down, floor it an it was pathetic and Im use to enough power to hit mid 13s on tire. Even though you have dual cats, each cat handles the exhaust from one side of the engine, so if one was plugged it wouldnt route thru the other cat. Mine turned out to be that a piece broke off inside the cat and turned sideways and clogged up the cat while the other cat flowed like normal. I had a pair of Catco cats welded into place and the car was like new again and all this happened with 94k miles on the clock. Im not saying this is your problem but a possibility...

 

Yeah i better check out the cats, thanks for the info.

Dan91z28.