Hey guys.. Got a new car and a new issue. Car is a 91 z28, 5.7 l98. I bought the car and drive it 3 hours straight home. Never even had a hiccup, ran awesome the whole way. Changed the fluids and put her on the road.

First day on the road, 2 hours in she started idling a lil rough so i turned for home. She popped, spit and sputtered all the way home but made it. Pulled a map sensor code. Replaced map the next morning and it still idled rough.

Second day, same thing 1-2 hours in she started missing and popping again. Pulled over found distributor loose. Limped to a friends, let it cool and set the timing (way advanced) and tightened distributor. Same day on the 30min trip home it died again after going in a store and coming home. Lean o2 sensor code, replaced o2 sensor...

Third day, same all over again. Noticed fuel pump getting loud so i checked fuel pressure.. (35psi idling) so i let it run until the problem happened. Took 45mins of idling, started missing and dying. Fuel pressure was <10psi shaking up and down. Pat the gas and it dropped to zero like you cut the key off.

Replaced pump and checked pressure. 37psi, and rises to 42or so when revving...
Still hard to start, takes some turning over to get her going but the pump was quiet and i couldnt get it to mess up. So i took it out. 30mins tops and i was stranded again. Wouldnt fire. So i searched tgo while waiting on a ride to work and read about swapping the relays around so i did to no avail.



Came back a few hours later. Fired up and drove home. Checked injector ohms theyre all 16.5-17.2 cold. Planning on checking them hot..

I also tried a new ecm. Didnt work. Car has a afpr, and recent injectors, the map was new when i bought it. The ecm also looked recent. I think whoever owned this car chased this problem to.

Would a icm cause hard starts? The car also surges randomly while idling...

What do you guys think?? Open to all suggestions...

Edit:: just to be clear i didnt change the injectors or the afpr. They were on the car when i got it. They injectors are yellow and dont look like my brothers injectors (same identical car) his car always fires on the first turn. Mine has to turn and turn and turn then fires kinda weakish...

Thanks tgo!

 

You've sure replaced lots of good parts, with good parts!!!

Do you have a multimeter? If the circuit breaker in the house is tripped, then you can swap bulbs in the socket until you can see your breath in Hades, and I think the bulb ain't gonna' light up...

Good job testing fuel pressure tho'. Was that static FP (motor off), or dynamic (motor on) ?

I'm taking a stab, since you say revving pressure, that you didn't do static, or if you did, you didn't do leakdown time?

I'm guessing that you have leaking injectors, which will cause hard hot re-start, since GOOD atomization is MORE important for hot start. Leaking injectors don't matter to a cold motor.

Why?

Gasoline vaporizes better in a cold atmosphere (think Cold Air Induction). Think how water drips out of a garden hose, if the nozzle has low water pressure behind it (since in this application, the garden hose has 7 OTHER nozzles sharing the same water pressure (8 others, if it has a Cold Start Injector, which I think only has pulsewidth when CTS reads cold???).

Anyway, when motor's HOT, all injectors need to do their share, and hold closed when the other one[S] is / are [batch fire] opened. One guy lets go, and the others don't have good pressure, which is necessary to come out HARD, and spray FINE MIST, QUICKLY!!!

Your vac supply to FPR could also be allowing fuel in, from a ruptured FPR bladder. Same effects as leaking injectors - lower pressure, and fuel comin' in in a 'vacuum hose [injector] - sort of...

The FPR spring IS good. A bad spring, although it would allow dynamic linear pressure loss, would NOT necessarily make hot starts any harder. It could make the motor run a little hotter, depending on hammer style.

Maybe read the article that I posted (NOT my work - I just recognize good stuff). It will take a COUPLE of reads, to pick it all up (I just read a part that applies to my LT5 ... )

TEACHER (and LEARNER) OUT!!!

 

Ok thanks for the knowledge. I just finished that article.

I just came in from checking the injectors warm. While i didnt have time for it to run for a hour and start completly dying. Every injector tested lower than before. One of which dipped into the high 15s.

I get 40psi when i hit the key on dont start it and it takes about 2 minutes to leak down to 30psi.

Also the car takes a few turns to start cold or hot. But when it dies it wont start for a few hours. Always dies after riding highway for a while..

 

2 minutes to 30 PSI sounds good to MAYBE BORDERline - I don't know what spec time is for pressure holding, but do leakdown one more time just to see consistency. Then maybe someone can post if it's good or bad (problem here is the ones who SORT OF know, don't post, unless you make a mistake).

Warm injector resistance is good.

Does it have a loping idle when warm? (thinking of vac leaks here) ONLY if so, check here:
https://www.thirdgen.org/forums/post...45-post30.html

If not maybe go to MAP code diagnostic procedure. Sans other codes, that's the only concrete clue right now. You have FSM Factory Shop Manual? But first, are your spark plug wires properly routed, IN THE WIRE LOOMS?

Mis-routed wires COULD be the source of the MAP code, and the cold start problem. They'll emit EMI, same as a nuke, and solid state sensors ain't happy with that.

 

I havnt gotten the map code since i replaced it. Somebody told me the only reason it threw it is because the vacuum dropped when the car was barely running. It does have a loping/erratic idle after warm along with some surgjng.. i do not have a fsm. I ran the wires in the same place they were already ran but no they dont have wire loom on them. Theyre just snapped into the original holders..

I do not see any sparking/arcing at night with the hood open..

I can tell the plenums have been off before. While looking i found one bolt in the upper plenum is tight but not all the way flush with the runner. Going to fix that when i get home.

Also when i bought the car they had a spare runner (passenger side) in the trunk.. i do not know why.

Thanks again.

 

K a little more info for anyone who cares to help..

I tested the pressure again. When you hit the key it pops up to 40psi, as soon as the pump kicks off it drops fast now. Drops to 20psi within a matter of seconds.

Something else i found odd is theres an adapter on the tps.. has one female end and two male ends. The original wiring is plugged into the female and one of the males go into the tps and the other male end is just laying there. I tried it with and without the adapter and it made no difference. I have not replaced or tested the tps yet and will do so this evening..

 

The piece on the tps might be a snake oil Casper tps enhancer . Pinch the return line the rubber crossover the smaller hard line of the two. If the pressure doesn't drop the issue is with your regulator. If it does you have a faulty injector or injectors. You can cycle the key miltiple time and pull the plugs looking for wet plugs. I didnt read the above and am not sure if you pulled the vacuum hose to the fpr to see if there is any sing of fuel indicating a rip in the diaphragm.

 

Which lines are we talking about?? I just took it out for a fast spin. While filling it up, it began to rev itself to 1200rpm over and over..

Im suspecting the injectors ohms are getting lower and lower as they get hotter. Then eventually fail, leaving me stranded..

 

the cross over lines are the two rubber lines that jump from the frame rail to the hard lines bye the act/ps serpentine bracket.

 

Just a suggestion from a very similar problem I experienced years ago on a truck.

The truck ran great for 20-30 minutes and would then die and not restart. Let is sit 20 minutes and the truck would start right up and run another 10-20 minutes. I spent lot's time doing many of the same actions you have taken. Same problem continued. 2 GM techs looked and could not find the problem.

Started staring at the engine compartment one day and found a 3/4 inch section of wire insulation was MISSING from one of the wires going to the distributor. The wire was buried down near (not on) the intake in a high heat area. I cut the wire removing the bare section of wire and properly spliced (soldered) the wires back together replacing the section of wire the missing the insulation. I used shrink wrap to cover the repair to provide insulation and NEVER had a problem again!

Apparently the heat from the engine would cause the wire to get hot, the resistance in the wire to become to great and stop the flow current flow thereby stopping the power/signal to get to the distributor and the engine would stop running. Remember (Voltage = Current x Resistance). If the resistance gets to great due to heat the current will get low and reduce or eliminate the voltage in the wire.

Suggest you look at the wires in the ignition system of the car AND the injection system. Pay particular attention to areas were the wires are close to the intake manifold or other high heat areas.

After all the car is over 20 years old and there is a good chance the wire insulation might have become brittle.

You may have a wiring problem.

 

K i will try the hose trick. Thanks for the advice.

Ill also start checking sections of the wiring. I thought about it having a wiring issue.. time to start checking.

Thanks again both of you for replying and trying to assist.

 

Ok.. pinched the hose. Pressure spiked to 70-80ish fast... so that means my injectors are bad?? Not sure im getting it... could you explain this further??

Shes running but constant up and down. When you run it hard it kinda surges while the pedals down. Hard to explain but it pulls hard then easy, then harder, then easy really fast.. almost like lag. Checked as much wiring as i could. Didnt see any obvious problems...

I did notice all my connectors have the tabs broken off them.. but none make a difference when wiggled.

Id really like to fix this car. I paid good money for this car and got screwed somehow. It made it the 3 hour trip home and hasnt made it a full trip without breaking down.

Edit-- im also checking on getting the cable to data log but im wondering will it really help diagnose this problem or will it just be more money wasted??

 

You have a vacuum leak. Do this to find it.
https://www.thirdgen.org/forums/post...45-post30.html

 

Ok i have noticed my intake is seeping antifreeze so its pretty obvious i have an intake leak.. im still going to do the test above. Im willing to do whatever it takes to fix this car.

Just wondering though. The vacuum leak is contributing to the idle issue but why is my car dying after riding????

 

One thing at a time...

 

I am having the same issues with mine, any luck so far?

 

I wouldnt give up on your car. These are annoying problems but relatively low cost and simple to fix then troubleshoot. Start simple and one thing at a time.

With any old car there are bound to simple things broken that make a big difference. I sually look at things this way. Air Fuel Spark.

Go through all your vacuum hoses to the throttle body egr, run the car and check for leaks like you have at the gasket seams. Many ways to check. but little propane in a can or start fluid (CAREFUL) but just little liquid around gasket points and connections and see if car idle increases or if you notice liquid getting sucked in.

I also while doing that pull the TPS, Distributor and injector plugs clean them up make sure not corroded or worn. Usually you will have one bust off in your hand.

Do all that and check your vacuum at idle.
Vacuum will will tell you a lot for what the engine does.
Ideally it should be sitting rock steady at 17-21" other issues will be easy to spot and will point to your problem easier (I hope)

http://www.freeasestudyguides.com/en...cuum-test.html

 

No progress so far.. been super busy with work. Havnt given up on her yet. Tomorrow im going to get a vacuum gauge, some starter fluid and a fel pro intake gasket set. I know my intake is already leaking coolant down the front of the engine so thats going to have to be done anyways. Its gotten worse so i assume the 3 hour ride on the highway finished it off and caused my new problems...

Just a recap, surging idle, rich smelling (when i bought it the exhaust smelled like a new car and idled like one to) but i havnt had it die on me but i also really havnt driven it...

I hear a lot of hissing from the engine to but heard it was normal for tpi engines..

Thanks guys

 

A hissing noise? From all the symptoms you have described sounds like somebody changing out the injectors one time did a crappy job resealing the intake and runners. But that's only half the problem, even with a intake leak after driving for a while it will start the car and have the surging problem, but the car would still start, it would just run like crap. I think the fuel injectors maybe a factory in this too.

 

I agree. Theres a bolt on the top plenum thats not even all the way in. Going to go back through it and do it all right.

Also the thing about it dying was right before it would die, the fuel pressure would drop and the pump would get loud. The last time it died on me (after changing the pump) it was like it ran out of gas although reading half a tank. I left it for a while and it wouldnt start. I added a half a gallon and it fired up. Its a very confusing problem to have. Im so paranoid to drive it out now its hard to want to test...

 

[quote=LowBird87;5623817]I agree. Theres a bolt on the top plenum thats not even all the way in. Going to go back through it and do it all right.

Also the thing about it dying was right before it would die, the fuel pressure would drop and the pump would get loud. The last time it died on me (after changing the pump) it was like it ran out of gas although reading half a tank. I left it for a while and it wouldnt start. I added a half a gallon and it fired up. Its a very confusing problem to have. Im so paranoid to drive it out now its hard to want to test...[/quoteen]

Forget driving it out to test.

Pull the plenum and runners, set them with new gaskets, with a thin grease film, STERILE, then KNOW there's no vac leaks.

Then...

BASIC stuff; air, fuel, fire.
Air - air filter OK? (and no leaks, of course)
Fuel - static fuel pressure, no leakdown.
Fire - static timing, wires routed PROPERLY, to not emit EMI (like you did before), and plugs.

Then code check.......

Master wrench OUT!

 

Alright guys... did the whole intake with new gaskets.

Fired her up, timed it. Running pretty good, although i think ill change the plugs.

Drove her for 30minutes and it feels better so i got my fingers crossed. I also think the vacuum line was off the egr. I noticed it while removing the runners. Dont know for sure if i pulled it off accidently or not. Best off all my coolant leak is fixed.

Ill change plugs, drive some more and update further.

 

Sweet great news. I suspect I will be in the same boat with my car. Vac leaks on original gaskets it bogs down bad off idle no power. Could be rich

 

Ok guys. Today after cruising around for about 10 minutes or so i stopped at a stop sign and threw it in neutral to see how she was idling and it popped up to 1200rpms. Full operating temperature. All the new parts listed above. No check engine light so no codes. Timed right, no vacuum leaks, injectors ohmed out, fuel pressure good.

Im still to nervous to take it very far. I dont have much faith in the intake gaskets fixing the problem of dying after a hour ride. Although i havnt been able to reproduce after the gasket change. Im thinking of taking the ICM and having it checked. Its a newer looking gm icm. Just wondering if it would check out cold and fail hot..

 

Highest it should been idling at warm operating temp is 700 neutral or park. Is still surging or is it just idling high?

 

Check, the coil, pickup coil and ign module all while hot.

 

It had a surgjng problem before gasket change. It would throw a few random revs in here and there idling. Then it would hold a high idle when it wanted to, then drop low. A lot of times while stopped in gear the car would want to pull off on its own. While i couldn't get it to surge while idling in my driveway right after a ten minute ride it was idling high. Im pretty sure its still the surge issue..

Do you mean check the coil, pickup and icm with a multi meter?
Thanks for all the input guys...

*edit* confirmed surging issue. Fired her up, runs awesome, smells clean, idles nice.. once the temp gauge gets about a third of the way up she smells like RAW gas bigtime! Has a random surge while idling in the driveway. The richer it smells, the worse it idles i noticed...

 

Another update...

Pulled the icm, had it checked. Passed 4 out of 5 test. Failed the''bypass test", replaced it and took it for a 50mile ride. All seemed well, no cel, no problems. Got up this am to warm it up for work, and it started surging after 10mins idling. Seemed like a random dead miss would hit then car would stumble then rev and throw code 33 again... whats going on???

New icm, fuel pump, wires, map sensor, tried a different ecm, injector's ohm out good. Replaced all intake gaskets.

Anybody have any new ideas? Im thinking bout checking the ignition coil...

 

Code 33 is normal for an engine that is struggling to run.

Check the terminals and connector for the CTS (coolant temperature sensor). If they are even slightly dirty or corroded looking replace both. As the connector resistance increases the ECM sees a lower then true coolant temperature (dash uses a different sender).

So the ECM adds more fuel then it should, and most of the time won't go into closed loop.

This is where a scan tool is helpful as you can see what the ECM is seeing for sensor values.

RBob.

 

Did you ohm check the pickup coil?
What ICM did you purchase? GM or ?

 

Alright guys. Bought a new bike, been tryin to enjoy the rest of the season.

Anyways, fired the z up today after sitting for a week. It just barely started and roughed its way up to fast idle which is a first. Usually while slow to fire, when it does fire its gets running pretty quick.

I put a cheap icm in it from autozone. Just to be sure i returned it and tried another. Last time it would surge randomly, well today after sitting for a week it had a constant surge. I let it run for 20mins or so, surging the whole time. I tapped on sensors, coil, ect to see if that made any difference but no luck. I unplugged random injectors to see if a certain injector being unplugged would help but nope. I did find a overlooked vacuum leak from the throttle body to the passenger valve cover.

A local mechanic suggested trying a new coil but i dont know. Its very depressing not being able to drive my z somewhere. Any input is appreciated.

 

With out one of these,

you won't figure it out and we are aren't helping, just guessing.

 

I had a similar problem with my 87' Z.. Drove OK for first 10 mins after start up, as soon as it warmed up it started idling rough and stalling...had to let it sit for 30 min to an hour before it would start up again...changed the Coil and it hasn't died since.