I have a '91 z28 350 and it runs great when its cold at idle and driving. But when it heats up at about 160' it bogs, intake backfires, hesitates, and will die if you give it more than 1/4 throttle. You can drive it but no more than 20 mph if your easy on the gas. This has completely stumped me PLEASE HELP!!

i have replaced coil, plugs, wires, egr valve, intake temp sensor, o2, fuel pump, fuel filter, air filters, all vacume hoses, map sensor


cleaned injectors, throttle body

 

I had a similar problem with my '87 TPI 305 and it turned out to be the ignition module (located under the distributor cap). Are you getting any SES codes?

 

I had the ignition module tested and the pickup coil. they both turned out to be ok. they even ran it really hot to see if it would fail but it didnt

 

Ok i just replaced the ignition module and the throttle position sensor. Now it dosent backfire or hesitate as bad, but it still misses. Almost as if im only running on 6 or 7 cylinders.
Maybe my ecm is shot?

 

Not likely. You sure all cylinders are firing? Could be a clogged injector, bad spark plug/wire, corroded terminal on the cap.

 

i rechecked all the wires and distributer cap and rotor
then i replaced the spark plugs and checked compression
all cylinders are around 190 psi so i dont think its valves or rings
but its still missing bad
im now leaning towards bad injectors but im not sure

 

Today i replaced the pickup coil but still no luck

please help!

 

My theory is:

Temperature changes the littles coil's resistance inside injectors. This condition change the injector flow rate, getting a low gas flow, lean mixture and bad power. ECM can't know this problem.

I don't sure, but I think about this,


Denis V.

 

What an appropriate handle - moneyman380 - because all you're doing is throwing good money after bad in hopes of hitting upon the problem. IMO, it's time to bite the bullet and take the car somewhere to have the problem properly diagnosed. Having the car scoped and scanned will probably cost you far, far less than what you've already spent.

-B

 

Sorry this ain't going to help you a bit but...........

Whoa, I THOUGHT this was a 'DIY' kind of place.
The man is asking for advice and help and tips.

It's not 'throwing good money after bad' is it?
Isn't it just 'paying for experience'?

I know I have spent a LOT of money on experience.
Haven't spent a dime on paying someone else to work an my vehicles however.

Have you not heard the old saying:

Education is EXPENSIVE..... The lack of education is MORE expensive.

We all have got to learn somehow.

Once he figures out the reason for this problem, HIMSELF, he'll be set to solve a lot more problems of this type.
He'll learn a LOT in the process and next thing you know, he'll be on here OFFERING GOOD ADVICE to folks.

NONE of that will happen if it goes to a shop, right?

 

moneyman380,

Start by investing about 30-35 bux in a Fuel Pressure gauge.
This is a great diagnostic tool for a fuel injected engine of ANY type.

Get a fuel pressure reading by hooking up the FP (Fuel Pressure) guage to the schraeder valve on your fuel rail and taping the gauge to the windshield.

Drive the vehicle until the problem manifest itself and check the fuel pressure.
It' it's ok that elminates a whole BOX FULL of parts as being 'maybe's.

Next, has the MIL (Malfunction Indicator Lamp) or Check Engine light illuminated NOW or in the PAST?

If so there can be some GREAT information stored in your ECM that can help you find the cause of the this problem.

Use your Haynes or whatever manual you have to pull the codes from the ECM using your existing Check Engine lamp.

Post back here with your findings on the FP and the ECM codes.

 

It is. He just replaced a shopping cart full of parts he didn't need. (interestingly enough, I didn't see a CTS in there anywhere)

It can be construed as such, but it's money wasted on the exceedingly wrong kind of experience, IMO.

The thing is, it doesn't appear he can solve the problem himself. He's already into it for what is in all likelyhood a ton of money, and has nothing to show for it other than a light wallet, a bruised ego, and a car that still doesn't run right. People can make suggestions as to what may be wrong all day long, but the reality is that nobody here will be able to help him diagnose the problem unless he himself has a basic and working knowledge of the troubleshooting process.

At this point, I think it would be terribly irresponsible for anyone to suggest that he replace any more parts without someone first competently diagnosing the problem.

What will happen if he goes to a shop is that his car will be fixed. The lesson he will have learned is that throwing parts at a problem is no substitute for proper diagnostic procedure.

I think your suggestions to him of investing in a fuel pressure gauge, pulling codes, etc... are good ones. However, those needed to be done before the first dollar was spent on replacement parts. If it were me, and if this car were my driver, this is the point where I would cut my losses and just go get the thing properly diagnosed and/or repaired. THEN I would start stocking up on basic diagnostic tools such as a fuel pressure gauge, vom, compression tester, etc..., and spend the time between now and the next problem learning how to use them.

I mean absolutely no disrespect to the guy - the gods only know the messes I've gotten myself into in the past - I just think he got started on this the wrong way, and is in much deeper than he needs to be as a result.

-Bob

 

Before to arrive to this forum (may 2002), I spent a lot of money for "masters", "experimented" and "best" mechanics trying to solve problems in my vehicles.

Today, I know a lot, (I use my time, I know it) but to solve mechanics/electrical/computers issues in my cars cost me 1/4 - 1/8 than previous method.

Regards,

Denis V.

 

my 1986 305 TPI has the same problem... i replaced 3 ignition moduals, plugs, distributer...

IT"S STILL F_U_C_K_E_D UP!!!!!!!

 

Im no more than a shadetree mechanic with a few highschool level automotive classes under my belt but ive never payed for a mechanic to fix any of the three cars i have owned including my 91 z28. I have never wanted to just give up and take a car to a shop just because i didnt understand how something works and i dont intend to start now. I have rebuilt two engines, replaced transmissions, rebuilt rearends, starters and alternators. I did all the exhaust work on my camaro (headers- cat- flowmaster muffler) myself, installed a new fuel pump, learned how to sew just to be able to make my own door panels, built my own custom sub box and amp rack, installed a remote start car alarm, dynomated my intire interior and after i fix this problem i plan on repainting the car myself. id rather do everything myself so i get to enjoy the sense of accomplishment and futher my trade skills, instead of paying someone else who may or may not care as much as i do about craftsmanship.


i did all of the basic tests before i replaced anything including compression, wires, plug gap, fuel pressure, fuel volume, vacume, cylinder leak down, rotor and cap, and check for codes but there have never been any stored or displayed by the check engine light.

the only reason i just started replacing sensors is because i got frustraded and did not understand how tpi works. But now thanks to everyone who has posted and all the great info on this site i have a better understanding of how the tpi system works.

So last night i found the problem it was a faulty egr valve, i replaced the faulty stock one with a defective new one that was stuck in one position . problem fixed by a $60 part after $100s

thanks autozone!!