k.bit

Hi Everyone..I have a problem with my 1988 C4, the more I try to hit on the gas the less throttle i get and some smoke starts going out from the exhaust...they told me change the TPS, I did but the same problem is still there..today they told me i should buy the manifold pressure sensor and the fuel temperature sensor...do you think this will help? or I will still have to change the EGR valve? Thanks!

joe paco

black smoke from exhaust? did you mean coolant temp sensor? the CTS can be faulty causing over rich, pretty common. did you check for defect codes?
you have a MAF, not the MAP, but same animal. you can try unplugging it and the ecm will use a default setting. if it runs ok, that is a clue.

Stu 91 drop top

I don't think the EGR is the issue. You can plug the vacuum to it so it does not open. Is this only under load or just sitting and trying to rev?

96GS#007

No, but the "throw parts at it" approach will certainly empty your wallet quickly.

Who is "they" that's telling you all of this?

Do some trouble-shooting.

Is the fuel pressure regulator ok?
What's the fuel pressure?
Does the fuel pressure hold?
Ohm check the injectors
Is the cold-start injector ok?
Are there any codes? If so, what are they?
Did you check the EGR valve? If not, why do you want to replace it?
What's the timing set at? Did you check it properly?

or....just keep throwing parts at it. You might get lucky or you might have to spend a few thousand dollars.

k.bit

The problem is that I looked everywhere in Dubai for someone who can check the system, they all can check cars that are not older than 1991 :S...the software they have doesnt support 88 C4s.
Howcome its MAF and not MAP? I bought it from rockauto online and they mentioned it is MAP, please dont tell me i bought the wrong item this means ill have to wait for another week..
Ill try unplugging the MAF

k.bit

thats my problem; I dont know how the concept of technology is understood in this part of the world! I couldnt find a computer that can test the car! thats why i am guessing all the time

joe paco

I spoke too quickly. I THINK 88 was maf, but not sure. mine is 91, map. regardless, the book says to unplug it to see the reaction -to get a clue.
I assume black, rich smoke, but you didn't say. that can point to coolant temp sensor, if you have a code 15 or 14. also injectors, fuel press regulator.
I am guessing that you are not familiar with pulling codes yourself, thru aldl?

joe paco

http://corvettephotographs.com/c4vettes/codes.htm

add: compliments Cliff Harris!

96GS#007

Got it.

Trouble-shoot the items I mentioned above.

- The fuel pressure regulator is under the plenum towards the rear. Pull the vacuum line off. If there is fuel in it, the regulator is bad.
- Fuel pressure should be 39-43psi and hold with the key off, slowly bleeding down ~10psi over the course of 20-30 minutes
- Injectors should ohm test 15-16 ohms hot & cold. If an injector is over or under, it's bad.
- Remove the cold start injector and check for signs of leakage

The EGR isn't the issue. You'll get rough running, but not the other symptoms you describe. Nonetheless, you can remove it and verify it fully closes.

- How to check L98 base timing is well documented. A quick search will yield multiple threads. The cliff notes: Disconnect the ESC wire. Start the engine. Check timing...should be 6* BTDC, although it'll run fine anywhere between 4* BTDC and 10* BTDC.

For the record...your '88 is a MAF car. It also has a MAP sensor. The MAP sensor is used to keep the car running if the MAF fails. '90 L98 cars switched to Speed Density, using only the MAP (no MAF on the car). '91-'93 are also MAP cars (no MAF). '94-'96 cars switched back to MAF with MAP as a back-up.

k.bit

Sorry for replying late. thank you so much, this is very informative..i will try all those tomorrow or day after...when u mentioned the coolant temperature sensor u reminded me of something, i have the "low coolant" alert always on! could the reason be that the sensor is not working?