Greeting from norway guys.
my first corvette. 1991 c4 convertible automatic.

i have a issues maybe someone can help me with.

when the car is cold, it runs like a crazy. Agile, powerful and like a corvette.

after driving it for about 20-25mins. When it gets warm.. it bogs down… less power. Very noticeable!
pull the codes, it gives nothing.

when its cold, put foot on brake, 60-70% throttle, its burnsout straight away,
when warm.. foot on brake. 100% throttle, not enough power to even spin the tires..

getting frustrating.

the car have done 125.000km. And seems in good condition.

 

coolant temp sensor maybe? Some say the ignition control module can be flaky and behave poorly when hot.

 

likely cts but can u used aldl cable to scan while running?

 

Allready checked the coolant sensor, its not that one. Will check the injectors tomorrow


but i got a H42 fault yesterday. I dont know if that can be something.. i reset it, it it dont come back, but the issues is still there.
goes like he** when cold… feels like it have 100 horsepower when its warm

 

 

https://www.corvetteforum.com/forums...nk-inside.html

 

Thanks guys. The h42 only came once, the check engine light came on. Drove it home. Check the codes. Cleares the codes. Drove it for 1 hour. Dident came back… but the car still behaves badly

 

if you dont mind me asking which coolant sensor did you check and were the temperatures correct at ambient in closed loop?

do you scan?

what is fuel pressure doing while you are experiencing the issue?

what are fuel injectors resistances cold vs hot when it is experiencing the issue?

what type of injectors are in the car snd do u know when they were installed?

let us know and we can help.

 

I used this one to check CTS

» On the C68 A/C controller, press and hold the up and down fan buttons simultaniously for about four seconds with engine running. The display will show 00. Use the up fan button to scroll to 16, then press the auto-fan button. The display shows the engine temp (in degrees C) being read by the coolant temp sensor. You actually have two sensors on the '90 L98: one for the gauge (right side of block) and one which the ECM (and the C68 module) uses (front of intake below the TB). If the display temp on the C68 and the gauge temp (which is only approximate) are close, the sensor the engine control module uses is good and can be ruled out as the cause of your problem.»»

they both show the same.
i did not scan, dont have a scanner for this car.

i will check the injectors tomorrow.
have to buy a multimeter as i cant find mine😂😂


i dont know what injectors are in the car. I bought the car 2 months ago.

i also got a tip, that it could be vacuum in the gas tank.. as i allways hear a loud «swuuuch» sound when open the tank to fill.
got a tip to drill a hole in the filler cap and see if it helps…. Dont know if this is a good advice or not….

 

I used this guide to check cts:—



« On the C68 A/C controller, press and hold the up and down fan buttons simultaniously for about four seconds with engine running. The display will show 00. Use the up fan button to scroll to 16, then press the auto-fan button. The display shows the engine temp (in degrees C) being read by the coolant temp sensor. You actually have two sensors on the '90 L98: one for the gauge (right side of block) and one which the ECM (and the C68 module) uses (front of intake below the TB). If the display temp on the C68 and the gauge temp (which is only approximate) are close, the sensor the engine control module uses is good and can be ruled out as the cause of your problem.»



And they both show the same.

I dont have a scanner, just did the standard code reading by connecting two pins in obd1



I will check the injectors tomorrow as i cant find my multimeter, have to get a new one tomorrow.



I also got a tip by drilling a hole in the gas tank filler cap, as he mean it can be vacuum in the tank doing this.. i allways get a loud swoooosh sound when open the filler cap to tank gas…



I dont know what injectors are in the car. I just got the car 2 months ago. And the previos owner was a young guy who did not know much either….

 

ok thats good for cts then mr norsevette

do obtain a fuel pressure gauge and tape to windshield and drive around until problem occurs. what are your fuel pressures doing in all conditions. 👍


long as u r committed to one step at a time to diagnosis we can easily get you running perfectly. these tpi are very easy.

 

I love the people on this forum! So helpful.
i will try to get hold of a fuel pressure gauge,

will also ohm the injectors tomorrow, and come back with the result

 

be sure to ohm cold, and hot when issue occuring. you might want a set of gloves and practice properly removing the injector harness plugs a few times when cold.

 

Some things to be looked and thoughts.

It's almost like the timing is being retarded which would reduce power a great deal.
Something with timing or distributor.
Knock sensor
MAP sensor - behaves different when hot.
Air temperature sensor (probably not).

 

Allright guys! I manage to ohm all injectors today. Hot and cold.

cold: all 4 on the left side was 13.8. 4 on right side was 12.7-12.9.

warm: all 8 on 13.6-13.8.

does this look allright?


at least got to put new wheels on the car today
275/30/19 all round. With 5x120 rims offset 45. Fits like a glove. Rides beautifully

 

seems ok.

now purchase or rent fuel orrssure tester and stick to windshield and report pressures:

situation / psi. / bleedown
key on after prime/
engine idling /
engine off /

during normsl driving conditions
duri g the issue you are experiencing
when you go wide open throttle while driving