Looking for second opinion
Thread Starter
2nd Gear
Joined: Jul 2006
Posts: 2
Likes: 0
From: Lincoln Park Michigan
Looking for second opinion
I have a 1990 C4 L-98 that began with an O2 Oxygen sensor error and a slight miss at idle. The car will start, idle smooth and run great cold, but within 5 to 10 minutes at warm up begins idling with a miss and slight clatter that worsens. The computer was replaced with my original PROM chip put back in. Also the ignition module was replaced and made no difference. When the car is warm and running rough the spark in the first four firing order cylinders is weak and a voltage check on these four fuel injectors is also low leading us (me & my mechanic) to believe I have four bad fuel injectors possibly caused by the bad computer that was replaced. I’m looking for a second opinion before I spend the money on new injectors. - Thx C4Rob
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
I would blame the injectors yet. There are a few test to do on the injectors to rule them out. You will need to use a fuel pressure guage attached to the fuel rail and a ohm meter. Turn the ignition to on and see what the pressure is and how fast it drops. Use the ohm meter on the injector connectors (after removing the pigtails) and they should read about 16 ohm each (cold and hot). Next pull the spark plugs and look for signs of gas (wet plug).
Being that you know there is weak spark, the distrubitor components need to be checked. Do you know the IM is good even if it is new? Have you test the pick up coil, spark plug wires, checked cap, and made sure all have good connections. The distrubitor sends refrence pulses to the ECM, then the pulses are sent to the injectors. The 90 is still batch fire so each side fires at one time. The ECM could also be at fault but I would try the other things first.
Oh, I hope you/your mechanic is using a 90 FSM for refrence.
Being that you know there is weak spark, the distrubitor components need to be checked. Do you know the IM is good even if it is new? Have you test the pick up coil, spark plug wires, checked cap, and made sure all have good connections. The distrubitor sends refrence pulses to the ECM, then the pulses are sent to the injectors. The 90 is still batch fire so each side fires at one time. The ECM could also be at fault but I would try the other things first.
Oh, I hope you/your mechanic is using a 90 FSM for refrence.
Team Owner
Joined: May 2006
Posts: 21,473
Likes: 356
From: Palmdale, Ca----- 2009 Cyber Gray 4LT A6 F55 452 RWHP 422 RWTQ- RIP 1998 C5 734 RWHP & 585 RWTQ-----
Follow RRVette's advice on checking the OHM's on your injecter's. I hope you trust your mechanic, just be careful sometimes they will really try to soke a Vette owner. A lot of your questions will be answered here and you'll become a quick study on your own Vette in no time! Welcome!
Thanks,Matt
Thanks,Matt
Cruising
Joined: Jul 2005
Posts: 10
Likes: 0
From: Ewing KY
Have you replaced th O2 sensor? When you first start the car it is probably running with the fuel in open loop and is putting in a default number for O2. When it warms up it it switches to closed fuel loop and looks at the O2 sensor to determine the injector firing rates.
Thread Starter
2nd Gear
Joined: Jul 2006
Posts: 2
Likes: 0
From: Lincoln Park Michigan
Originally Posted by RRT vette
Forgot to mention, welcome to the forum. This is a great place to discuss corvettes and alot of information to be read. See you around. 
