C4 Intermitent Problem When Warm (please Help!!!)
Thread Starter
Instructor
Joined: Feb 2008
Posts: 170
Likes: 0
From: hopatcong NJ
C4 Intermitent Problem When Warm (please Help!!!)
Hey guys, im sure some of you will read this again as this is the third time im posting, all the feedback was great but unfortunity im still having an issue and im very frustrated, so here is the deal, i have a 1994 lt1 and this problem only happens when the car is warm, never ever does it cold, car starts up fine, then rpm's drop and is either starving or lacking fuel, after about 20 secs it stop and car drives perfect, never does it at a light only at intial start when warm..and the weird part is sometimes its fine...im pretty sure this is a fuel issue not a tune-up/elec issue, some have said fuel presure reg, any way it could be this????i need some feedback from you experts, i have replaced coolant sensor that feeds computer, i have cleaned TB, i have done top engine clean, fuel injector clean in fuel, dont know what the next thing to check, please help this is driving me nuts!!!!
Safety Car
Joined: Jan 2006
Posts: 3,566
Likes: 4
From: Mt Laurel NJ
St. Jude Donor '06-'07
Hey guys, im sure some of you will read this again as this is the third time im posting, all the feedback was great but unfortunity im still having an issue and im very frustrated, so here is the deal, i have a 1994 lt1 and this problem only happens when the car is warm, never ever does it cold, car starts up fine, then rpm's drop and is either starving or lacking fuel, after about 20 secs it stop and car drives perfect, never does it at a light only at intial start when warm..and the weird part is sometimes its fine...im pretty sure this is a fuel issue not a tune-up/elec issue, some have said fuel presure reg, any way it could be this????i need some feedback from you experts, i have replaced coolant sensor that feeds computer, i have cleaned TB, i have done top engine clean, fuel injector clean in fuel, dont know what the next thing to check, please help this is driving me nuts!!!!
How many miles on the car? Has the opti been changed?
Randy
Le Mans Master
Joined: Jan 2006
Posts: 6,564
Likes: 6
From: Woodstock Georgia
FPR is normally either good or bad, not intermittent, but then it was any easy check. You would have known it if there was gas in the vac line. I am tending to agree with RandyJ75 about a fuel pressure gauge and a road test. An o2 sensor should have thrown a code. Another question (easy one again), since you replaced the ECT sensor on the water pump is your digital gauge working correctly? have you had it scanned for any historic/active codes?
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Thread Starter
Instructor
Joined: Feb 2008
Posts: 170
Likes: 0
From: hopatcong NJ
yes the gauge is working fine, it NEVER does this while driving, only at intial start up when the car is anything but cold, this is not a opti problem as we have ruled this out already, the car has 46k miles on it, what would cleaning injector due to stop if leaking, there is no smell of fuel in engine bay....
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
One or more injectors could be leaking when hot and not every time. You shut off engine, injector leaks liquid gasoline, you start up and engine runs poorly due to over rich condition until the rich condition is cleared out by air passing through running engine, injector doesn't leak fast enough to hurt running engine. If it is this, then the only way to fix is to let someone with complete injector test facility that can heat the injector and put fuel pressure on it and watch to see if it leaks and keeps trying until it finally leaks. Intermittent problems are the hardest ones to find!
Heel & Toe
Joined: Nov 2007
Posts: 17
Likes: 0
From: Ottawa Lake Michigan
I just developed the same symptom. Usually only does it when started. After it is running a while, no problem. I just finished installing my 502 Comp Cam, Exotic Muscle long tube headers, and had a tune from PCMforless. So, I'm talking with Bryan Herter about it, and he thinks it is an O2 sensor acting up. Especially, since it stops after it has been running a short while. I assumed I would get a code if it is an O2 sensor but Bryan advises that an intermittent problem may not throw a code. I'm feeling pretty confident in Bryan's skills so it looks like I'm going to buy two new sensors and see what happens. Any suggestions on which ones to buy?
Thread Starter
Instructor
Joined: Feb 2008
Posts: 170
Likes: 0
From: hopatcong NJ
keep in touch hopefully we can help each other out cause im going nuts over this problem!, its my fiances car but its really bothing me! well i just replaced my coolant sensor, (the one bye the water pump) and that did nothing, so i need some advise too as to which o2 sensors to replace, i was told same thing that they will not through a code unless they are really shot..its an air or fuel issue for sure .AN SUGGESTIONS ON THE SENSORS 
Advanced
Joined: Apr 2008
Posts: 71
Likes: 0
From: Gainesville FL
the 02 sensors closest to the engine are the ones the ecu uses to make a/f adj's. The ones after the cats are to ensure the cats are there and are working properly.
Try the fuel Pressure test, and tape the guage to the windshield and watch it for a while. It should hold pressure for a while even after shutting off the engine. This should tell you if leaking injectors are suspect.
Yeah, if your temp guage (the digital one you can call up, NOT the needle one) works well, not that simple... sorry.
For the helluvit, try bleeding your coolant too.
BTW... who changed the CTS? Check and make sure that the connection is good. If it starts acting up wiggle and push the connector for that one (yes the one in the water pump). If it settles out then it's the connection. This connector can be damaged during a serp belt un-tensioning. I'm the one that messed mine up, but I found the prob so... cool.
Try the fuel Pressure test, and tape the guage to the windshield and watch it for a while. It should hold pressure for a while even after shutting off the engine. This should tell you if leaking injectors are suspect.
Yeah, if your temp guage (the digital one you can call up, NOT the needle one) works well, not that simple... sorry.
For the helluvit, try bleeding your coolant too.
BTW... who changed the CTS? Check and make sure that the connection is good. If it starts acting up wiggle and push the connector for that one (yes the one in the water pump). If it settles out then it's the connection. This connector can be damaged during a serp belt un-tensioning. I'm the one that messed mine up, but I found the prob so... cool.
Last edited by 94LT1VETTER; May 5, 2008 at 10:43 PM. Reason: Brain fart.
