I have an 03 eco cavi with random misfire when driving at a constant speed, it seems to go away if I step on the gas a little more. It also misfires if I rev the engine to about 2500rpm and hold the throttle steady. It has the random misfire code. I have replaced the spark plugs gaped to .035, problem continued so I closed the gap a tiny bit more but still misfired. Compression is ok. Engine has about 3000 miles on it. here is a list of mods that you might need to know.

-Wiseco 8.9:1 CR piston
-Eagle Rods
-Supertech valves .5mm larger intake and exhaust
-100lb supertech valve springs
-srt-4 spark plugs
-Hahn Racecraft stage V turbo system with Portfueler and Streetrace intake manifold
-HPTuners (timing and fuel is the same as stock below boost.) (I Tried loading the stock tune and problem was still there.)

If anyone could help that would be great I am running out of ideas. I may try a new coil even though it doesn't sound like that to me. The fuel injectors were sitting around for about 5 month on a shelf so im not sure if they could be the problem. Valve timing has been checked multiple times and is ok. Thank You,

Adam

I dont have a turbo or anything so not sure if this idea will work, but I had the same problem on my n/a cav. I changed out the intake gasket cause it was a vacuum issue. but your boosted so I dont know if you have to worry about vaccuum at that low of rpm or at all

I had the same issue with my N/A motor. But what you want to do is double check your compression. One of your valves might not be seating properly. That was my issue.


GMR has got nothing on this

get rid of those SRT plugs ASAP... look into the NGK LTR7IX-11 plugs for what your running, a little expensive but the SRT plugs are too long.... trust me. also sounds like you could have a coil pack issue...

I'll have to check my valves cuz the guy messed up my valve job the first time and had to buy me a new head so I wouldnt be suprised if he f***ed up the second one too. About the coil pack issue, the only thing I can think of is that my Autometer tach adapter for the Portfueler may be faulty since it is inline with the coil pack wire. If not Ill just try a diff coil pack. Ill switch the plugs out tomorrow if they have them, I never noticed that they are any longer. Learn something every day. I have checked for a vacuum leak but I couldnt find any. Thanks for the quick help more ideas are appreciated

K so it doesn't seem to have been valves or plugs, compression is great and plugs have been changed a few times now. Everything works great while in boost with no misfires but still misfires below boost at light throttle and when car is sitting still and I rev the engine and hold the throttle steady to maintain any rpm above idle. The car also goes all the way lean and cuts out if I am between 1000 and 2500 RPM and floor it but then quickly regains fuel and runs fine again. I have not edited any fuel parameters with Hp tuners. Could it be bad injectors/short in injector harness??

I don't know if this helps trouble shooting, but don't spark-related misfires lead to a rich condition? Fuel is not burnt and gets shoved out the exaust? Your seeing a lean condition with misfires, so it's not getting fuel. Checking the injectors/connections might not be a bad idea.

oldskool wrote:I don't know if this helps trouble shooting, but don't spark-related misfires lead to a rich condition? Fuel is not burnt and gets shoved out the exaust? Your seeing a lean condition with misfires, so it's not getting fuel. Checking the injectors/connections might not be a bad idea.

This is a very common misperception. The fact is, ignition misfires and the resultant unburned fuel in the exhaust will actually lead to a LEAN O2 sensor reading, not a RICH one. Here's why:

The 02 sensor, as the name implies, measures oxygen content of the exhaust...not fuel itself. When the cylinder misfires, the oxygen in the cylinder is not consumed, as no combustion event takes place. More raw, unburned oxygen then enters the exhaust stream. This skews the exhaust's oxygen content upward, which drives sensor activity lean.

I believe we're also working with this fellow via our Tech Support, so hopefully it will be a situation he's able to correct soon. Thanks for everyone else's help too!



Bill Hahn Jr.
Hahn RaceCraft

World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com

happens to me too, but i just ignore it.. when i push the clutch in to come to a stop i get real rich for a few seconds, < 10.0, so i give it gas and it goes back to normal. not sure if i took fuel out of the coastdown table if it would help or not.. but eh, the light goes off after 5 or 10min so i just ignore it



12.33 @ 111.67 mph [Oct 2009]
Dyno'd on 08/02/09 - Mustang Dyno:
327.6 WHP 333.6 WTQ [10.1 AFR]

Vincent Morris wrote:get rid of those SRT plugs ASAP... look into the NGK LTR7IX-11 plugs for what your running, a little expensive but the SRT plugs are too long.... trust me. also sounds like you could have a coil pack issue...

SRT4 plugs are a great plug to run... I and several others ran them for years with ZERO issues... How many issues can you document where the plugs caused internal damage?



LE61T PTE6262 Powered

I didnt have good results with the SRT4 plugs, the engine just felt really flat, I ran better with stockers and the MSD



1989 Turbo Trans Am #82, 2007 Cobalt SS G85

Check for vaccum leaks. Like around the injectors or the injector cups that are in the head. Maybe spray some carb and chock cleaner around the intake manifold and the injectors. If the car stumbles or dies that would be a vaccum leak. Maybe try a new map sensor..

Tomorrow is my day to figure this out. Im installing my EBC and try to figure it out again. If i still cant figure it out maby they will be able to figure something out when I bring it to HAHN for tuning even though I doubt it is the tune. I will keep everyone updated, thanks for the quick responses and I am the same person form the tech support, Thank's Bill.