Misfire problems
 

After a couple of days troubleshooting this I'm throwing it over to the brains trust.

Things were just going too well in the lead up to the IM240 test and my L98 (think LS2 if Stateside) has decided to throw multiple fault codes on cylinders 2 & 4. The engine goes into limp mode and runs extremely rich as a consequence. Engineering process has been halted and the clock is ticking.

The engine was making plenty of power until about Tuesday this week when I noticed a drop in power and rough idle part way through a test drive. This is a new crate motor with maybe an hour of running time and no abuse or obvious signs of damage such as smoke, noise, etc.

Codes picked up by the scanner: 202 & 204 (cyls 2 & 4 injector circuit malfunction/open), 300 (multiple cylinder misfire), 302 & 304 (cyls 2 & 4 misfire), 1381 (misfire detected). Plus others that are unrelated such as no comms from BCM.

The following tests have been conducted, the ECU reset and each time the codes come back after a short drive.

• Swap injector 4 with injector 8, fault stays at injector 4
• Swap coilpacks 2 & 4 with units from another car
• Swap leads, plugs
• Noid light shows injector plug working, flashes faster on accel
• Compression test cyls 2 & 4, both around 175 with hand held tester (minor leakage possible)
• Remove, apply compressed air and reseat both ECU plugs to engine loom
• Continuity test of coil pack wiring harness, OK
• Spark plug lead tester shows good arc

If you have any questions or suggestions please post them. I expect a few Ford vs Chev jokes but may not take the bait as I'm pretty over this little 'problem' right now. ;)

Thanks

Paul

Ohh Sambo you are leading with your chin............it's Sooo tempting to kick a man when he's down.............but givin' your choice of power plant a flogging won't help ya :)

We all have these probs Paul. Ford or Chev. In my case it was the computer. Hope you get it sorted quickly. It can be quite depressing.

Merv, I have another ECU on the way thanks to doubledip.

Do basics first, you are thinking too deep
 

Sambo You are over thinking the problem Start #2 and 4 are dead
Pul;l valve cover and make sure the rockers are working to those holes
compression test next looking for min of 150 after 4 complete cycles
If compression is good go with fixing 1 cylinder at a time
Get new spark plugs for 2 and 4. See if you have a miss Test at idle and at 1,500 rpm.
Next swap injectors with good ones from other holes If missfires follow these injectors, replace. If 2 & 4 are still acting up Quad driver in ECM is bad. Also recheck the fuel fuse for injector driver.
If 2 and 4 are still not firing look at the new plugs for being wet or dry.
If wet you have either bad injectors that are leaking or dry not letting out the fuel.
It sound like you got bad fuel in the system but all injector would be having a problem.
What size are these injectors?? Are they low or high resistance ones? If you install the low ohm ones in a high ohm system ,you will burn out the drivers in short time. Have seen this happen. Weakest drivers go first.
Any way for you to do an injector flow test?? This would also tell alot about what is going on.
After you get this fixed you will need 2 new O2 sensor to have the motor running right. All that gas and running rich will cause wrong readings on the motor. Rick L. Ps Do you have the camshaft with the swap in this motor?? It's possible you have the wrong spark firing order?? I think it was a #4 & #7 swap. Do basics first to remove these issues. I have seen bad crate motors. SO don't over look this issue either.

injector plug wiring maybe? leaks on manifolds?

just thinking logically some more...

definately worth pulling the rocker covers and having a look-see as Rick suggests.

this info is gold if accurate...surely its a warm-up/heat related issue then....
whats the longest you drove this engine with no issue seen?

if you've swapped the injectors from 4 to 8, what remains? Fuel-rail last-mile (almost zero chance), injector wiring/earth, ECU, valvetrain (pull rocker covers and turn engine over by hand), manifold gaskets, spark plug-seat thread (depending on compression tester used this may not show up in a compression test).

Are your headers completely custom, or are they a design known to work on other LSx? One-off's flow direction to o2 sensor would be largely unknown.....

just thinking out alound sambo!

Ben

Good news that Doubledip is on the case as well. Great support.

Hope you get sorted swiftly Paul.

Cheers

This is what the forums are supposed to be about. Well done guys & best of luck.

I assume that the fuel filter is OK Paul. I am not sure if you have a regulator. Probably not. Unless it is a major failure of the motor, which is doubtful, it does sound electrical though. Mostly these things are something minor and not major.

A collapsed lifter or 2 perhaps when warm !??

Hi Paul, I had a problem with low power and found one of my plugs had a crack in the insulator. (But you said you have replaced plugs).

I found this by lying under the cobra with the engine idling (on stands of course) in a dark garage and saw the sparks external on the offending plug. (might be worth a try you never know).

I'd also double check all of your earthing points as that can give weird problems too.

Good luck

rgds

Gregg

Your P0202 and P0204 codes tell you there is an abnormality in the injector circuit. The injectors are nominally 14 ohms, if the driver circuit is faulty, you'll be replacing the PCM.

Being adjacent cylinders, you could have the injector ground circuits shorted together within the loom for cylinders 2 and 4.

Check the earths are tight and havnt vibrated loose with the test drives.

May not help, but my LS1 had a lead that would back itself off the spark plug after a couple of minutes driving, make sure the lead is pushed all the way on.

Couple of bad connections\pins on the ecu plug?

Thanks heaps everyone, a few more suggestions that I'll take up while I wait for the ECU. Will report back any findings.

Good news, the car is running properly again after replacing the ECU. Now to rebook the IM240 and get through engineering by end of June. :D

Good news Paul. It seemed to be converging on that being the problem. Are they expensive?

Bet that was a relief. Glad it has been resolved.

Cheers