Install the ECU and drive the car and see what takes place. You are upset and ustng a shotgun approach see what takes place.

Gus
www.jagrepair.com

 

Not shotgunning. Used process of elimination up to this point. They found no problem with the ECU and I had already reseated the connectors so there is no reason for the problem to go away just from removing it and reinstalling it. I fully expect the problem to manifest itself exactly as before I sent it off.
I'm thinking there may be a problem with more than just one coil but for some reason the ECU is reporting it as cyl 8.
It still doesn't seem like a fuel injector problem to me either as I've never seen one temp sensitive before and slowly fail as it warms up and then fix itself when cold.
Doesn't seem like a sticky valve problem either.
If it was a tensioner problem it should do it all the time and also on the entire bank.


Dave

 

Swap a different coil with #8. If it still reports #8 then it's something to do with #8 but you haven't figured what yet.

 

Dave, had same problem with my 00. Mine turned out to be a vacuum leak at the TB connection for brake booster hose. Very hard to get to without removing the TB, previous owner used some shrink tube to repair a cracked hose. Connection has a o-ring that is notorious for failing. Good luck

 

Already did that multiple times, always cyl 8.


Dave

 

Did it present as a single cylinder misfire (P030X) and a P1316 and only fail after a warmup?


Thanks,
Dave

 

Yes it went from no cel to misfire at all eight cylinders after rinsing engine, with a waterhose. Thought maybe I had water in the down in sparkplug cavity. No water but did have some oil down there. Changed gaskets, changed plugs, helped but still had p0308 and p1316. I must have hit the repaired vacuum connection while I was rinsing engine. Repaired hose connection and haven't had a cel yet.

 

So the hose was the fix?

 

Yes I was still getting the p0308 after replacing gaskets and plugs. The P0308 didn't come on till I drove the car about 3 to 4 miles, started running progressively worst, with hardly any braking power.

 

That awkward braking was a clue to lack of vacuum. Good to hear it's fixed!

 

My braking still seems normal. I am waiting to get my ECU back Mon or Tue and also have an injector on order coming around Thu.
I did try spraying carb cleaner around to see if I could find any vacuum leaks and couldn't but if the leak was way under the intake or deep in back of the engine I wouldn't have found it.
I will examine the hoses and connections again though if the injector doesn't fix it. I just hope I don't have to pull the intake to do it.

Dave

 

Just now got the ECU back from ASI. As they found no problem with it I will not even bother starting the car yet until the fuel injector arrives later this week and I install it. Since the car as been sitting more than 3 weeks there should be little or no pressure left in the fuel rail by now but I will check at the Schrader valve to be sure.
Also its been raining everyday pretty much all day for more than 3 days now so I can't do anything until the weather clears up anyways as I have no garage or carport etc.


Dave

 

What I have done so far:
Replaced all spark plugs.
Swapped cyl8 coil twice.
Swapped ignition modules.
Sent the ECU to ASI and they found no problem with it.
Put BG44K in tank but can't drive it long before it gets CEL then Flashing CEL/Restricted Performance.
Cleaned MAF and Throttle body, twice.
Sprayed Carb Cleaner around intake and hose connections I could get at. No obvious leaks.
Replaced the fuel filter in case I had gotten a bad tank of gas that plugged it up. The old filter only had about 600 miles on it and looked clean inside.

Today I am replacing the cyl 8 injector but I suspect that isn't going to fix it either.

Dave

 

A couple things to consider.
On cold start the ECU is not fueling based on the response from the O2 sensors in the exhaust, they aren't up to temp and functioning. It's operating on throttle, temp and a little input from the MAF. Sort of like an old engine on a choke. When it warms up to 70-80 Deg. C, it begins entering closed loop and fuels based on the exhaust. That can explain the 'good running' until some warmup.
Second, there are cases where some sort of air or vacuum leak is not troublesome until things warm up. A fracture in the induction plenum in the vicinity of the #8 intake valve could get worse as things heat up for instance. It's even possible for an intake seal to be leaking or split, and let more unmetered air in the hotter it gets. Put that together with the first idea and things get compounded.

It's also still possible to be related to the ECU. But it would require an oscilloscope and someone very competent with it to confirm that.

You have done a good job with your diagnostic path, but you are at a spot where I think you're gonna need some higher tech assistance.

Good luck!

 

I sent the ECU to ASI and they bench checked it and said it was fine. It had failed before a few months ago and they repaired it and was still under warranty. It seemed like it could be an ECU problem but they says they "extensively tested it" and it was fine.

 

Understand.......

But there is no testing like real world testing.

 

I do have an oscilloscope and more than 40 years experience using them for troubleshooting computer and home electronics problems. 29 years as a computer engineer at Motorola. Since all the signals are low voltage to the coils and injectors I could compare signals between cylinders and see if the cyl 8 signals look different. My problem is I have no garage, carport or paved driveway to work on the car.


Dave

 

What I would be interested in is the coil current vs #1 injector voltage as the trigger. See the attached. This was done with a low amps current probe clamped on a single loop in place of the ignition coil power supply fuse. In particular I would want to see the current ramps as the misfire rolled in during warmup. If the #8 cylinder current ramp remained the same as the others, I'd be good with the ECU. That would leave you with an engine mechanical cause, something like an air leak in the vicinity for #8 cylinder, or the #8 injector.

You could also move your wire loop to the injector supply fuse, and check the injector current ramps in the same way.

Cheers,

 

As I already purchased a replacement injector I think I will try that first. Was going to do it today but ended up helping someone with a computer problem much of the day and then a Doc appointment so most likely I will try that in the morning. If that doesn't fix it then i will look for vacuum leaks again. I tried spraying some Carb Cleaner around the cyl 8 area and at some hose connections I could barely see but didn't find anything obvious but I will try that again also.


Dave

 

There can be an air leak on the valley side of the induction plenum. You will never see or hear one there. Many times I've had to eliminate down to such an idea, then reseal the intake, or replace it based on that. Only one time did I not repair the car after going through all that.

The same thing goes for the 4.2L engine. Many times bank 1 fuel trims are +10% or more and can't find a reason. Remove the plenum and install new gaskets......problem fixed.

Good luck!