Hello again all, and thanks for the help I’ve gotten in the past from the forum.

My last round of issues centered around “engine failsafe” codes and turned out to be the brake switch. I had a concurrent issue, which seemed to go away with that fix, but has come back with a vengeance.

“Restricted Performance” with the yellow warning light and check engine light. Sometimes a flashing check engine light. It started only occasionally, and would clear up in a few hundred yards, but progressively got worse. Lately it happens almost the moment the car is started, and got to the point where it might stay stumbling and running on less than 8 cylinders for several miles. Once it cleared up it was gone, except last Friday, where it came back once I was on the interstate.

It comes on like a light switch, and goes away the same way. The engine either runs rough, or runs great. I did notice the harder I tried to drive with the stumble, the more likely the flashing check engine light would start.

I have replaced the fuel pumps a year or 2 back, and I replaced the plugs and air filter this Spring I think, with no issues after either maintenance. I do have leaking valve cover gaskets, with a slight amount of oil dripping onto the exhaust manifolds and smoking off.

With the car idling and the stumbling and “restricted performance” light present, I can clear codes and the stumbling stops for a second before returning. I can do this over and over, but the stumble always comes back immediately.

The codes I’ve seen are:

P0302
P0306
P0307
P356
P357
P1000 (after clearing codes)
P1111 (normal)
P1314 (bank 2)
P1316
And on reader “fuel sys 2 OL fault”

The codes can come in several combinations, generally 3-5 at a time when I have cleared them. This is a comprehensive list of all that I have seen.

I have a reader that can view live data and store it, and I have data sets stored for when things are running well, and with the stumble, so if you ask me for some data on that list I can give it to you for both scenarios.

Today I had the P0302 and P03036 codes predominately, so I pulled the coilv #5 and #6 coilpacks and swapped them. The stumble went away and I took a drive up and down the interstate. When i got home I read the codes again and it showed a P0307 and P01316 code (plus P1000), even though everything seemed smooth.

Can anyone give me some advice on what to check now, or enlighten me to what might be going on? I drive the car hard (WOT) on a daily basis, and have never had any signs of low fuel pressure or fuel starvation, FWIW. I only buy gas from 2 Shell stations, use the same pumps, and only use 93.

Thanks,

Mike

 

Check the battery. It should read at least 12.4 after sitting overnight. Also check it with the engine running, 13+. If that is okay, start checking the all the power connections and grounds.
Low voltage causes many strange codes.

 

That was brought up during some of my previous troubleshooting, and I tested the battery and the usual ground problem areas and all checked out OK. I also ran the XJR off a brand new battery before (was for another car of mine) and it didn’t solve anything.

I’m pretty sure it’s either an ignition (or possible fuel) issue, and not a flaky battery. Especially since I just made it go away by moving coilpacks around. My daily commute is ~35 miles roundtrip with maybe 2/3’s of that interstate, so the battery stays well charged.

I appreciate the suggestion though,

Mike

 

FWIW I checked the voltage after sitting for a couple hours and got 12.5x from battery positive to a chassis ground (not negative terminal).

I just ran to the store (4 miles roundtrip) and ran seat heater, AC, lights, and radio with no stumble and no codes. Left it in 2nd and took it to 5k rpms at one point with no issues.

Mike

 

Couple of hours isn't long enough, try after 12.

Otherwise you may have an O2 sensor fault that's causing misfires to flag but if not then so many misfire codes... which comes back first?

 

Is there any oil in the plug wells? Might retorque the plugs, and check the seating of the coil packs. I would also check ground straps for breaks causing intermittant interuptions. Maybe check the seating of plugs to the ECU.

MAF sensor and throttle bore cleaned; maybe clean the injectors with fuel system cleaner . . . all guessed out