Hi all, I have a large problem that I need help with. My car was put away for the winter and I was doing some work on it. Fixed some rust which I'll start a new thread on soon, installed coilovers, put new coils in because on occasion I would get restricted performance and random misfires, although the car usually ran fine. New Denso plugs were installed 4 years ago.

After installing the new coils, I reset the electrical system, hooked up the battery which has been on a battery tender all winter. Start the car and it's running very rough. I get codes P0353,P0355, and P0358. I thought, maybe the new coils are a problem so I replaced those 3 cylinders with the old Denso coils. Same result. I got some Beck Arnley coils thinking the Chinese ones I got might be bad. Replaced the 3 misfiring cylinders with no change. Decided to get some new plugs to see if that's the problem. No change. I took the ECM out and checked it with a magnifying glass and saw no problems.

I just did a compression test to make sure the engine is ok. From cylinders 1 through 8 I got 125, 127, 130, 130, 120, 122, 122, 125.

I'm not sure where to go from here. Any thoughts?

 

Air leaks and injectors can also cause misfires. Can you read the fuel trims?

 

I thought about that but I can't find my regular scanner. I don't know where I put it. I'm using Torque pro to read codes. Does that do fuel trims also?

 

I would guess that you have a wiring malfunction. The dtc's you've got suggest an open or short circuit between ECM and coils.

so i would start with checking the wiring for obvious damages and measuring resistance between pins.

Fritz

 

Yes you can read fuel trims with Torque Pro

 

Hi johns55,

Here are the P0351 definition and some possible causes from the DTC Summaries manual which apply to all of the P035X codes:




The most common cause is that the coil electrical connector is not fully seated/connected. Inside the harness half of the connector is a rubber seal, a sort of rectangular O-ring that normally fits in the deepest recess of the connector to seal out moisture, oil, etc. Sometimes these seals deform or become dislodged when the coil is disconnected, making it difficult to fully seat the two connector halves till they latch. It would be worth having a good look inside the harness connectors for cylinders 3, 5 and 8. Here's the chart for your cylinder numbers:




If all the connector seals seem properly seated the same as the ones on cylinders that are not misfiring, and the connector halves are latching together properly, the next thing might be to check for damage on the insulation of any of the coil wires. The insulation becomes brittle with age and can crack and allow bare wires to short, or to allow the copper conductors to break.

On most AJ-V8 engines the coil wires are cut to length and taped into groups so they can't easily be connected to the wrong coil causing an incorrect firing order, so I doubt that is your problem.

In case you don't have cylinder-specific problems but a broader problem that is manifesting in cylinder-specific codes, it might be worth cleaning the ground points referenced by the ECM (EM1 in the engine bay right hand enclosure) and the ground referenced by the coil ignition modules (EM2 in the left hand enclosure):




I assume you don't have oil in these three spark plug wells or you would have mentioned it. That generally triggers P030X codes anyway.

Are the plugs gapped correctly and of the correct type? A quick search shows that depending on your VIN, the OE plugs are NGK PFR5G-13E or PFR5G-11E. Using the NGK iridium equivalents is fine, but using other brands can be hit or miss (pun intended).

Are there any other DTCs flagged in addition to the three misfire codes?

Cheers,

Don

 

Thanks very much DonB for the detailed info. I have checked as well as I can, all of the connectors and they look fine with no breaks in the wires. The plugs I replaced were Autolite XP3924. No change with these installed. I have just tried to check the fuel trims with Torque pro and an open circuit message and unable to read fuel trims message. I need to sort that out first to make sure this isn't a fuel problem. I may also try to check the fuel pressure.

 

Ok, just found my regular scanner. It shows the same codes and problems that Torque Pro shows. It can't read fuel data showing open circuit. I hooked up my cheap Harbor Freight fuel pressure gauge. I get 38 psi and when I give it a little gas it goes down to around 33. Could this be a fuel pump problem or possibly fuel regulator?

 

Yes, and it could also be the fuel filter. Has it ever been changed?

 

Yes, this car has been taken apart and put back together New fuel filter and gas lines from tank to filter about 3 years ago. Maybe 10,000 miles ago. Sprung a gas leak on 3rd Ave and 42nd St in NY. Found out the gas lines had rusted out in the past and was replaced with rubber lines which broke. That was a fun evening.

 

Ok, so I really need some help now. As I mentioned before, plugs and coils have been replaced. Checking the fuel system I get 40psi key on, 38 psi at idle and around 35 psi at 2,000 rpm. That seems a little low to me. I am trying to read the fuel trims and I get fuel system open loop failure. Both of my scan tools will show no fuel data.

I let the car warm up to temp (still misfires and runs rough) and check again. Can't get any fuel data, open loop fuel system failure. I'm not sure where to go from here. I could change out the fuel filter even though it only has about 10,000 miles on it. I don't know if there is a problem with the fuel pump. I checked the fuel regulator while I had the fuel pressure tester hooked up. 38psi at idle and unplugging the vacuum line it went up to 43psi. Seems like the fuel regulator is working. Any and all help would be appreciated. I was hoping to take the XK8 on a trip from CT to Florida next month. That won't happen if I can't figure this out.

 

Since you can't get out of open loop, I'm wondering if the problem is with the air and water temp. sensors or MAFS. Are you able to read the real time values on your scan tools? Have you checked the coil circuits back to the ECU as Fritz suggested?

I'm beginning to suspect a ECU problem.

 

If it won't go CL (closed loop), yes, check sensors, including O2s.

You've something really badly wrong when it won't go CL.

 

Yeah, something is very screwed up. I don't know how to check the wiring for the coils. I did use my multimeter to check the injectors and they all checked very consistent at 16.1 ohms.

 

I doubt that dubious coils would prevent CL.

If you really want specifically to test coils there are testers but I think your problem is elsewhere.

 

Yes, I don't think the coils are the problem. I just don't know how to check the wiring or ECU.

 

I thought I'd update the thread since I've been away a while. My problems with the car have gone from bad to confusing. Cylinders 3,5, and 8 showing misfires after coil change. This is what I've done so far.
1. Swapped the coils in 3, 5, 8 with another set of new coils. Same result
2. New spark plugs even though the ones installed only had about 20,000 miles on them, Same result
3. I installed a re-manufactured computer from Foreign Auto Computer repair. Same result
4. Got an engine wire harness from a salvage yard. Installed and same problem

I can't read the fuel trims because I get open loop fault and nothing is shown.
The only thing I have not replaced is the fuel injector. Any thoughts?

 

Hi John,

I can't remember if you ever confirmed that there is no oil in the spark plug wells. I also can't remember if we discussed the engine ground strap, which is the ground path for spark. It's worth disconnecting both ends, cleaning the bolts, washers and eyelet terminals thoroughly with a small wire brush and zero-residue electronic cleaner spray, allowing to dry, then reassembling and snugging but not overtightening.

My next thoughts are to confirm these cylinders are getting proper signals to the coils and injectors. You could get a basic idea with a noid lamp or a multimeter that can measure duty cycle or pulse width. Even better would be to have the system analyzed by a knowledgeable diagnostician with a Picoscope or other good automotive oscilloscope.

A step you could perform yourself would be to disconnect the ECM connectors and test for low resistance and no shorts to ground in the wiring between the coils and injectors and the ECM.

Cheers,

Don

 

carefully undo the pins that hold the coil wires along the valve cover and slowly separate the wires. three cases, my car being one of them, the insulation is hard and brittle allowing the coil wires to short against each other. any moisture only enhances the effect. this will often destroy the coil. seems to affect right bank, number two most often and might be the unknown cause of the common ignition code. note that the wires often look acceptable until disturbed. mine are temporarily taped until i build new coil harnesses. the number two was so bad that where it makes the turn to the coil jack pieces of insulation were flaking off, of course where the wires crossed each other.

this is a high heat area and probably requires wiring that is more durable. their mistake was not sealing the well with a coil pack seal and having an open setup with waterproof wiring and packs as seen in the Japanese and LS engines. the heat stays inside while the water gets in. i stenciled on both coil covers, "NO WATER," in case someone decides to be efficient when i am not around or does not listen to instructions. when i was playing with the garden hose after the radiator replacement, one little drip down the right cover highlighted this failure and shorted a brand new coil. it seems like the water easily gets past the cover at number two. perhaps people with persistent coil codes at this one need to unwrap the harness.

 

had to tape up my coil wires about 2 weeks ago due to insulation falling off and spurious misfires/lean codes, and although OP replaced engine wiring harness, it might be worth a second look.