A9M with Trouble Code 18

[lars]

I realize it sounds frustrating, but I'd still be chasing that code 18. If there is a misfire, that could be what's triggering it.

Also, during a Key On Engine Running test, you can trigger a cylinder balance test that zeros in on specific cylinders. It's been ages since I've run one so I don't recall the steps offhand but it's not difficult.

 

[Timmy390]

I read someplace the Chilton manual has the steps..... Maybe?

Tim

 

[BanditBronco]

I would spin around once, take a deep breath and start from the top. Easiest to hardest. You have been in it long enough now that your brain is canceling out the easy stuff you have checked 20 times already. I would definitely invest in an O-scope so you can at least see what the tfi sensor is doing. I know I have a few Ford TFI's left over from my yearlong endeavor of chasing my tail. I might still have a computer, let me check. Not that I am on the shotgun parts team but at least you can ease your mind by checking it off the list.

I agree with Lars, computers don't throw codes for no reason. Even at this time in computer technology, just because the issue isn't directly related to the code description something in the ignition circuit is not within spec.

 

[Past_Miner]

I realize it sounds frustrating, but I'd still be chasing that code 18. If there is a misfire, that could be what's triggering it.

Also, during a Key On Engine Running test, you can trigger a cylinder balance test that zeros in on specific cylinders. It's been ages since I've run one so I don't recall the steps offhand but it's not difficult.

My code reader will run the cylinder balance test. That one is easy. It doesn't miss at idle though. Most of the time it happens at a steady cruise and almost never under heavy acceleration.

At least it starts every time now. That makes diagnosis much easier.

Sent from my SM-G991U using Tapatalk

 

[BanditBronco]

If you clear the code, how long does it take to come back? Can you clear it and then COEO and it comes right back or do you have to COER to get it to come back?

 

[Broncobowsher]

Pull the distributor cap and check the rotor. And the inside of the cap for carbon tracking.
Just looking for ideas that might be outside of the computer.

 

[stupidboy]

Is it possible that the wire that were shorting out have burnt something out in the pcm?

 

[Past_Miner]

I wanted to close this out. I finally just bought a new EFI harness and went through the whole install again. The problem is gone. I still have a few minor issues but I think it is all timing and plug wire related.

The problem is clearly in the harness somewhere. Someday, when I have lots of spare time, I will probably unloom it and rebuild it from end to end. I suspect the blue wire that is normally in the shield with the SPOUT wire is also shorting out and causing the problem.

 

[DirtDonk]

Thanks for the update. Hope it's a more permanent fix than you had in August where it started acting wonky again after a day or so.
But here's to crossing fingers it's all gone and just fun ahead.

Lot of work, and a pain, but doing it over from scratch seems like it was the best course of action.
Which harness did you go with? Change anything else?

Paul

 

[Past_Miner]

Thanks for the update. Hope it's a more permanent fix than you had in August where it started acting wonky again after a day or so.
But here's to crossing fingers it's all gone and just fun ahead.

Lot of work, and a pain, but doing it over from scratch seems like it was the best course of action.
Which harness did you go with? Change anything else?

Paul

Well, it wasn't a more permanent fix.

I chased the problem for a few more weeks and then stopped for the winter. In the end I finally pulled the computer and opened it up. It did indeed have a failed capacitor. I have a fresh rebuild in now and will repair the old computer myself this summer for a spare.

Almost everything is back to normal now but I have a very faint and very frustrating intermittent misfire that I am chasing. It only occurs at low throttle cruise on the road. TPS tests good and I don't get any codes except the normal emissions codes. I even got the coveted code 11 last night. Cylinder balance test also shows no low performing cylinder.

I am suspecting a bad plug wire or plug from all of the previous dead cylinder issues, but I am always open to suggestions if someone else has solved this problem. I will probably post a new thread if I can't get this fixed this weekend.

DirtDonk - I went back with the Ron Francis harness, basically the same as the old RJM harness. Still a A9M computer.

 

[onpier55]

Make sure your injector plugs are in tight. I had an intermittent miss when #1 injector backed out and would make intermittent connection. I pulled the rubber seal in the plug and it made good contact. Ordered new locking inj plugs from rock auto. Drove me nuts. Changed plug wires. Fixed vacuum leak at Pcv. Frustrating. Runs great now. Good luck. Mine is an EDIS system.

 

[Past_Miner]

Make sure your injector plugs are in tight. I had an intermittent miss when #1 injector backed out and would make intermittent connection. I pulled the rubber seal in the plug and it made good contact. Ordered new locking inj plugs from rock auto. Drove me nuts. Changed plug wires. Fixed vacuum leak at Pcv. Frustrating. Runs great now. Good luck. Mine is an EDIS system.

I will take a look at the injector connections. I don't have anything to lose from that.

I pulled all of the plugs last night and tested all of the plug wires. There weren't any obvious signs of a bad cylinder from the plugs and all of the wires tested good. I put it all back together and ran KOEO and KOER tests. Only got the normal emissions codes: KOEO: 81, 82, 84, 85 and KOER: 33, 44, 94. No continuous codes.

I ran the cylinder balance test three times in a row and got a clear test all three times. It ran great on a test run last night, never missed once. This morning I let it warm up for about 10 minutes and it had that same misfire on the way to work. It seems to go away after the engine gets really warm.

A bad O2 sensor should throw a code and a light, but I have read of people with this problem that found a bad one without either. I hate to throw parts at it but I'm running out of options.

 

[Timmy390]

This morning I let it warm up for about 10 minutes and it had that same misfire on the way to work. It seems to go away after the engine gets really warm.

I had this issue right after my rebuild. Tried everything. Ended up being a bad set of plugs. I ordered them ONLINE and I must have gotten knockoffs/counterfits.

I figured it out once a plug completely died. I change that one plug...ran fine for a few weeks then started acting up again. Figured it out when another plug died. Bought a new set and it's been fine since.

Tim

 

[Past_Miner]

I realized that I never closed thread out, but I did eventually solve the problem.

It is a long story, including repairing the old computer, swapping computers back and forth a few times, changing plugs, changing plug wires, confirming grounds, adding grounds, etc., etc.

I finally checked all of the big battery wires for continuity - battery to battery isolation switch, switch to block and, block to firewall. All checked good, except the resistance across the switch seemed a little high for a closed battery switch. When I wiggled the switch handle, the connection would occasionally break. It didn't lose every time, but sometimes. I swapped out for a new switch and I haven't had a misfire since. It has been running like it did for the first 16 years for about 9 months now.

I am assuming that vibrations from driving was wiggling the switch contacts slightly and that sometimes it would break the ground and cause the computer to hiccup. It's just proof that you need to stick to the basics with the troubleshooting. Grounds - always check the grounds on EFI.

Thanks again for everyone that commented to help on this one.

 

[DirtDonk]

Hey, thanks for bringing this back around and closing it up. Good to hear it’s been working.