I swear to Cthulhu sometimes I HATE my truck ... Been fighting this thing so long, lately the problem being random/bucking and jerking at cruising speeds and sometimes dies at idle. Running errands today and it dies at idle. I let it stay dead in KOEO and pull into a parking spot and run codes. Up until today I have not gotten any codes but today I got 543 in continuous memory - AGAIN. I dealt with this **** two-three years ago and it ended up being the fusible link near the battery itself, for the BATT + to fuel pump relay circuit. Two inline fuse holders were installed and the truck was ok after that. I checked those fuses, they are intact. After I restarted the engine I wiggled those wires and the rest of the harness and nothing, the truck did not die.

Also, after it died today I parked it, got out and listened to the pump, it was making a low growling noise and did NOT sound good. I got the code and cycled the key, it then sounded normal, like a high pitched whine.

If the truck ever dies I cycle the key off/on and it always starts. At freeway speeds it will randomly buck/jerk and lose power. Tach signal is always there, I try to give it throttle and there is no response and usually after a split second BOOM the truck thunks and I got power back.

So, what I have already done is, as per my last post, I have installed a rebuilt Cardone PCM. Recently I swapped the fuel pump relay and PCM relay for new BWD parts. Nothing has worked. I will be checking wires as soon as I can but what else can I look out for? Getting very frustrated with my truck, once I fix something, another problem will show up. Any thoughts?

 

From what I have read on this, it seems like replacing the fuel pump relay has usually been the remedy. Is the power distribution box in need of cleaning from dirt or corrosion?

As far as the bucking and jerking etc. When was the last time the truck had a tune up? Also, maybe the timing needs to be checked.

 

I mentioned in the initial post that the fuel pump relay is brand new, there shouldn't be a problem with it. The timing is 10* BTDC, no problems there. It had new Motorcraft plugs and ACCEL wires/coil/cap/rotor two years ago. No, I'm almost positive this is a fuel issue.

 

Bump. Any help at all is appreciated.

 

I would be prone to check those injectors. Whats your history there?

 

No idea, when the truck does run it runs smooth, not overly rich. Don't think the injectors would cause this code though ...

 

Well, you did think it was fuel related. A lot of short runs leave residue which accumulates over time. Sometimes codes are generated in response to a slightly different symptom. I had the same symptoms of jerkiness on my 97' F350 diesel and they went away after a tank of injector cleaner; not that i am advocating that in your case. You might be better served with an injector cleaning if you decide to pursue this route. Hope you find it to be an easier fix, just wanted to provide a different perspective. Cheers!

 

Bump. No updates to offer but I'm headed to a shop later this week that's helped me in the past.

 

Code 543: When the PCM commanded the fuel pump on, voltage was not detected on FPM.


Since this is in CM that means it happened at least once at some point. I know you clear the codes so I can assume this happened sometime in recent past.

Has the truck stalled while driving?

You have changed the relay, but on this vintage truck they have a habit of building up corrosion on the under side of the relay socket.

If that checks out verify Pin 8 on the PCM connector has good contact and the circuit is intact. In a previous post I found out some of the early EFI truck do not use that Pin/signal. By 1991 I believe yours does.

 

Yes, it loses power when driving. It sometimes stalls at low speed and otherwise 'runs out of gas' while cruising. Usually have to cycle the key if it dies to get it to come back.

 

Definitely take a look at the relay socket(s). If they are clean, next place I suggest to look is the ignition switch.

 

As in the key lock cylinder or the one further back in the column, the actual ignition switch?

 

Yes, the ignition switch.

 

Ok, will check that. Only other thing I can think to add is that most of the time I don't have the mentioned problems following a cold soak on the way to/from work, seems more frequent on warmer days and if I am making multiple trips, starting the engine several times.

 

Bump. Problem is getting worse, haven't had time for further troubleshooting as of yet. I booked time on Friday with my old mechanic to get some help, I can't make it .5 miles to the grocery store without the damn truck dying. It is also throwing continuous code 556 'primary fuel pump circuit failure' in addition to 543. Does that narrow down possibilities?