code 543 help!!

[baby3848]

I have a 94 4x4 xlt 4.0l .So this is whats going on while driving one min its normal great on fuel then once in a while it suddenly speeds up and then boggs down as I watch the fuel gage drop. Checked for codes (as the cel doesnt come on??!!) I get 543 koeo as well as in the memory if I clear codes it doesnt come up until it starts acting up again what I've done so far check wires from firewall to pcm and reset they seem fine also checked relay and swaped it. Fuel pump primes at start. This has been going on for last 4 months. Could the pump be acting up like this for this long and maybe needs to be replaced. ( I always thought when pumps go they go now!) Any input would be great My husband is ready to push it off nearest cliff!!

Thanks Deb

 

[BrooklynBay]

Here is some information on code # 543:
543
(O)
Fuel pump monitor circuit shows no power - Power / Fuel Pump Circuits.
543
Fuel Pump Circuit Open–Battery To Powertrain Control Module (PCM).
(C/O)
543
(O) Fuel pump monitor circuit shows no power (M) (Service 556 code first if present) Fuel pump relay or battery power feed was open.
This information was in my thread on EEC codes: http://www.explorerforum.com/forums/showthread.php?t=160035

 

[MrShorty]

I can't ever keep straight exactly which part of the circuit a 543 points to. Basically, it suggests that there is a problem in the fuel pumjp circuit. To complicate matters, it appears to be somewhat intermittent. This means finding the fault means that the fault has to exist when you're looking for it. Best advice at this point:

Get a wiring diagram and go through the fuel pump circuit carefully to make sure there are no obvious loose/bad connections between the battery and the fuel pump. Don't neglect the ground side of the circuit. Check the fuse carefully, I have seen (though it's rare) fuses that blow, but the wire inside still makes intermittent contact.

If there aren't any obvious loose connections, then, next time it acts up, get your voltmeter out, start at the battery, and work your way down the circuit (use a jumper wire to ground the fuel pump test lead in the self-test connector). Where the voltage drop is is where the problem is.

 

[dpetree]

Similar problem

I have a 94 4x4 xlt 4.0l .So this is whats going on while driving one min its normal great on fuel then once in a while it suddenly speeds up and then boggs down as I watch the fuel gage drop. Checked for codes (as the cel doesnt come on??!!) I get 543 koeo as well as in the memory if I clear codes it doesnt come up until it starts acting up again what I've done so far check wires from firewall to pcm and reset they seem fine also checked relay and swaped it. Fuel pump primes at start. This has been going on for last 4 months. Could the pump be acting up like this for this long and maybe needs to be replaced. ( I always thought when pumps go they go now!) Any input would be great My husband is ready to push it off nearest cliff!!

Thanks Deb

I have the same vehicle, similar issues. My experience with vehicle repair is limited, but I like to take on a challenge! Let me start with my codes, explain my symptoms, and then what I have done so far to resolve this.

My KOEO codes are 543 and 332. The codes came up on my scan tool in the order 543, 332, 543. I don't know why the 543 is in there twice, but perhaps that was where things started to go wrong.

This vehicle was purchased from my dad who owned it for several years and took really good care of it. I have owned it for 2 months now. My dad mentioned an engine 'surging' problem during warm weather, and I noticed it also after I bought it from him. It was only a slight surge, so not a real problem to me - I can't say if it was severe or not as it still ran OK. Our mechanic was unable to find out the cause of the 'surging' so it has been unresolved. I also have noticed extremely poor gas mileage - around 11MPG in 2-wheel drive Then, last week the 'check engine light' came on after driving for a half mile or so. Maybe this was because the engine started to warm up or something around that time.

So, I bought a scan tool (Equus 3140) that has OBD1 connection adaptor for the '94 Ford to get my codes. The instructions said to warm up the car and then run the diagnostic. This was my first experience using a scan tool, and because I was following the computer instructions and not reading the manual first, I failed to connect something to the adaptor - not the trapezoid cluster of 4 or 5 pins, but the single pin connection off to the side of the trapezoid - I think that is called the EEC-IV wire. I started the car and ran the tests to get the codes. After reading something else online, I think I should have done the tests with the engine off, and tried to resolve that before moving on. But I didn't really know any better at the time, so I did the KOER test before fixing my problems. During this test it seemed to run a little funny for about a minute - idle was a little off, but then it slowly started to sputter and die. I disconnected the tester and it's cable from the car, but now I am unable to start the car again. It will make some engine noise like it wants to start, but it just won't kick in and make any combustion happen. There are no little pops or almost engine starts, it just spins and wont get going.

What I have done to fix this is that I tried to figure out what the solution for code 332 was. From looking on the internet for answers, I have found several posts stating the 'Differential Pressure Feedback (DPFE) Sensor and Hoses' could be the cause. So, I got this part from a parts store and replaced it today. When I did this I noticed that one of the hoses was badly cracked. The dealership was closed today, so I am not able to get the hoses from them. For testing purposes I used some electrical tape as a patch on the hose. I will be replacing the hoses with Ford parts because my parts store says they are specific hoses for high temperatures and that normal hose would not work - they also did not have any substitutions for these hoses. Anyways, I think that will fix my surging issue when I can get the vehicle started again. It was probably a cracked hose, and possibly a faulty DPFE sensor.

Now, I am struggling to get the car started! After replacing that sensor and patching the hose, I cleared the codes on the computer and tried to start it and then I tested for codes again. Again the car would not start. The same 543 code is coming up again, which has brought me to this forum.

I do have a Haynes repair manual, and the internet as a guide, and this forum response is somewhat helpful. I might just have to play with the wires and connections some more. If I really have to play with the wires and test everywhere that is OK, but I might just have to tow it to a mechanic to look it over. Is is possible that my scan tool caused the problem, or maybe I blew a fuse? Maybe my problem is an easy fix since it was scanning the vehicle when running, that may have caused some obvious damage somehow?

Thanks for anyone that can help!

 

[MrShorty]

I would not expect your scan tool caused the fault. Where you had the 543 there before, you probably had a loose connection in the fuel pump circuit that has deteriorated to the point that it won't start. For a couple years I had a "random" CM 542 or 543 (can't remember which). Then one day it wouldn't start. Traced the fuel pump circuit and found a bad connection between the fuel pump relay and the fuse. My suggestion would probably be to get a wiring diagram and a voltmeter, start at the fuel pump relay and see what the fuel pump circuit is doing.

The codes came up on my scan tool in the order 543, 332, 543. I don't know why the 543 is in there twice, but perhaps that was where things started to go wrong.

I'm not real familiar with the scan tools and how they output codes (I go with the cheapskates method using a paper clip), but I suspect the reason the 543 was in there twice is because the first 543 was the KOEO code, the second was the CM code (see my notes on pulling EEC-IV codes for the distinction between KOEO and CM).

 

[dpetree]

Thanks for your reply, and I intend on doing some more testing with the fuel pump and whatever else is along the way when I have more time. After speaking with some parts stores, I also agree that the scan tool could not have caused the problem. I do own the Haynes repair manual and it has a good wiring diagram in there. So far I have looked at (and tested) the fuses and relays but did not find anything wrong with them. Maybe it is a wiring problem closer to the fuel pump, but none of these things show any problems. So, I thought maybe the PCM was the problem, but it doesn’t smell like anything got toasted and I don't have any symptoms of that being a problem. Then I looked into the Ignition Control Module in my manual – my situation is that the starter motor is trying to start, but the engine will not turn over. According to my repair book some of the testing I did on the ICM should show connections and certain resistances within the module, but one test was a complete failure and the other was not within the range of resistance the book stated. My vehicle was starting and running OK, but then when I was testing it the engine died within a few seconds, and would not start again. I think this makes sense that somehow the ICM burned out on me while I was messing with it. I know this code is related to the PCM or fuel pump, but the PCM is related to the ICM from my understanding of it. I just don’t see what the problem is with my fuel because I can hear the fuel pump turn on and prime itself. Anything is possible I suppose. According to some other resources on the internet, I think the ICM is what starts the car (or controls the coils really) and then the PCM will take over after that. If the ICM burns out it will cause my exact situation.

What I plan to do is replace the ICM and get the hoses from the dealership this week (the hoses are for my 332 problem). I found a bargain on a new name-brand ICM on Ebay for this vehicle, so I think it is worth a shot replacing it because it is a simple replacement part, and easy to get to. If I still have problems I will mess around with the fuel pump and see if I can find out anything else and post my findings when I can.

Thanks!

 

[dpetree]

Well... it was not the ICM, as I replaced it and got the same results. Is it possible the fuel pump is dead, or is this more likely to be a wiring issue? I almost want to try and test my fuel pressure to see if that gives me any clues.

I will have to wait until it gets nice out because it is below freezing and no fun to be crawling under the vehilce in this weather.

I will post updates when I do some wire testing or find a solution.

 

[MrShorty]

In order for the fuel pump itself to trigger a 543, the pump would have to have an open/short in it -- which means it wouldn't run at all. You indicated that you can (at least sometimes) hear the pump running, which suggests to me that the pump is fine (you can check fuel pressure to verify this). If you are getting KOEO 543 while the pump is running, then the fault might be in the fuel pump monitor circuit to the PCM.

 

[Joe Dirt]

If the pump loses power, I assume that the sending unit loses power as well, and maybe that explains the dropping fuel level? Maybe it just completely loses power as a unit?

 

[dpetree]

I will verify that I have fuel pressure, and then check the fuel pump monitor circuit to the PCM if the pressure checks out. I will report back on my findings.

Thanks guys!

 

[dpetree]

I had to haul this to the mechanic because my daily driver came down with an electrical issue in the distributor. I couldn't be without both of my vehicles so I finally folded.

My issue was that the fuel pump and sending unit had become corroded. My vehicle has 141,000 miles and it was just time for these origional parts to give up. The mechanic said the forementioned parts were shorting out and blowing a fuse becasue of how bad they were. I forgot to have him show me exactly what fuse they were talking about... but that fuse was also replaced. My skid shield was badly rusted and they didn't feel that it was safe to put back on the vehicle. I will be taking that to a friend to have it sandblasted and have him weld everything back together. After that I will repaint it and take it back to my mechanic who said they would put it back on for me. The skid shield might not be that important to some people, but my 94 Explorer has a plastic gas tank, and I do take it off-road sometimes. I found out there is not an aftermarket part or OEM for this skid shield, so I have to fix the old one.

I hope this helps someone else with a similar issue. Thanks to those that gave me some suggestions. I wish I had the time to replace it myself, but I got stuck in a situation with out a vehicle so I had to take it in. ;-)