Engine stumbling under part-throttle (5.8)
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Engine stumbling under part-throttle (5.8)
1994 5.8. The engine idles ok and the vehicle accelerates fine at full-throttle, but has a fairly consistent stumble/misfire under partial throttle (cruising speed). It is much more violent than just a single cylinder, it feels like the the entire engine is randomly getting switched off and on.
I have replaced the plugs, wires, cap, rotor, fuel filter, coil and tps with Motorcraft parts. I made sure that the plug wires are not in a position to cross-fire. The ICV tests ok. Fuel pressure is good and the fuel pressure regulator is functioning normally. I had some generic codes last time I checked, though I'll test again soon.
I took it in to the dealer today and they called a few hours later, telling me that they could reproduce the issue but did not know what was wrong. They suggested finding a good independent Ford shop and did not charge me anything to look at it
Any thoughts? My best guess at this point is the ECU, but I hate just throwing parts at it. I also had a link to a company that tested ECUs for $75 and rebuilt them for $150-ish, but I can't find the link. I'll keep searching on that.
Dave
I have replaced the plugs, wires, cap, rotor, fuel filter, coil and tps with Motorcraft parts. I made sure that the plug wires are not in a position to cross-fire. The ICV tests ok. Fuel pressure is good and the fuel pressure regulator is functioning normally. I had some generic codes last time I checked, though I'll test again soon.
I took it in to the dealer today and they called a few hours later, telling me that they could reproduce the issue but did not know what was wrong. They suggested finding a good independent Ford shop and did not charge me anything to look at it
Any thoughts? My best guess at this point is the ECU, but I hate just throwing parts at it. I also had a link to a company that tested ECUs for $75 and rebuilt them for $150-ish, but I can't find the link. I'll keep searching on that.
Dave
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From: Easton,Ks
The way I test a ECU (aka PCM) is to go to a salvage yard and pick one up that fits your truck for $50.00. Then unplug yours and plug this one in. If the truck runs the same you know it is not the PCM or if it fixes it then pull your old one out and if this one is the same put it in. If it is just close enough for test but not the right one then get the right one and keep the test one as you may need it again.
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Do you know how important the program code would be for a test like this? I live in North Carolina but I brought the van out from California. The program code is JET0, which is apparently specific to CA (and NY?) vehicles. I assume that the CA cars have additional emissions parts, but I am not certain. Anyway, I imagine finding a local PCM with the JET0 code is not likely.
Thanks!
Dave
Thanks!
Dave
Fleet Owner
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From: Easton,Ks
There are no more emissions parts differences between the CA and the other states trucks other then you have a different Thermactor Pump and PCM Computer.
You could put the non CA Computer on it then you would have a non CA truck.
REFF:
Cal # CA truck:
http://i54.photobucket.com/albums/g9...cuum/Calif.jpg
Cal # Non CA truck:
http://i54.photobucket.com/albums/g9...Vacuum/Non.jpg
/
You could put the non CA Computer on it then you would have a non CA truck.
REFF:
Cal # CA truck:
http://i54.photobucket.com/albums/g9...cuum/Calif.jpg
Cal # Non CA truck:
http://i54.photobucket.com/albums/g9...Vacuum/Non.jpg
/
Mountain Pass
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From: St. Paul, MN
"I had some generic codes last time I checked, though I'll test again soon"
If you had some codes--read them and find out what they are.
If you had some codes--read them and find out what they are.
Last edited by rattosh51; May 5, 2009 at 11:36 AM. Reason: info
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That is great information subford! I have wondered what the difference was, and now the mystery is solved. This will also make it easier to find a new PCM.
rattosh51, I'll run out and pull codes as soon as the rain lets up.
Thanks!
Dave
rattosh51, I'll run out and pull codes as soon as the rain lets up.
Thanks!
Dave
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Ok, so the only code was 33, which is EGR valve not opening. I put a vacuum gauge and it made no change to the engine idle, so it looks like that could be it! I'll get a new one tomorrow and post what happens.
Thanks guys!
Dave
Thanks guys!
Dave
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Fleet Owner
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From: Easton,Ks
The vacuum line to the EGR valve does not have vacuum on it except when you are at about half throttle, at high way speed with a warm engine.
The EGR valve may be struck closed, the EVR (EGR) solenoid could be bad, the EVP sensor on top of the EGR valve may be bad or you could have a vacuum hose problem. ALL will give you the CM 33 code.
You need to get a hand vacuum pump and check the EGR valve first and at the same time test the EVP sensor on top of the valve with a meter.
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Yeah, it occurred to be this morning that I was not even testing the correct part... Looks like I need to dissect the EGR system and find out where the trouble is.
Results (or more questions) to follow
Thanks!
Dave
Results (or more questions) to follow
Thanks!
Dave
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Ok, I put a vacuum on the EGR at idle and the engine started to sputter, so it seems like the EGR is ok and the lines are not clogged.
I followed the green vacuum line from the EGR to what I assume is the EVR, though it does not look like either of the examples shown in my repair manual. Mine is shaped more like an upright cylinder, has two vacuum ports and one 2-pin electrical connection. The part number is FOTE-A1A 9J459. I tried blowing through the vacuum lines and it barely pushes through (book says no flow means it is good). It then says to apply 12v power and that it should open, though the jumper wire sparked when I tried to do this. Either I have the wrong part (and possibly just damaged it by juicing it up) or it is bad.
Any thoughts?
Dave
I followed the green vacuum line from the EGR to what I assume is the EVR, though it does not look like either of the examples shown in my repair manual. Mine is shaped more like an upright cylinder, has two vacuum ports and one 2-pin electrical connection. The part number is FOTE-A1A 9J459. I tried blowing through the vacuum lines and it barely pushes through (book says no flow means it is good). It then says to apply 12v power and that it should open, though the jumper wire sparked when I tried to do this. Either I have the wrong part (and possibly just damaged it by juicing it up) or it is bad.
Any thoughts?
Dave
Fleet Owner
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Posts: 23,667
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From: Easton,Ks
It sould look like this:
http://i54.photobucket.com/albums/g9...%20PCM/EVR.jpg
It sould have Red wire that is hot when the key is on (PCM Power Relay closed) and the other wire (BR/PK) is pulsed to ground by the PCM computer.
I think I read somewhere that you can not put 12 Volts on one pin and groung the other or you will burn it up.
The PCM only pulses it to ground./
http://i54.photobucket.com/albums/g9...%20PCM/EVR.jpg
It sould have Red wire that is hot when the key is on (PCM Power Relay closed) and the other wire (BR/PK) is pulsed to ground by the PCM computer.
I think I read somewhere that you can not put 12 Volts on one pin and groung the other or you will burn it up.
The PCM only pulses it to ground./
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Yes, that is the part. It certainly did not seem to like having the power and ground hooked up, and I now have a check engine light on today. I have not pulled the codes, though I am sure that I just added a dead EVR to the other continuing EGR system issue.
I'll pick up a new one and see where I get from there. I don't think there is much else that could be bad, besides the electrical sensor on the EGR and the PCM. I may have a good used PCM by tomorrow as well, so that will help narrow things down.
Thanks!
Dave
I'll pick up a new one and see where I get from there. I don't think there is much else that could be bad, besides the electrical sensor on the EGR and the PCM. I may have a good used PCM by tomorrow as well, so that will help narrow things down.
Thanks!
Dave
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I swapped the EVR and PCM with good used ones and it runs great! Unfortunately I swapped them at the same time, but I think the stumbling was due to the PCM. It not only pulls smoothly, but it shifts much better now as well. I guess there could have been a problem with the vacuum portion of the EVR, though it just does not seem like that would have made such a drastic difference.
Thanks again guys!
Dave
Thanks again guys!
Dave
