Engine Miss
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Engine Miss
Several months ago I was driving home from work and with out warning my truck bucked and started missing real badly. I was able to get home since I was very close. I found that the the miss was from the front 2 cyls on the passenger side. I had no change when I unplugged the ucvh for these cyls. I checked and the other 3 plugs and it severely made a difference. I have replaced the harnesses and valve cover gaskets and still have the same issue. It seems to put out some white smoke and gets heavier as you rev it up. I see a lot of good info on this site and could use any input. I was wondering if the injector control module could cause this. I took it out and opened it up,it is clean and dry and no funny smells also.
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I used factory parts so what I replaced was the valve cover gaskets and the harnesses that connect under them to the injectors and glow plugs. They didn't look or smell burnt at all. One more thing. about a month before this problem the fuel pump starting leaking badly out the weephole so I replaced that with a new factory one also. It ran great up until the minute it started missing. A friend of mine said his powerstroke developed a miss and he replaced all the injectors himself and it didn't fix it so he had it towed and they replaced a sensor? I cant see how a sensor would cause just 2 cylinders to fail, especially being the 2 share the same connector on the valve cover.
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From: Orrville, Ohio
I think if it were me, I would ohm out those connectors to the injectors. The easiest way to do so would be to unhook the connector at the IDM and ohm all the way through the wiring to the injectors. That will eliminate all the wiring in between in one fell swoop. I am kind of wondering if you don't have an open wire somewhere in the common for those two injectors (they share a common - ground - wire).
Here is the pinout at the IDM:
The two front cylinders on the passenger side are cylinders 1 and 3 so you're going to test between pins 6 and 24 and then pins 21 and 24.
Here is the pinout at the IDM:
The two front cylinders on the passenger side are cylinders 1 and 3 so you're going to test between pins 6 and 24 and then pins 21 and 24.
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DIYmechanic, Thanks for the diagram, I wish I checked in sooner. I just ran through as much test with my fluke as I could and really couldn't determine anything except I do not believe have any open circuit or shorts to ground on the injector circiuts. I borrowed a scanner today and came up with p1271,p1272. but that I found is very vague. I will get at it again tomorrow using the diagram you posted. I believe I might be the ground after what you told me. The Injectors seem to have similar readings on the known good ones compared to the suspect ones but I guess they could be stuck mechanically. I had the valve cover off and the idm disconnected checking the wiring and its all back together now. Do you know where the actual ground is?m Pin 24 controls 1357 so I would think I would have the entire bank down if that was bad. Thanks again for taking the time to shoot me the info, I will take as much as you have on this. I haven't had much problems so I am learning as I go. 
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Joined: Dec 2010
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From: Orrville, Ohio
The trouble codes you have are as follows:
* P1271 High to Low Side Open - Cylinder 1
* P1272 High to Low Side Open - Cylinder 2
That tells me that you're on the right track looking at the wiring. I think the next step should be to ohm out the injector wiring all the way from the injector to the IDM. You are correct that the common (Pin 24) serves all the odd numbered cylinders, but the wire splits at some point in the harness to go to the two individual connectors on the valve covers. I guess if 1 and 3 aren't firing and 5 and 7 are, I would start looking for your issue where the split is made. Really though the first step is to ohm it out and make sure that you really do have an issue with that wiring. If there is an issue with the IDM or even the PCM this could be a phantom code all together. Logic says that's not the case but it's best to confirm that with the 'ol Fluke anyway.
I should clarify that this is not really a "ground" for those injectors either, it is more of a common that serves that side of the engine. I do believe it is the return path for the injectors, but I don't think it should ohm out to the chassis on the truck. I can't confirm that, but I think that is the case.
* P1271 High to Low Side Open - Cylinder 1
* P1272 High to Low Side Open - Cylinder 2
That tells me that you're on the right track looking at the wiring. I think the next step should be to ohm out the injector wiring all the way from the injector to the IDM. You are correct that the common (Pin 24) serves all the odd numbered cylinders, but the wire splits at some point in the harness to go to the two individual connectors on the valve covers. I guess if 1 and 3 aren't firing and 5 and 7 are, I would start looking for your issue where the split is made. Really though the first step is to ohm it out and make sure that you really do have an issue with that wiring. If there is an issue with the IDM or even the PCM this could be a phantom code all together. Logic says that's not the case but it's best to confirm that with the 'ol Fluke anyway.
I should clarify that this is not really a "ground" for those injectors either, it is more of a common that serves that side of the engine. I do believe it is the return path for the injectors, but I don't think it should ohm out to the chassis on the truck. I can't confirm that, but I think that is the case.
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I wasn't able to get to look tonight, after reading your last reply I am thinking it might be a wiring issue at the weld point for the ground. I put a fuel pump in about a month before this happened and had that harness was moved out of the way for the first time since 1997. I know harnesses and wiring can get brittle over the years so I will do a little investigating tomorrow and let you know what I find. It seems to be running rich, blowing out smoke like when first started on a cold winters day after forgetting to plug in the block heater. So that concerns me that is not an open circuit. That should shut the injectors down and cause a lean condition. I just cant think 2 injectors would go bad at the same time either. It ran fine up to when it started the miss and it is missing 100% of the time now. SO maybe defalt mode of these injectors is to stay open. Still plugging along and not ready to tow to the pro's yet!!!
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Post Fiend
Joined: Dec 2010
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From: Orrville, Ohio
I wasn't able to get to look tonight, after reading your last reply I am thinking it might be a wiring issue at the weld point for the ground. I put a fuel pump in about a month before this happened and had that harness was moved out of the way for the first time since 1997. I know harnesses and wiring can get brittle over the years so I will do a little investigating tomorrow and let you know what I find. It seems to be running rich, blowing out smoke like when first started on a cold winters day after forgetting to plug in the block heater. So that concerns me that is not an open circuit. That should shut the injectors down and cause a lean condition. I just cant think 2 injectors would go bad at the same time either. It ran fine up to when it started the miss and it is missing 100% of the time now. SO maybe defalt mode of these injectors is to stay open. Still plugging along and not ready to tow to the pro's yet!!!
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Sorry I haven't responded sooner, I have been so busy plus I had the flu for a few days. I am working on testing the wiring harness today. In reference to your picture. All the connectors are secure. I had replaced the harnesses under the valve covers and then recently replaced the valve cover gaskets also. The 2 cyls on that connector you posted a pic of are not firing at all. There is no change in engine idle when you unplug it. I am hoping to find a broken wire. If no,t I am at a complete loss for what to do next besides tow it to the dealer and I don't have enough zero's in my checking account for that!!
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I just ohm'd outt he wiring and there is no breaks, I checked for short to ground also. I also tested from pin 24 to pins 6,21,8,20 through injectors and had 3.0-3.3 ohm's on all. I believe I read somewhere that this is normal. Could an IDM cause this? Im lost???
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I did, Early on before I replaced any parts. It was dry and had no burnt smells. The harnesses and valve cover gaskets didn't look burnt of smell burnt either. That is what is making this so difficult. Those 2 clys failing at the same time to me would rule out the injectors, so I cant come to any other conclusion but the IDM? If I knew of someone with a similar truck I would swap it out as a test.