How do you know if PCM is bad?
01-29-2011, 05:05 PM
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How do you know if PCM is bad?
I'm still working on my non-running '87 F-150 with a 4.9L I-6. When checking for trouble codes I get a message on my scan tool saying "connect scanner to DLC". The problem is that it is connected. The battery is fully charged. The symptoms of the truck is that it is very hard to start and to keep it running you have to constantly (every second or so) press the gas pedal just to get it to act like it is running on 4 or 5 cylinders. Of course it has no power.
This is a project that had so many potential problems it was hard to know were to start:
1. prev owner tried to start it on 2-3 year old gas (and very little of it)
2. hadn't ran in 2 years
3. had oem plugs and wires after 24 years and 125K miles
4. last documented oil change in June 2004
5. has about 4 amp steady current drain with no obvious source
Things done to date:
New HP fuel pump (prev owner had this done)
new fuel filter
replaced injectors with later model rebuilds
new FP reg
new plugs, wires, cap, and rotor
new vacuum lines
added fresh fuel (shell premium) and Seafoam
Results:
Still runs the same (terrible)
fuel pressure is good 40-50 PSI
Any ideas before I by a rebuilt PCM and try it? I am guessing that the PCM, if damaged, could be the source of the 4 amp current drain which will discharge the battery in ~1 week. I've never had my scan tool not recognize it was plugged into the DLC.
This is a project that had so many potential problems it was hard to know were to start:
1. prev owner tried to start it on 2-3 year old gas (and very little of it)
2. hadn't ran in 2 years
3. had oem plugs and wires after 24 years and 125K miles
4. last documented oil change in June 2004
5. has about 4 amp steady current drain with no obvious source
Things done to date:
New HP fuel pump (prev owner had this done)
new fuel filter
replaced injectors with later model rebuilds
new FP reg
new plugs, wires, cap, and rotor
new vacuum lines
added fresh fuel (shell premium) and Seafoam
Results:
Still runs the same (terrible)
fuel pressure is good 40-50 PSI
Any ideas before I by a rebuilt PCM and try it? I am guessing that the PCM, if damaged, could be the source of the 4 amp current drain which will discharge the battery in ~1 week. I've never had my scan tool not recognize it was plugged into the DLC.
01-29-2011, 05:40 PM
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holy crap batman 
!! You've had your work cut out for ya!
you can pull the PCM and separate it to look for burn marks on the boards...that should help. also check the wires for the plug for burn marks/tears/crimps/gashing. Clean the DLC contacts, and check the wires that lead to the harness for dry wire insulation.
good luck, hit us back with your results
!! You've had your work cut out for ya! you can pull the PCM and separate it to look for burn marks on the boards...that should help. also check the wires for the plug for burn marks/tears/crimps/gashing. Clean the DLC contacts, and check the wires that lead to the harness for dry wire insulation.
good luck, hit us back with your results
02-01-2011, 10:52 AM
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Here's an update on my truck:
The running problem was that I had the #2 and #4 plug wires switched at the distributor. Once I got that straightened out the truck purrs like a kitten and has good power. I fixed a multitude of problems to get to this point.
The ~4A current draw ended up being a bad diode in the alternator. A rebuilt alternator cured that issue. So now I have a truck that runs well and the battery doesn't discharge every week.
I still have a couple of minor issues:
1. the temp gauge doesn't work (sending unit?)
2. the fuel level gauge doesn't work (will use trip meter)
The only thing that still bugs me is that I never made a confirmed connection to the ECM with either my scan tool nor using the jumper wire and flash method. Is it normal for this year/model to not read anything from the ECM if there are no fault codes present?
The truck runs too good for there to be an ECM issue.
The truck is rust free with a straight body and fair interior (needs seat cover). The tires are like new and the battery is just 2 years old. So far I'm into it for $1550 including the purchase price. It had only been driven ~1500 miles since 2004 by the previous owner, my brother-in-law.
Tomorrow its going to the inspection station and then to the tag office for plates and registration. It will be road ready just in time for the next snow
The running problem was that I had the #2 and #4 plug wires switched at the distributor. Once I got that straightened out the truck purrs like a kitten and has good power. I fixed a multitude of problems to get to this point.
The ~4A current draw ended up being a bad diode in the alternator. A rebuilt alternator cured that issue. So now I have a truck that runs well and the battery doesn't discharge every week.
I still have a couple of minor issues:
1. the temp gauge doesn't work (sending unit?)
2. the fuel level gauge doesn't work (will use trip meter)
The only thing that still bugs me is that I never made a confirmed connection to the ECM with either my scan tool nor using the jumper wire and flash method. Is it normal for this year/model to not read anything from the ECM if there are no fault codes present?
The truck runs too good for there to be an ECM issue.
The truck is rust free with a straight body and fair interior (needs seat cover). The tires are like new and the battery is just 2 years old. So far I'm into it for $1550 including the purchase price. It had only been driven ~1500 miles since 2004 by the previous owner, my brother-in-law.
Tomorrow its going to the inspection station and then to the tag office for plates and registration. It will be road ready just in time for the next snow
02-01-2011, 10:59 AM
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Hope you addressed the 7 year old oil or plan to before you get that thing on the road. If you haven't already, might want to do the seafoam procedure on the crankcase to work out some of the sludge that's surely in there.
02-01-2011, 12:49 PM
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Yep, new oil and filter have been done. Surprisingly everything was very clean. All the same, I plan on changing the oil again in about a week to flush out anything that may break loose and then again after about 1000 miles. I plan a complete fluid (trans, t-case, diff, coolant, and brake) change over the next couple of weekends.
I removed the valve cover and replaced the gasket to fix an obvious oil leak. There was no sludge build up on the head casting whatsoever. It's a good thing that the truck was basically parked in 2005 and has only recently (2009 and 2010) attempted to be resurrected, each time on the old fuel that was in the tank when parked. I warned my brother-in-law not to even attempt to start it on the old gas but some people just don't listen.
His loss is my gain. I think the truck could easily bring $2500 now but we needed another 4x4 in the family with all the snow we've been getting in western NC.
I removed the valve cover and replaced the gasket to fix an obvious oil leak. There was no sludge build up on the head casting whatsoever. It's a good thing that the truck was basically parked in 2005 and has only recently (2009 and 2010) attempted to be resurrected, each time on the old fuel that was in the tank when parked. I warned my brother-in-law not to even attempt to start it on the old gas but some people just don't listen.
His loss is my gain. I think the truck could easily bring $2500 now but we needed another 4x4 in the family with all the snow we've been getting in western NC.
02-01-2011, 12:53 PM
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oh really? where in western nc are you? I have family in asheville (brevard, actually, but it's easier to say asheville) and I regularly do the drive from asheville to pigeon forge, tn
02-02-2011, 08:07 PM
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Canton, NC which is about 11 miles west of Asheville. I travel a lot to Pigeon Forge and the surrounding area. I have a '64 Buick that we take on long drives on the Blue Ridge Parkway and through the Smokies. It's a small world. I grew up and lived in Mansfield, Ohio until I was 39. I've been down here for about 6 years now.