Car wont start or dies/Code reader error/Bad ground?

[jzbeaver]

In the last few days, my 1998 3.8 wouldn't start (or died) 3 times, but then did start again.

Here are some of the things that happened:

-each time, the battery cranked normally, and all lights worked
-all 3 times, I had driven at least 30 miles, so everything was warm.
-each time, when I plugged my code reader into the DLC, it had power,
but couldn't retrieve data-- i.e., an error message
-the 3rd time, it just died while driving, and I had to be towed back home

-each time, I got it to start again after doing something- (which may have nothing to do with the problem)
-the first time, after a short period just to tank up, I thought there might be a loose relay under the instrument panel, since the cover was loose, so I pushed up on the relays, and it started (but those relays aren't relevant)
-the second time, it had been sitting for several hours, and pushing up on the relays didn't do anything; but it had gotten much colder (from mid 60's to mid 40's, so I held a worklamp under the relays for 10 minutes or so
until they felt warm-- and it started.
-but then after driving about 35 miles, it just died. I didn't have a way of warming anything up-- and it had gotten much colder (low 40's)
-the CEL light had not come on, but I had disconnected the battery, so a pending code would not have been saved.

When back home, and able to do some research, including posts. I changed the PCM relay, and it started (but might have started anyway) and I have taken a number of short trips-- less than a mile or two, and it has been starting and running well. I am still reluctant to take it on a longer drive, as that's when the problems always happened, and I'm not convinced that the relay was the problem.

I have checked all relevant fuses (R and 20) -- they were all OK, and I cleaned the contacts. I was not able to do that before. The PCM relay contacts check out OK. The DCL grounds check out OK.

I suspect it might be a ground problem, involving the PCM only, or both the PCM and DCL. It couldn't be the fuel pump, because if it was, the DCL would still be OK and I would be getting codes or a PASS. But anything that
puts the PCM out of commission would also affect the DCL.

I have the Ford Electrical Vacuum and Troubleshooting Manual, and found several grounds that might be involved: 103, 105 , and 200

G105 ground, in the upper R engine compartment, is for the PCM relay, and the CMP and CKP sensor shields.

-I wasn't getting a good ground on this-- but the car started- so that is apossible culprit. I have now cleaned it. (At the same time, the CMP shieldwas not connected at the other end, so was not funtioning, and I couldn't
find any part of the CKP shield. But that has been the case for at least 2 years, when I had the alternator replaced, and I suspect the shop that did it just pulled them off to make the switch, and didn't restore them. )

G200 grounds one of the PCM functions and the fuel pump) It is at the rightside of the instrument panel, below the glove compartment. As it is not exposed to the elements, it looks and checks out OK.

G103 is the ground for some of the PCM contacts, the PCM relay, and the DLC. But I can't locate it! The Ford manual's location drawings are not very clear; it is supposed to be at the front of the transaxle, on the transaxle
stud (not sure where that is)nI don't have a lift, but put the front of the car up on tire ramps, and crawled underneath, and also removed the air cleaner housing, and I can't see anything resembling a ground connection. Since this is exposed to the elements, it is the most likely suspect, and I would like to be able to get at
it to check/clean it. (I can't locate G101 either, but it doesn't control any problem components)

I also wonder if the problem could be in the PCM module itself.

Some other factors that may or may not be related: For several weeks before these events, I have been getting codes for misfires on 2 cylinders (not usually at the same time), a bad oxygen sensor (once), and one for fuel/air
metering. I had just put a can of Chemtool B-12 in my tank to clean the injectors-- this has worked well in the past to get rid of codes. I also replaced the VSS about a year and a half ago. The engine has 203k on it.


Thanks for any help, esp. locating that ground.

jzbeaver

[jzbeaver]

Update: Problem solved/grounds located

In case anyone who reads or has read this post is interested, - I have
solved the problem:

It was cause by one of two things-- changing the PCM relay, and cleaning
the grounds for the PCM and DLC-- which may have been failing intermittently. Since I did both at the same time, I'mnot sure which did the trick-- but I didn't want to experiment and have to be towed again.

In my previous post, I hadn't been able to find the grounds, since the Ford manual places them on the top of the transmission. A tranny shop suggested
I look at the 2 ground wired next to the battery ground, and sure enough,
that's where they were-- and the Ford manual is simply incorrect!