Electrical issue

[mp470]

Hi all,

Took the truck out for a short drive yesterday, came back home to grab something to take it for a longer one. Shut it off, went inside, came back to start it, nothing. No accessories, lights as if there was no battery at all. Battery is brand new. Disconnected it for a while, starts up like a dream again. After a few starts and off cycles, turn the key, hear a click and then back to square one.  

Something else to note. Ever since I test drove it, it sometimes shuts off when pulling over to park - never at a red light though. It doesn't stall, just electrically shuts down but the oil and battery light remain on as in accessory mode.  

Now, while it's on and running, i jiggled wires around, positive to and from starter relay (also relatively new), negative (bit of exposed wiring near the terminal), computer wires. Couldn't recreate the issue. The battery terminals are pretty shot and i will be replacing them tomorrow.  It all really seems like an intermittently bad ground but I can't be sure. I haven't yet checked what the battery ground looks like at the other end (where does it go?).

Any suggestions would be appreciated.

Thanks,

Mike

[Gary Lewis]

Mike - I don't remember what engine you have, but it would help if you would put details about your truck in a signature so we do't have to try to remember.

Anyway, on most 8-cylinder engines the ground goes to the block and from there to the frame.  But, if you still have oil and battery lights when the engine stalls and don't have anything when you turn the key, it sounds like these are two different situations.  Yes?

Or, if it is an intermittent connection perhaps the engine dies and then the power comes back, illuminating those lights.

[85lebaront2]

Since you say computer wires, I assume you either have a feedback carburetor or one of the 5.0L EFI models. On the 5.0 and possibly the FBC engines the entire system grounds at the battery with a pigtail plug/socket assembly that looks very much like a power window motor connection. Since it is very close to the battery and is not a sealed weatherproof connection, it will corrode, giving a high resistance to ground which drives the electronics crazy. I would start there.

If you have the EFI engine, the 1985.5 and 1986 models are extremely sensitive to TPS (Throttle Position Sensor) voltage at closed throttle. These engines have a voltage specification for idle setting and there was a Ford IAC (Idle Air Control) bypass kit Ford had as a TSB (Technical Service Bulletin) solution. The issue arises that at a very small amount over 1.0 volts, I believe around 1.1 volts, the EGR (Exhaust Gas Recirculation valve)vacuum solenoid is activated. Since these early controls use a vacuum and vent solenoid pair to control the EGR, if the vacuum is activated, the RPM will drop, the EVP (Exhaust gas recirculation Valve Position sensor) tells the EEC "too much, vent", the feedback loop starts and the two solenoid valves near the battery start chattering like a squirrel.

[mp470]

Sorry guys, I set my signature but it's not displaying for some reason. It is indeed a 5.0 EFI. Thanks for the tips so far.

[mp470]

When it 'stalls' out while parking, it always starts right back up but when I turn the key and nothing happens at all, it's usually parked for a bit and stays like that until i unhook the battery for a while.  

[85lebaront2]

When you unhook the battery, are you taking off the negative cable? If so go back to my first reply on the ground for the entire EFI system. I think you will find the problem right there.

[mp470]

I hope you're right. I know what you mean, the small wire with the 1 pin connector on it spliced into the battery negative lug. I always unhook the negative first for a bit, but so far I've also been removing the positive, mostly to check the connection to the starter relay and clean up the lug itself.

[85lebaront2]

Suggestion, from my son's problems with his 86 F-150, bypass that connector by splicing (soldered) a long enough lead to allow a direct ground to the battery. A good body to battery ground while you are at it will help also. These trucks had a lot of ground issues which were corrected on later models.

[mp470]

Well i didn't end up bypassing the connector but re-did the battery terminals after cutting out enough of the negative cable where corrosion was evident. Hasn't stalled out since. I did however notice something else. The oil pressure light is still flashing when coming to a stop in gear. When in park / neutral, it doesn't flash. I just changed the oil with the proper amount and filter. Is the oil pressure sensor / switch capable of signalling the engine to shut off? The light flashes now but no stall.  Drives down the road perfectly at all speeds but the engine does seem to bog down some at idle after a few minutes. Almost seems like a misfire.

[85lebaront2]

No, low oil pressure will not shut it down, only one I know of is the 460 with hot fuel handling package. They have electric in-tank low pressure pumps controlled with a switch from the oil pressure fitting on the back of the engine.

On the low idle, possible misfire, can you hear the EGR relays chattering when it does this? I will have to find my idle set procedure for the 1985.5 and 1986 EFI systems.

[mp470]

Where are these relays located?  There is definitely a chattering coming from somewhere in that area.  I also tried unplugging the EGR while it was running, seemed to be more bogged down with it plugged in.

[85lebaront2]

They are located inside a plastic cover behind the battery, the "cover" is a vacuum reservoir. Here is a picture of a set of them:


The two on the right end are the EGR vacuum and vent, the black and red go to the reservoir.

[mp470]

Thanks for the photo, really appreciate the effort.  Time ran out tonight as it got dark but I did manage to pull the codes.  It appears to be a memory code 22 - MAP signal out of range.

[85lebaront2]

Ok, MAP sensor out of range could be a vacuum leak, or it could be going bad. It is a roughly rectangular black piece on the inner fender near the other EFI stuff and will have a larger hose attached and a three wire plug. Supposedly the 1985.5 and 1986 are by themselves, but I think I have successfully used a later one.

On the IAC bypass, the TSB is in the "Merry Christmas" thread (at least for now). Sometime I will try to find and scan the idle adjustment procedure for the 1986 MY EFI 5.0L, 1985.5 should be the same. I have acquired a number of the Ford diagnostic manuals (great big loose leaf books) and will get that to Gary for incorporation here.

[Gary Lewis]

Bill - The TSB's are easily accessed via the TSB link in the navigation menu, as shown below. No need to go to that thread. In fact, that's one of the beauties of this forum - the documentation is readily available.

And on the books, if you want to ship them to me I'll do the scanning and send them back. I have a service here in town that does a really good job for next to nothing.

[85lebaront2]

I might think about that, but they are pretty hefty.

[Gary Lewis]

Send them book rate.  Or UPS.  That's what Chris/Numberdummy say they may do on Bill's stuff.

I have lots to have her do, and will just put them in the mix.  And if you get them here before Sept 16th I can show them off at the get-together.

[mp470]

Any good way to test the MAP sensor without a frequency reading multimeter?

[85lebaront2]

No because the early computers will not deliver live data, I always kept a spare to try so I could see if it made a difference.

[mp470]

Well, scratch all that.  This was my first time pulling these OBDI codes and I was mistaken.  There are no codes at all (1-1).  I simulated a real 22 by pulling the plug on the MAP so I saw what that should look like.  Something interesting that I noted though...There is absolutely no vacuum on the hose going to the EGR valve.