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seedpress

Fuel Delivery Problem

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I just ran a little test on my fuel gauge system, and now -- even though my fuel pump runs strongly -- the truck won't start. The fuel pump runs (continually) but the engine is not firing. I've got a '90 Bronco with the 5.8 liter.

 

Here's what I did:

 

I pulled apart the C441 connector at the tank to see if I could electrically test my sending resistor. When I started the job, I may have mistakenly put my meter's ohm tester in the connector that goes back to the engine area, instead of testing the wires that go into the tank. The electrical diagram shows that the wires from the fuel pump are connected to the inertia switch, the fuel pump relay, and the EEC (Electronic Engine Control Module). It's possible that I sent + or - 9 volts back to the EEC. Anyway, after I ran the tests with my meter, the engine wouldn't start, despite a strong sound from the fuel pump.

 

Could the ohmmeter connection back to the front of the engine have damaged the EEC, or something else, and now be the cause of the failure-to-start? I'm now stranded!

Edited by seedpress

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Last night I took the battery cable off and left it overnight. Then today, in the process of trying to run the error codes, I turned on the truck and the pump primed correctly and the engine started. I had tried leaving the battery disconnected for an hour or so before, and that didn't help.

 

The only thing I can figure out is that maybe when I hooked up the tester, the electrolytic capacitors in the computer module got reverse polarized and punctured the dielectric, leading to a malfunction and maybe also a computer glitch of some kind. Then, after leaving things with no power long enough, the computer reset and/or the capacitors had time to self-heal. Electrolytics will do that.

 

Anyway, I'm left uneasy now because I don't know for sure what is happening. It's all partially-informed speculation.

 

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yo,

It may have not damaged anything since it did start; but your Cap idea sounds interesting!

EDIT:

and from memory, if the engine was off @ that time and ign sw is off, then that 9v just travelled back to the load side of the FP relay; since the FP relay was not "closed"? But as you wrote; that ckt also routes via a splice & then thru the inertia switch to the EEC?

Burnt PCM pic in a 94; "...the capacitors inside burned and leaked on the board. it happened to all of them, one was worse then the others..." see Mike's pic here; http://img.photobucket.com/albums/v312/kermit0069/ECM002.jpg

 

 

Can you check for Codes; such as this way by our pal BroncoJoe?

SELF TEST - COMPREHENSIVE & Connector Location pics, Bronco & Ford; "...The self-test plugs were mounted on the passenger side fender on 1985-86 EFI trucks; The self-test plugs are located along the driver's side fender behind the air filter box on 87-95 EFI trucks..."; miesk5 NOTE; Self-Test Output (STO) is the Pin in the Lt gray Connector and Signal Return Ground (SIGRET) is Pin E in black Connector in 87-95; The engine temperature must be greater than 50°F (10°C) to pass the KOEO Self-Test and greater than 180°F (82°C) to pass the KOER Self-Test. Run it around to heat the engine up and shift thru all gears incl Reverse. Then turn off all accesories/lights, etc. Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch. Do Key On Engine Off (KOEO) portion first. Look Codes up in my broncolinks.com site using the new Search function.

Source: by BroncoJoe19 (Joe) at Ford Bronco Zone Forums

 

http://broncozone.com/topic/14269-code-reader/

 

Post any results here.

 

GL!

Edited by miesk5

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I've arrived at a temporary solution:

 

After testing the "run" system, it turned out that the relay itself was not sticking. The problem was the EEC itself, which was was signaling the pump to run continuously. This was an intermittent problem, so it was difficult to pin down for a while.

 

I finally pulled the computer and, sure enough, two of the electrolytic capacitors had leaked. Not only were they shot, but the leaked electrolyte had begun corroding some pins on one of the semiconductors. The computer board is covered with a conformal coating to protect it against moisture and contamination, but the electrolyte had also seeped under or through that coating and discolored the board in places.

 

First I cut out all three of the electrolytic capacitors, although only two of the three had leaked. Then I tried to clean the spilled electrolyte. To remove the corrosive electrolyte I had to strip off the conformal coating where I saw board discoloration. I tried to clean the affected areas with rubbing alcohol, dilute acetone (used for finger nail polish remover), and WD-40. Also, one logic IC (integrated circuit) had three pins that were corroded by the electrolyte. I tried as best as I could to clean them mechanically.

 

The two leaking capacitors were 47uF 16V, and the third a 10uF 63 volt. I didn't have these values on hand, but coincidentally I had just bought a hundred 22uFs with a 63V working voltage. So by paralleling two of the 22s I was able to get 44uFs, and in series I got an 11 uf. Electrolytic caps have a wide tolerance range anyway, so I hoped that would be good enough. The one problem was all the original caps were 105 C temperature, whereas my replacements are only 85 C. But my computer is behind the driver's kick panel, instead of in the engine compartment. So, I am hoping it will work, at least for a while.

 

It was a pain to replace the caps! First, I found it difficult to solder the new, "paralleled" capacitors to the printed circuit board. Then, I wasn't sure how many layers the board had -- it's easy to overheat and ruin underlying layers. Finally, some of the copper pads to which the new caps were being soldered were also very close to fine-pitched copper traces. My finished "repair" is a real mess! But it seems to be working.

 

After all this, the pump is no longer latching up in the run position, and the engine starts. The Bronco hasn't been driven on the road yet. So, I guess I'll see how that goes soon. I am planning to get a replacement computer pretty soon, because I don't trust the old one, especially with my "iffy" repairs.

 

I'm not proud of my fix-it project, therefore I'll leave the finished product to your imagination; however, if you ever look inside your own EEC, you might want to know what leaking caps look like, so here's the “before” picture of my leaking caps:

 

IMG_4531-mod4.jpg

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yo!

 

Good stuff!

 

I know of only one other person that has replaced the CAPs in an EECiv

Failures Due to Age; "...The patient in question is a remanufactured A9L unit. This ECM is the one from a little notch project I'm working on. It started giving some problems starting up, engine flooding, random hesitation, missing and stalls. I opened up the ECM (the car is running with a A9S unit) after the owner brought it for a checkup.What you see is the typical electrolytic capacitors leak, causing intermittent shorts/opens to the neighboring circuits/components and symptoms as the ones explained. Worst case scenarios with this type of failure, is a permanent no start and permanent damage to the PWB preventing it could be repaired. As soon as I replace the capacitors I'll update with the pictures showing the repairs. The following capacitor does not show any leakage problems however, it will also be replaced as a preventative measure..." read more

Source: by Joel5.0 at http://sbftech.com/index.php/topic,15654.0.html

 

I'll add this Link to my site, ok?

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yo!

 

 

I'll add this Link to my site, ok?

 

Go ahead and add the link if you want. As long as it's okay with this board operator, it's fine by me.

 

yo!

 

Good stuff!

 

I know of only one other person that has replaced the CAPs in an EECiv

 

I'll add this Link to my site, ok?

I think you'll find more of these caps failing as time goes by. It's the most vulnerable component. Most people who rebuild old electronics have to replace the electrolytics as a routine matter.

 

By the way, the link went to a forum, but not to the actual post.

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