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1991 240 Fuel Pump Mystery

MrBill said:
I thought he just wanted you to put a clip on the terminals the fuse fits between.
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I feel than an alligator clip across the terminals would be vulnerable, plus the terminals are scorched so not sure I could appropriate voltage flow vs. just pulling the wires out of the back of the fuse panel and jumpering them.

I dunno...maybe I'm over thinking it.
 
He was saying to just temporarily jumper it as a diagnostic step, not to drive around like that for the next decade.
 
petebee said:
I feel than an alligator clip across the terminals would be vulnerable, plus the terminals are scorched so not sure I could appropriate voltage flow vs. just pulling the wires out of the back of the fuse panel and jumpering them.

I dunno...maybe I'm over thinking it.
Click to expand...

Vulnerable? The alligator clips are just for a test. If you kick it loose during your test drive, you will stall the car. If this is possible, don't drive it anywhere that way.

You said the fuse terminals were scorched and a little warm. If they are visibly scorched, they got more than a little warm - they got very hot.

On the other hand, you said the fuel injection relay was warm. It is warm normally. The coil in each of the two relays dissipates enough heat to raise the temp of the relay box above comfortable handling.

As for making the in-line fuse repair, your plan sounds OK to me, although I might build it a bit differently depending on what I find in there. There are spare tabs on that fuseholder, and #6 has a common supply with other fuses, so I might just plug that pigtail assembly on the spare tabs instead of butchering the harness. Depends on what it looks like, and whether the harness could stand a little trimming. For you, it might depend on what tools, materials, and skills you have.

Tell you what: We have two 91's both over 300K and they are daily drivers for my daughters. Both cars have exhibited this fuse 6 syndrome in the past. My most recent fix was short of what I recommended -- I just cleaned the fuse panel, retensioned the terminals, and used copper (similar metal) fuses.

My kids are familiar with the good advice JohnMc offers 240 owners about rolling fuses. My assumption is all 240 owners have learned this over the years. But of late, since the replacement with copper fuses, they haven't mentioned needing to tweak that #6 in the morning to get things going.

Next opportunity, I will take my own advice about the bypass pigtail, photograph its installation, and post it in this thread. Stay tuned and you'll have the step-by-step, but meanwhile you'll have to listen to your own sensibilities. :-D
 
Didn't think about a blank tab in the panel...it actually has an open spot. I'll just transfer the fuel pump wiring over to that one (if it can reach).

Then we can drive around for the next decade :-P
 
luchy72v said:
On wednesday I might attempt to drive all the way to work (35 highway miles) and see how it goes.
Click to expand...

DAY ONE: 70 miles round-trip today, without a stall. I am not getting excited about only one day's results but have a couple more days commuting before weekend wrenching-time.

Looking forward to the bypass pigtail documentation; this or the "blank tab redirect" sound like great options to me....
 
Well I did the bypass jumper for fuse 6 (including a 15 amp blade style in line fuse) and car will run but is still stalling occasionally in reverse - especially with a quick stab of throttle.

I checked the ECU and it is the 951 version.

Seems like it is worse once car is warmed up and restarted within a few minutes. I can hear it starving for fuel (extended cranking before it fires), then it goes into low speed stall mode. Keep throttle up and it won't stall, only during slow speed maneuvers (turns, reverse, etc.).

Dying fuel pump maybe?
 
I eventually found a poor connection at the fuse box. After pulling it out I discovered a loose cobbled-together jumper cable linking the #4 fuse (fuel pump) and the #3 fuse (heater fan). A yel/red wire that should have occupied the jumpered lug was just hanging loose.

I tightened & resecured the jumper cable and now the car is running as it should without stalling. However I can't help but wonder why someone did this in the first place and what it's a workaround for?
 
to clarify: I tightened up the as-is workaround jumper (and put some electrical tape over the end of the hanging yel/red wire). I would love to hear if anyone has any ideas why this workaround might have been put there in the first place...or if I should try to restore the original wiring configuration....
 
Without looking at a wiring diagram, it sounds like they jumpered the fuel pump to a switched 12V power source, thus bypassing the fuel pump relay and the ECU that needs to trigger it. The early failure prone ECU's often failed to trigger the fuel pump relay properly (among other things, I think).

The only real danger with this is in case of a crash, the fuel lines could split, and the key could remain on, and it could pump fuel into a possible fire. The ECU kills the fuel pump if it senses the engine isn't running any more.

So it's probably a work-around for either a fuel pump relay or flaky ECU.
 
my 1985 is doing this very thing. I can jump the relay however, and it still will not run even though I hear the pump kicking in. could this be due to having that stupid fuse behind the battery?
 
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