Hey guys. Sorry for the long-winded post. I've got a 1988 Bronco and yes I am crossposting between the Bronco forum and here. Vinny (vjsimone) has been dealing with the brunt of my questions over there but he is the only one who is helping me out. I wanted to get help from you all here - especially since this forum is more active than the Big Bronco subforum.

The issue we have presently is that when I park the truck on an incline nose-up it won't start. The first time it happened we pushed it into the garage and put a tune up kit on it (flat surface) and it fired up fine - it needed new plugs anyway, I'm not a parts-thrower. I parked it in the same spot the other day and today it is doing the same thing. Cranks and kicks over but will not fire up. At first i figured it was a fuel drain back issue but with the amount of cranking and priming I've done, it ought to fire up just fine if it was purely a fuel issue. Between the first instance of this issue and today, it has started up and ran fine, though it has never been parked this way. Have tried to get fuel pressure after the first no start (back in November), but the tester kept registering 0 which was obviously not true since the truck did fire up and run after new plugs.

It has electrical gremlins running amok too - at each startup I do not have electrical power to the blower motor or the turn signals, and sometimes not to the power windows and wipers. Headlights always have power, as do hazards.

I have pulled the codes prior to this issue, both KOEO and KOER.

KOEO: Code 31, Continuous Memory codes: 32, 95.

KOER: Codes 41, 31, 77.

According to a couple trouble code sites I deduced the following: 31=EGR Valve Position/EGR Circuit below min. voltage, 32=EGR Voltage below Closed voltage, 95=Fuel Pump Circuit Open - PCM to motor ground, 41=System lean, 31=EGR Valve Position Circuit below min voltage 77=No goose test

I'm not sure if any of these codes have anything to do with the wiring issues on this old thing, I'm just not sure whether it is a combination of fuel and electrical issues which would cause the engine to not run.

I will be keeping this thread open just to get a second group of eyes on any issues I run across. Unfortunately, this issue occurred 2 days before I am set to go back to college so I won't have time to work on it much. Maybe we can brainstorm until I come home for break.... There's a whole host of issues we can go over, and once I have a plan it will be easy to grind out the work over the summer.

 

you are in good hands with vjsimone, but since you asked, i'll throw in my 2 cents ...

i would zero in on code 95 ... both your computer and your fuel pressure gauge are pointing to the same problem; fuel pump circuit . looks like a weak ground which can cause an intermittent problem. none of those other codes are going to cause a cranking no-start.

 

That's what I was thinking too. It's acting like its not getting enough fuel to fire up, yet it smells like raw gas after cranking on it for a bit. I've cleaned every ground I can see, nothing helped its still doing the same thing. Next step is gonna be pushing it into the garage where I can trace the entire fuel pump circuit not in the freezing cold.

 

Alright so Dad wants me to keep looking for solutions to the issue even though I'm away at college. On my last day home we found and cleaned all the grounds. By both headlights, by the firewall, the battery to motor ground, and the two ground straps from the frame to rad support. The only ground we neglected to clean is the one on the rear crossmember. Still no change. With key on the fuel pump primes correctly - no I have not managed to rent a fuel pressure tester.

 

Have you checked the PCM ground? If I remember right from one of Subford's posts the PCM is grounded from one of the pins. It is not a ground strap, rather it's a wire. Unfortunately I don't know which pin and where it is attached. However, based on the code definition it should be grounded to the engine.

 

i had one that had a bad pcm. sometimes it would power the fuel pump relay, other times it would not.
i ran a relay off a keyed power source through a oil pressure switch and a momentary contact push button switch.
turn key on, push button, and start truck. once oil pressure came up, let go of button.
this way if the engine shut off the low oil pressure would also kill the fuel pump to prevent leaks.
ran like that for 12 years.

 

Thanks Dday. Haven't touched the PCM ground, but now that you brought it up I'm sure I can find the pinout and trace the wire. Very helpful, more stuff to cross off the list!

That's an interesting one Tom, I don't know if that's our issue though. I can, at all times, hear the fuel pump prime for the required 2-ish seconds after the key is turned to "on". How much pressure it's pushing, I'm not sure. Does that sound like what happened to yours?

 

Keep the brainstorming coming guys - you're really helping out and giving me more ideas to look at when I get home.

 

The PCM ground is attached to the neg battery terminal. There will be one or two small wires coming off of the terminal that go to black quick-disconnects. It's a common failure point.

 

Technobabble - you might have just found a problem. I'll have dad confirm for me tomorrow - but I'm 90% certain there is only one wire coming off the negative battery terminal, which I traced to the engine block ground. No small black wires anywhere around there...... Oops, guess the computer would show bad grounds if there were NO grounds to be found.

 

The wires are pretty short (about 1ft), so if you look around a bit, you may find them if they corroded and just fell off the terminal. They enter the wiring harness right beside the radiator and AC condenser plumbing. It's also possible that the previous owner or shop may have cut these wires and terminated them on the frame somewhere. Especially if the neg terminal itself was ever replaced. Good luck.

 

agreed. even the diesel trucks with no computers had the small ground wire connected to each battery.

 

You guys are definitely inspiring me, love it! So it looks like the first thing we gotta do is track down those mystery ground wires that SHOULD be attached to the negative battery terminal. They pop out of the wiring harness by the radiator and AC condenser and will either be hanging ungrounded or attached to ground someway.

So, assuming we find the ground wires and fix them/reattach them and that doesn't fix the problem, what's the next move?

 

5 gallons of diesel and a road flare?
have you tried running separate power wire to the fuel pumps and try running it that way to eliminate a weak fuel pump?
when i was trying to diagnose the 04 with 5.4 gas engine, i ran a power wire to the output of the interrupter switch and let it run for a while .
well i tried to let it run, at 10 minutes it shut off like it was doing, which proved to me it was a bad fuel pump and not a relay or wiring issue.



my 88 diesel would drain back and not cold start the next morning when parked engine pointing uphill, which was the way i usually parked.
park on level ground and no problem. then one day i backed in to my parking spot to unload and left it there overnight. the next morning it fired rite up.
took me about a week of hard starts and another back in with it starting rite up and stayed running to realize i might have found the culprit.
i have a very small leak in the fuel return circuit. small enough that fuel would not leak out, but air would leak in overnight and let the fuel filter drain back to the tank when parked engine uphill. then when i tried to start it, the truck would fire on the ounce or so of fuel in the injector pump and lines, then run out of fuel and die. then i would have to crank the crap out of it to reprime the fuel system.

where i parked, when backed in the rear of the truck was about 6-8 inches higher than the front of the truck, making the fuel tank almost level with the injector pump. but pull in the tank would drop to almost 2 foot lower than the pump causing a siphon effect. and the very small leak in the return line was just enough to allow the fuel filter to drain overnight.

 

Ha! Thought about it more than once.... Bad news though. I was watching a video I took of the Bronco and saw that there are actually the two ground wires hooked up to the negative. That's what the start of classes and the return of collegiate alcoholism will do to your brain. Of course we're gonna check the wires out, but it might be time to move to step two...

Ok, so for this test could I unplug the fuel pump and run two wires to another 12v battery?

That's what I had initially thought, but the number of times I cycled the key to prime the system would have replenished any drained fuel. Additionally, we jumpered the fuel pump at the EEC test port to try and pull fuel pressure, and there were no signs of a fuel leak or smell of gas.