Interesting issue

[Shran]

Please excuse the story behind this but I feel it's necessary to give a good description of the problem I am having.

I went on a wheelin trip about two months ago. Truck did fine except a few instances where it would die if I hit a bump really hard or killed the motor when it was hot. It wouldn't start right back up, would just crank. I figured the TFI module was bad because if I let it sit for 10 minutes or so it would start again.

So I got home and replaced that. Seemed to be working fine until I went on another run a month later. I got to the trail, parked it for about 6 hours, and then drove it to the trailhead where I shut it off (100 feet.) Wouldn't start, engine was cold. Let it sit for a while and cranked on it, and it finally started. I figured it was the TFI acting up again, but figured I'd just finish the day and fix it later. Well I killed the motor at the top of a hill and it would NOT start. I let it sit for 45 minutes and got nothing, it would just crank but never fire. I had fuel pressure at the rail, good spark, the fuel pumps do prime, and the TFI module was just barely warm.

My last resort after checking the above was to pour fuel down the intake. It finally started after a bunch more cranking. I drove it out of the trail and have not had a problem since, but I am a little worried since this needs to be somewhat reliable on the trail.

It seems to me that since I have fuel pressure and spark that it could only be the injectors not firing, possibly because something got bumped loose. This seems likely since it only dies going up or down steep inclines or after a pretty good bump. Still wouldn't explain why it started after pouring gas down the intake. One would think it would run out of fuel and die.

Is there anything specifically that I should be checking for? I cleaned up all the grounds under the hood a few months ago, but will check them again. I think I also bounced a lot of water out of my battery the first time out...will need to check that too...could low battery voltage contribute to this?

And yes it had a full tank of gas, I did check that

 

[IMenriched]

any codes present?
might want to check the FPR too. make sure everything is dry under the cap and plug wires.

double check the interia switch reset it...if you bouncing on a trail it might of gotten tripped or is fualty

if you have fuel and spark then compression might be the missing link.

 

[Shran]

Haven't read codes (yet.) FPR appears good, no fuel in the vacuum line. I will get a pressure reading. Everything should have been dry...no rain at that time and hadn't gone through any water.

I also forgot to mention that the inertia switch was not tripped. I probably should just eliminate it anyway.

I also need to run a compression test on it, but I think that isn't the issue. It never burns any oil and it never has trouble starting except for these few times. There is fuel at the rail but it's like it's not getting past the injectors.

 

[armyets2003]

Just a quick suggestion, it seems relevent to me since my truck did me in a similar way, check your computer ground going to your negative battery terminal. Make sure its not just barely hangin on. Ug it still pi$$e$ me off when i think about that long a$$ night. Everything seemed to be working but no ground to the computer = no injectors firing.

Shawn

 

[Area 52]

I second that emotion...definitely electrical cutting out either on a ground or ignition circuit connection....check ALL grounds points including inspection of ground wires to terminals.

 

[Shran]

I finally had some time to look at this tonight. I have 30psi fuel pressure at the rail when it first pressurizes. With the motor running I have 30 at idle and around 40 when I crack the throttle. So everything's within specs there.

I inspected the computer ground on the negative terminal. It looks good. I have had that come loose before, but it's also the ground for the fuel pumps so it's fairly obvious when it's not attached. My fuel pumps were working when I had problems, so I think I can rule that ground out.

I also replaced the wire from the coil to the distributor cap tonight. The one that was on there had some very rusty ends so maybe that will help. I should probably just do plugs, wires, cap and rotor because I am sure they are 1986 originals but it runs so good as is...

 

[Frank The Tank]

I hope you figure it out man, my truck had a timing issue....... and she would be angry to start. But I'm sure from your description, something else is gnawing at your nerves.

Frank

 

[Shran]

Well I thought that after another new TFI module, I had things hammered out. Evidently not. I was driving it home from work yesterday and it started sputtering and would get worse if I got on the gas real hard. Typical TFI failure (again) I thought, so I warrantied my module and put in a new cap and rotor at the same time since they were also burnt up. It started right up after that and ran great for a couple minutes. I shut it off for the night, thinking it was fixed...

So this afternoon I get in it and it won't start again...****. Got spark, TFI is cool. I dumped more fuel down the intake and it started after cranking it a bunch. I let it run in my driveway and it sputtered and died after about 5 minutes. Still had spark so I'm ruling ignition out at this point.

Current symptoms:

High pressure pump runs until it overheats. I have erratic fuel pressure around 28-32psi and it jumps around more the longer it runs.

Tank pump is completely dead, as is the gas gauge. I think I have a wiring issue somewhere, maybe a ground? I have no idea! Grounding issue seems logical since both the tank pump and gauge have no power at the tank end.

Where are the grounds for this? Am I missing anything else?

 

[Area 52]

WAG: have you ever run low on fuel or out of fuel lately? I'm new to the BII's (old Bimmer dude) but if the intank pump has a fine screen on the 'shoe' pickup tube end, these could get plugged up with tank rust and varnish from the gas. This in turn will make the main high pressure pump work harder due to the reduced fuel flow from the intank pump's restricted pickup tube (screen). The main pump is cooled by the fuel flowing through it. The main pump may just be overheating (internal impeller expands) and jams against the housing around the impeller. No power to pump allows it to cool down; allows the internals to contract and free up. You go to start it and then after 5 minutes or so the cycle repeats. Does this make sense and do you think this could be the issue? The 'erratic pressure before stall out' symptom is also an indicator of this sitch. If you don't want to pull the intank pump to check it...you can always do a volume flow test. You should get about 1.8 liters in one minute out of the high pressure pump (use all safety precautions if you decide to do the flow test...eliminate sources of ignition...not in the garage...eye/hand/arm protection from fuel...etc.

 

[351rangerxxx]

i've had diesel engines with a weak signal from the pickup coil or speed sensor and they would not start without a little ether. so maybe you got a weak pick up coil in the dist.

 

[Shran]

I think I have it fixed. What a frickin ordeal...I blame Obama.

I began by cleaning up all the grounds under the hood which were all very corroded. Then eliminated the inertia switch, replaced some wiring to the tank pump that had been rubbed through and fixed (by me) before. That got the tank pump working again. Still wouldn't start though, so I assumed that since I have spark and good fuel pressure at the rail for sure now that it has to be the injectors not firing.

I did some wire tracing and found two under the dash that somehow got cut. I also found a cluster**** of speaker wire and dead ends that I guess were part of a radio at some point. Who ever did it hooked the ground and power wire for the radio up to the damn cigarette lighter. So after pulling most of the dash apart and fixing that mess and the two cut wires, it started right up. I think the injectors have like an initial start wire or something so that's why it would start and run fine when fuel was dumped down the intake. How it ever worked at all until now is beyond me but whatever, I think it's good now. I just finished cleaning up and I'm too tired to test drive it right now.