351 Efi motor stumbles and dies when good and warm

[74BroncoCO]

I have been chasing this issue for quite some time and I am beginning to get frustrated! The story is this...
Bronco was uber reliable in 2012 when I parked it and we moved overseas for 4 years. Every month or two, my dad would start it up and drive it around. Just before we got back stateside my dad once had the HP fuel pump fail on him (actually the leads shorted together), so I had him replace both the low pressure pump and high pressure pump. Then I had my cousin rebuild the motor and was hoping to have a trouble free experience. Prior to rebuild I had a Holley Red fuel pump and then the OEM bosch HP pump. (I still have both, but I think the red needs rebuilt at least given the noise it was making). We also put new fuel filters in as well.

The Low pressure pump is a Carter P4070. The high pressure was an Airtex E2000 and it would fail while driving around town. I first replaced the pressure regulator to no avail. Once the engine cooled off, it would go again until it had been at operating temp for a short while. I installed a pressure gauge on the fuel rail and noticed when it wasn't running well, my pressure would wildly fluctuate. So I replaced that pump with a Bosch, which is as close to the OEM pump as you can get (Motor is from a '95 F-250). I then installed a fuel pressure gauge in the engine bay after the LP pump. With the Carter/Bosch pump I was trouble free driving around town, to even include a 36 mile round trip on a hot day to pickup my son at school. I put close to 200 street miles on that setup with no issues. Though my issue was licked!

BUT this past weekend on the trail, it did the same thing. Drive around a while, doing trails and then it's starts to stumble and die. First time it failed, I got my 30 minutes on the trail. This time I got maybe two hours.

I do not run an accumulator and really trying hard NOT to. I want to keep everything as simple as possible and I know it ran well without one previously. I rebuilt the motor with as close to stock specs as I could so it's not like it's asking for more fuel.

I am still thinking it's fuel related; vapor lock specifically, but perhaps it's electrical.

But I am looking for things to try. I am tired of spending boat loads of money on fuel and camping to only get 2hrs of wheeling!

Thanks for any help!

 

[B RON CO]

Hi, did you check for spark when it died? EEC 4 TFI ignition modules ( screwed to the side of the distributor) are famous for hot condition failure, and come back to life when they cool down. Good luck

 

[74BroncoCO]

I did not check for spark. I have a remote TFI and it's not hot, or at least the first time it failed it wasn't. I didn't check it on this most recent failure.

 

[pcf_mark]

Did you see the same wild fuel fluctuations this time around?

My money is on the pre-pump (Holley Red). It is starving the Bosch pump and then the Bosch over heats. You can't pull fuel through the Holley pump so it acts like a restriction.

I would run the Bosch pump mounted low on the frame rail (safely) without the Holley and see how you do. I run only a frame mounted Airtex for four years using the stock non-EFI tank. Only issue I ever had is if I am low on gas (only one or two gallons left!) and I have a steep incline it can it can lose fuel pressure and run wonky.

I agree simpler is better an accumulator (in my opinion) is terrible idea.

 

[PaveBronco]

Wow same problem, down to the HP pump swap to a Bosch. I have an accumulator and bypassed with no change. Relocated my TFI, on a heatsink...and it gets hot, not sure if that's normal, and no change. My floor gets really hot so I figure its got to be vapor locking somehow, maybe my braided lines are keeping too much heat, unlike metal or the OEM nylon.
I gave up and ordered a Wild Horses EFI tank...

 

[Timmy390]

If no accumulator I see no need for the LP pump before the HP.

I'm running a E2000 mounted on the cross member at the stock tank. 3/8 Stainless lines (feed and return) with stock tank and no issues with heat thus far.

Tim

 

[Local Boy]

Sorry, I just re-read your post

Good Luck!

Aloha

 

[74BroncoCO]

Did you see the same wild fuel fluctuations this time around?

My money is on the pre-pump (Holley Red). It is starving the Bosch pump and then the Bosch over heats. You can't pull fuel through the Holley pump so it acts like a restriction.

I would run the Bosch pump mounted low on the frame rail (safely) without the Holley and see how you do. I run only a frame mounted Airtex for four years using the stock non-EFI tank. Only issue I ever had is if I am low on gas (only one or two gallons left!) and I have a steep incline it can it can lose fuel pressure and run wonky.

I agree simpler is better an accumulator (in my opinion) is terrible idea.

I wasn't able to catch it in the act. This time, once it died, it wouldn't run long enough to look. And since I had already wasted enough time with a broken rear yoke, I had my friends drag me to camp... That evening it started right up and got itself onto the trailer.

I had considered eliminating the LP and moving the HP near the tank so I am glad to hear you mention that! For the record, it was a Holley red before. Now a carter P4070.

 

[EFI Guy]

You really need to catch it when it's acting up and look at your pressure gauge, then check for spark. TFI is notorious for failing hot and starting up again after cool down. But the wildly fluctuating pressure gauge brings up another thing I would check...If you have an inertia switch (and you should), unplug it and examine the connector for it. I have seen a few that make poor contact, heat up, and start to melt the connector. It also causes the fuel pump to drop out intermittently.

 

[74BroncoCO]

I checked the inertia switch connector and it looks fine. No evidence of overheating.

I will have to get a fuel gauge routed into the cab. Was looking for a dual pressure gauge, but if I end up only running one pump, then I may not need that. Plus they are outrageously priced!

Do you have any faith in an electric pressure gauge? That seems like a more simple install and if I eliminate my LP pump, I'll have an open port right near the master cylinder.

 

[EFI Guy]

If you're going to have a pressure gauge in the cab, I would only do electric. You don't want pressurized fuel in the cab at all. They do make a mechanical "isolated" type but they are crazy expensive, or were last I checked.

My suggestion was to quickly check fuel pressure under the hood when it acts up.

 

[74BroncoCO]

I just spoke with my dad who was with me one time when it started throwing it's fit. He reminded me that we did check spark and it was there (Center post of dist.).

The biggest issue is that it seems very difficult to duplicate this behavior with my current setup. It seems to require a trail ride.

 

[sanndmann3]

What pressure regulator are you using? I had a stock regulator with 310 liter/hr pump and it would just quit after 20 minutes or more. rigged up a fuel pressure gage on the hood and watched it as it was failing. definitely pressure related. next we put a meter on the pump and watched current draw and voltage when it was failing and neither was a smoking gun. Friend of mine is an engineer at Ford who went thru similar issues. He recommended a more performance oriented pressure regulator and it seems to have fixed the problem... (fingers crossed)

 

[Nevadasmith]

I had a similar issue, but with a carb set up and mechanical pump, I know you have fi but my problem was the pick up in the tank rotted off, and when bouncing around on trails it would suck up crap and plug the pick up. Shut it off and wait a half hour, the crap all settled to the bottom, and I could drive 15mins-2 hours before it didn't again..... cleaned the tank and replaced the sending unit/pick up tube..... fixed my problem..... just one more thing to check! Good luck

 

[74BroncoCO]

My regulator is from O'reily's. Not my first choice, but I was limited at the time. Which one are you running?

I have given a little thought to junk in the tank. I'll pull that filter near the tank and see what it looks like.

 

[sanndmann3]

Aeromotive was the regulator I bought. Think it came from Summit...

 

[74BroncoCO]

Those Aeromotive regulators are quite expensive! Wow! I'm going to hold off on that for a while.

I pulled the rear most fuel filter to see if there was any junk in it. Fuel was clean, but I'd still like to someday replace that tank with one that suits my purposes better.

My plan is to move the HP fuel pump immediately in front of the tank and see how it runs then. I should verify that the fuel line that is in place will handle the higher pressures...

 

[74BroncoCO]

I have moved my HP pump to near the fuel tank and took it for a 3 mile cruise. Did just fine! However, the real test will be a trail ride as most recently, that is the only time it's given me issues. However, with the ambient temps getting considerably colder, I worry that I may have to wait until summer for a real test. But I'll gladly take a few trouble-free wheeling days between now and then..

 

[pcf_mark]

Great news! I bet as long as you have a quarter tank or more you never have any other problems.

 

[roundhouse]

I had a similar issue
Running the red Holley and a HP pump

Mine was overheating the fuel and causing it to boil
When it stalled out You could open the gas cap and stick your ear up to it and hear the gas boiling in the tank

I installed a power steering cooler in the return line above the back axle and that cured it

Then later the red Holley pump died and I had to bypass it to get home and I never replaced it
It runs fine with the HP pump as long as you don't run it empty

I installed the electric fuel pressure gauge and it was great , it quit working after a couple years though
https://www.summitracing.com/parts/...MI9qyhgYSb1wIVRSSGCh0LWABMEAkYAiABEgKtgfD_BwE