Hesitation / no power when engine compartment is hot (1 Viewer)

[jpoole]

If the new pump / parts don't solve the problem and fuel pressure remains low be sure to check the voltage to the pump and ground(s) for the pump. Hopefully the new parts will have you rolling at full strength but if not the pump may not be seeing proper voltage or have sufficient ground in some scenarios/etc..

My friend with his '94 that was low on power found a number of issues in this area that had plagued his 80's performance in different conditions for years and in spite of parts replacement. I think that running tests (some while driving) with a multimeter connected in different ways/at different points along with adding bypass grounds and leads that could be switched on/off during operation helped him understand the systems involved and isolate where the problems were, etc. I wasn't on-site but I seem to recall that one issue was a wiring connection/junction inside the fuel tank that caused voltage/ground drop between the connection on the top of the tank and the pump itself.

Your logic seems sound overall and a rust free 80 means you'll get years of driving once it's sorted. The tests outlined in posts above and in my previous paragraph may feel like the long road but we all want to help you get past this troubleshooting phase and to the point where you can drive it as soon as possible and in our experience testing and understanding what the problem(s) actually are is the quickest/surest way to get past the issues. If you have a multimeter and know how it works many of these tests are quick to perform.

Thanks for the responses and keep us posted!

 

[NelsonCruiser]

Have the same problem with my 94. It’s Fine if I leave the hood open after I drive it to let it cool down. Looking forward to finding a fix with this thread!

 

[OrangeCrusher]

All parts arrived today - earlier than expected. Wrenching time!

So here is what I found:

That's literally how I pulled it out of the tank! Unbelievable it ran at all and produced a somewhat consistent pressure. I drove it for 700 miles like this...

The pump otherwise looked fine. It is the same model that I had ordered as well - Delphi FE0402. I decided to replace the pump with the new one regardless, and keep the old one as a spare. I also replaced the rubber hose, the hose clamps, as well as replaced the zip tie that mounted the old pump to the bracket with a clamp. No idea how that is supposed to be done? But the clamp looked like a solid solution.
This is how it looked like when I put it back together:

I then tested the new and the old FPR with compressed air. In direct comparison it is extremely obvious that the old one is bad - it does not open (properly).

So I assume the chain of events here was: FPR failed -> high pressure -> hose blew off the pump. Probably happened before I bought the rig as it never ran right, but who knows.

Once I put it back together, I immediately noticed that it starts much better now. It used to take a few seconds to catch. Now it's nearly instant. I assume that's because there was always some vapor in the rail that had to be pushed out before it could start.

It then ran poorly - for the reason we already suspected and discussed above: The VAF was now out of adjustment. I had to turn the clockspring mechanism about half a turn in to bring it again into what seemed like about the right set up.

After that, it ran great! Also for the first time, throttle response out of idle was great. It always had some hesitation there before - I assume it was because of the loose VAF spring adjustment that made the VAF be sluggish / stuck.

However some "new" problems emerged then that kept me busy until very late in the evening - fuel was leaking out of the #2 injector / rail connection. Must have been my mistake when I replaced the injectors. So I had the great pleasure of taking the whole intake manifold thing apart again It turned out that the o-ring for that injector was damaged. I must have put it in crooked... Luckily I had another injector service set to fix it.

Once that was done, it leaked at the fuel filter. Not sure if that was already the case before and I didn't notice it, or whether I didn't put it together properly. In either case I had a new fuel filter already lying around, so decided to take it as an occasion to replace that one.

I then let it idle for about 20min, and it seems to be all good now. I can't drive it right now because I have parts of the transfer case taken apart - the whole CDL setup is not working (actuator doesn't work - looks like the board that mounts the motor brushes is broken, and all the switches/connectors are broken).

I should have everything back together on Friday and hopefully can drive it on the weekend to confirm this is actually fixed - but I'm very optimistic!

Thanks @Malleus for all your responses - your comment that the fuel rail should be cold when the engine is running, really made it click!

 

[Malleus]

I'm glad you solved your engine problems.

That's a new one, for sure. Maybe you have fuel tank gremlins.

I had the same injector problem when I refreshed the head on my son's 80. I nicked an O-ring on one of the injectors and it leaked like a sieve. You really have to grease them well with gasoline and twist them in to keep that from happening.

Those crush washers on the fuel filter are a PITA. Substituting them with the bent washers was one of Toyota's better ideas (the power steering pump fitting and brake lines to the calipers are the same way). I'll never use those single washers again, unless I absolutely have to.
I don't think anyone mentioned it in your thread before, but slotting the rear hole in the fuel filter bracket makes getting it out, and in, much easier.

 

[OrangeCrusher]

I think I found some gremlins now in the fuel system, but not in the tank - instead in the wiring harness! @jpoole I think your instincts were, right in the end!

The positive power to the fuel pump ran through this professionally prepared wiring junction.

This professionally prepared wiring showed a very low resistance, as can be seen by the low losses and corresponding low temperature in the IR camera image.

Sarcasm off. I have no idea who prepared this - someone wired in something in there at some point. I found four of such horribly prepared connections in the the wire to the fuel pump. Another one below.

This didn't cause any issues yet. I incidentally stumbled upon this while trying to fix the center diff lock system. I was trying to get to the center diff lock relay - more on that in another thread. While trying to get to the relay I touched some of these wires and I had the ignition on so I could actually hear the fuel pump slow down, and I also felt how these wires were hot.

I am out of words. I've never seen anything like this done so poorly. I don't fully understand what they tried to wire in there. It looked like there had been a theft protection system installed before. I assume part of this mess was because that system failed and someone tried to get the car going again. There was something more, other things that at some point were wired in that were now just dead end cables.

I was shocked. I hope I'm not going to find any more things like this in the car...

 

[jpoole]

That looks like it was just waiting to fail and potentially burn in the process. Finding and fixing those wiring issues is a huge win for the reliability of your 80, nice work!

 

[TurbodreamZ]

I was having the same issue.. it was a pain diagnosing it but in the end, the truck has all new fuel components .

I noticed it ran worse during the hot Texas summer months or if I opened the gas cap to refuel. the problem was made more confusing because of an evap issue.