truck dies wile running

[Cristina]

Hello,

 

I have a 1985 Nissan 720 4x4 truck recently upgraded with a European Weber carburetor by a professional mechanic. The truck has been tuned-up with new spark plugs, fuel pump, fuel filter, relay switch, etc. The truck was running great; however, now it sometimes just dies while running and won’t restart. After sitting for about 30 minutes, it starts again. Any ideas? Thanks for helping

[datzenmike]

Relay switch?? Is that the fuel pump relay that you mean? If so put the old one back in and try it. The 720 pump relay works but they often go bad over time. When the truck refuses to start can you hear the fuel pump working???.

[Cristina]

datzenmike, thanks for your rapid reply.  My name is Gregory, I am Cristina's mechanic and friend.  For the record, I am a professional.  I run my own shop and have been turning wrenches for a long time.  She posted the original question and then realized the issue is over her head so I am taking over.  Hope that's okay.  Let me clarify the sequence of operations on the truck so far.  When she first got it, the area needing the most attention was the front end (steering and suspension).  While taking care of that I noticed it had some funky wiring issues.  Nothing crazy, especially considering it's age.  There were a few things unplugged underneath but most notably there was a jumper wire run to the fuel pump directly from a switched source.  Probably to bypass the relay.  I tested the relay and it seemed to be working fine so I reconnected it.  At this point, Cristina had already replaced the fuel pump and filter on her own.  I figured those components must have been the problem all along.  After reconnecting the relay, the truck ran fine for my test drive and I gave it back to her.  Then her intermittent stalling issues began.  The truck would run fine and then just die out.  about 30 minutes later, it would start and run fine again for an unspecified period of time.  According to her, there didn't seem to be any rhyme or reason to it.  Not when it was particularly hot or cold or long or short distances or stop and go vs. highway.  It is also worth noting that the carburator situation was a mess.  Over the years, vaccum lines and switches, etc. had been disconnected and rerouted.  A common picture in vehicles of this era and I am sure you are familiar with this.  She had already planned on upgrading to the Weber carb so I said let's start there and see if that fixes the problem.  When I did the carb swap, I also dropped the fuel tank to check for debris and blew out all of the lines to eliminate that as a potential.  Everything was clean.  The carb swap was smoothe and when I went to fire it up, there was no signal to the fuel pump.  The relay was definitely not coming on.  I figured I caught it in action, so to speak, so I put in a new relay.  At the time I didn't know about the easy fix.  Just when you think you know all the tricks.  Truck fired right up and was driving really well until a few days ago when it randomally died again (same issue as before).  At this point I am convinced it has something to do with the relay situation, especially considering the chronology of everything.  Ran with jumper wire, removed jumper and died intermittently with stock relay, replaced relay, ran for a month and started to die again.  I asked her to leave the key on the next time it dies, roll to a safe stop and get out and check if the pump is still on but she hasn't had that opportunity yet.  Today I checked continuity at the relay plug to ground and the oil pressure switch, all good.  I also checked voltage from the ignition switch, starter switch, and the alternator, all good.  I pigtailed the ground to a ring terminal right on the screw that holds the relay to the body under the dash.  Just to eliminate that one.  That didn't work because it died again on her way home.  I ordered a new oil pressure switch that Cristina will put in today, although I am not confident that is the issue.  I don't think low oil pressure is the issue either because the truck runs and sounds really strong and smoothe and the oil looks good.  At this point, I think it is something in the wiring harness and if the oil pressure switch doesn't fix the problem, I will just run all new wires and a new relay that just supplies switched 12v to the pump directly.  Unless you have a better idea.  Can low voltage from the alternator cause this kind of problem?  Any help or suggestions would be great.  Sorry for the long winded story, just wanted you to have all the info.  Thanks for your time.

[supererogator]

Has the tank been flushed?  Silly and simple answer, I know, but I know this cleared mine up a bit.  Sediment and all…intermittent dying and odd running….

 

[datzenmike]

Here's the article on the relay for the pump.... http://dlarson.hubpages.com/hub/The-Datsun-and-Nissan-Pickup-Fuel-Pump-Relay-What-the-Haynes-Automotive-Repair-Manual-Wont-Tell-You

 

 

You can run without the relay. What it does is shut the pump off in the event of an accident. Engine stalls, no alternator... no pump. It will also shut off if your oil pressure drops and the light comes on... kind of handy.

 

 

 

 

 

Has the tank been flushed? Silly and simple answer, I know, but I know this cleared mine up a bit. Sediment and all…intermittent dying and odd running….

It's in his text...

 

When I did the carb swap, I also dropped the fuel tank to check for debris and blew out all of the lines to eliminate that as a potential. Everything was clean.

[Cristina]

Hey every one, Cristina here. Here is the thing. The truck is awesome. This machine will take me to places where others can't get to. I have been spending much time in the desert of the Baja California, in other words, bad bad bad rocky sandy steep roads... Amazingly I did all of that with my 4x4 Toyota Tercel, which I am slowly destroying, even with the lift and bigger tire, there only is so much the poor little machine can do! Now, I am soooo happy with the 720. What an upgrade! Not only I'll get anywhere I want to but, I will have fun wile doing it.

 

Much work and $ has gone in to it but it is well worth it. It's a great Truck! and I love driving it! The problem at hand, ‘it dies wile driving’… What the hell??? We have done and checked every thing! (as my mechanic and friend explaine) So I come to you guys for advise (thanks for the fuel pump article lead) And even though I don’t know shit about mechanics here is a girls gut feeling… I really think that this problem is a ‘silly’ thing! Some switch or hose or or…

 

Any other ides, suggestions will be much much appreciated.

 

Thanks,

Baja Girl-Fall is coming time to pack up and go back South to Mexico lindo.

[dr.feltersnatch]

Sounds like an ignition module that is starting to fail.

[JoeCool]

hmm... you mentioned STEEP roads, how steep? Like mountains? If so could it be a high altitude issue?

[datzenmike]

Very simply, in order for an engine to run it only needs fuel and spark.

 

FUEL

Next time it quits, quickly shut it off, lift the air filter and look at the small round glass on the front of the carb. The fuel should be in the middle, at or near, the white dot. If empty, then this is a fuel delivery problem... likely the pump (for w/e reason) not working. As the pump was replaced it is possible that the new one is faulty. Over heats, shuts down. There will be a filter between tank and pump too I believe. If there is fuel try SPARK, below

 

SPARK

If there is fuel. Pull high tension wires off the coils at the distributor cap. Place an old spark plug in the end and lay on a grounded surface. Crank the engine over... is there spark? Try the other coil. If spark try FUEL, above