Fuel Pump Failure?

[Duner]

OK, my apologies as I'm sure this has been covered before, but I do not have the time to search and review all of the threads.

 

Intermittent response from fuel pump. The truck died on the highway (while my dad borrowed it, so I can't be blamed) no audible response from the pump. Triple A towed it home and still no response, then like majic pump kicks on and truck starts.

 

It ran for a couple of minutes then my dad goosed it and when it dropped back to idle it died and again no fuel pump response when the key is turned.

 

Haynes fails to identify the fuel pump relay and says the dealer should check the operation for you. Anyway swapping the relays has brought no improvement. The fuel pump still fails to come on.

 

What voltage should be present in the fuel pump/sending unit connector when the vehicle is in the start mode?

 

I'm reading 7.5 but I'm going to try grounding in a different location.

 

I thought that the pump is to receive 12volts at start then drop off to 8 or 9 volts while running and yes the resistor is good (measured 3.75 volt drop across terminals) and bypassing the resistor still produced no response in the pump.

 

So before I lay down money on a new pump is there anything else I should check for and does someone actually know which relay goes to the fuel pump on a 1990 4.0?

[Pete M]

I'm guessing that it needs a better ground. Mine was grounded to the tiny screw behind the drivers side tail light.

 

Also, be sure to review rule # 2: :thumbsup:

 

http://comancheclub.com/forums/viewtopic.php?t=1239

[FxRacing282]

probabally not your relay. when your fuel pump goes junk you can usually hit the tank or pump a few times and its like a get out of jail free card. id say check EVERY connect and clean and re connect. also check your fuseable links.

[jmaxj]

mine was doing the same thing in my xj and mj so i pulled the pump yo replace them and found that the rubber pickup tube was off of the metal part, hose clamp was still on the tube so i just put it back on and they work fine the xj's has been like that for about 2 yrs now and the mj a couple months.

[Duner]

Ok, pump was dead, replaced with autozone special, I think it's designed for the xj and not the mj required some fitting to make it work.

 

Anyway truck started and now runs at 3000 rpm. (isn't life great) disconnect IAC, TPS and MAP no luck.

disconnect everything again and pull throttle body and give a light clean up re-connect and idles at 750 rpm.

 

The Renix is fantastic but I don't think we will ever no why unplugging sensors would fix this or why it periodically does it to begin with.

 

Anyway one fuel pump/sending unit/filter and can of carb cleaner later and she's back on the road again.

[FxRacing282]

Ok, pump was dead, replaced with autozone special, I think it's designed for the xj and not the mj required some fitting to make it work.

 

Anyway truck started and now runs at 3000 rpm. (isn't life great) disconnect IAC, TPS and MAP no luck.

disconnect everything again and pull throttle body and give a light clean up re-connect and idles at 750 rpm.

 

The Renix is fantastic but I don't think we will ever no why unplugging sensors would fix this or why it periodically does it to begin with.

 

Anyway one fuel pump/sending unit/filter and can of carb cleaner later and she's back on the road again.

DON DON DON probabally had some poor connections and the friction when you pulled them and cleaned em got the crap off