Intermitent No Start issues -FPR Related.

Z

Zarati

Well-known member
Nov 16, 2004
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Spokane, WA & Belize Central America
Truck doesnt want to start when cold (or not run for a while). Its clearly an electrical issue related to the Fuel Pump Relay (FPR) (EDIT). Holding it in my hand sometimes I can feel it click over, sometimes not. So I replaced it. Same thing. Now I'm thinking its whatever fires the relay. If I turn the key on, then slowly turn to start I can hear the relays clicking on and off. Sometimes I get no start. Then randomly I'll hear the FPR Click and it will start. Same symtoms with both old & new relay.

What next?
Replace the Ignition Switch?

My key has been fubared for many years but last time I checked a complete ignition switch assembly was like $250.00 Any leads on better pricing.

Can you re-Key a new one to match?
 
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D Chapman

D Chapman

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Jan 3, 2005
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On Kennith's private island
ptschram said:
While I've only seen one MFR fail, Chapman may well be correct.
Click to expand...


No no. I'm not saying the relay is his problem. I don't think it is. I think he's saying the "FPR" is a Fuel Pump Relay.

I think the only reason the fuel pump relay "sometimes clicks" is because the system is already charged and the pump does not need to run because the system is already pressurized.

With the very little info we have to work with, I'd suspect the alarm ecu. But that's only a guess, and not even an educated guess at that. Just a guess.
 
ptschram

ptschram

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Sep 27, 2004
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D Chapman said:
I think the only reason the fuel pump relay "sometimes clicks" is because the system is already charged and the pump does not need to run because the system is already pressurized.
Click to expand...

There is no feedback from the fuel system to the ECU-the ECU has no way to know the fuel rail is pressurized. The fuel pump will turn on for a few seconds every time the key is turned regardless of presence/absence of fuel pressure at the rail.
 
jhmover

jhmover

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Apr 23, 2004
5,571
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California
My D1 was doing that. Would start then mysteriously wouldn't, then would start etc...turned out to be the fuel pump. Put in a new one and never a problem since.
 
Q

Quentin

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Mar 19, 2006
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Cape Town, South Africa
ptschram said:
There is no feedback from the fuel system to the ECU-the ECU has no way to know the fuel rail is pressurized. The fuel pump will turn on for a few seconds every time the key is turned regardless of presence/absence of fuel pressure at the rail.
Click to expand...
Yep, my fuel pump primes for a few seconds everytime I turn the ignition on
 
Z

Zarati

Well-known member
Nov 16, 2004
328
0
Spokane, WA & Belize Central America
Yes I meant Fuel Pump Relay when I said FPR.
I wasn't saying I could get a new Lock assembly for $250.00. Just that I recalled them being expensive and didn't want to just throw money at one if not needed. The lock cylinder in mine is messed up though so I probably should get a new one anyways.

I suppose the next thing to do would be check the in & out signals from the Relay. Make sure that power is getting to the trigger when I turn the ignition on. I'll go load up my Wiring Diagrams and see if I can track that down and then report back.
 
Z

Zarati

Well-known member
Nov 16, 2004
328
0
Spokane, WA & Belize Central America
I've checked pressure and Delivery. Fuel Pump is actually brand new as the old one was shot. This problem is much more "Immediate". I"m pretty sure its electical. Just not sure what. When it fires it will fire and start right up. Then just DIE. Its died on the freeway a few times. Sudden, immediate complete power loss. USUALLY once its running it stays running which I am assuming is the extra voltage from the alternator helping overcome whatever bad connection is causing it. Seems to start better when hooked to a charger too. And yes the battery is fine. Brand new Optima.

Couldn't find the Multimeter tonight. But I did play around a little more. I think I might have confused my Relay's and this may be the identical looking one that powers the ECU (Engine Control Load Relay). At least I'm assuming it powers the ECU. I say this because I can hear the fuel pump cycling on and off.
-Turn Ignition to ON position. Relay Clicks, Fuel Pump primes for 3-4 seconds, Relay clicks off. So I think that the one causing my issue is the other one next to it. Sometime I can feel it click, sometimes not. When i do it seems to start fine. If I dont feel it click, no start.
 
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Z

Zarati

Well-known member
Nov 16, 2004
328
0
Spokane, WA & Belize Central America
Freaking Great. Problem is back. Never really fixed it. Temp warmed up and it went away. Been driving it all summer. Now it stranded me for the 2nd time this week. Luckily both times just down the street. Usually once its warmed up its fine. Actually, usually once it starts its fine.

*Its definately electrical.
*I've replaced both relay's. (Fuel Pump & ECU) They are next to each other and when the problem is acting up swapping relays or putting in known good ones doesn't help.
*I have noticed that when its not starting the fuel pump relay wont click back on when cranking. It will click over and run the Fuel Pump when I turn the ignition to ON, but then nothing.

SO... Where does the trigger signal come from to run the relay? I want to trace that wire down.
Also, where is the ground for the relay. I want to clean it up. The problem seems to go away when the battery is warm, or the car is on a charger. On a warm day, its fine. My assumption is that when the temp drops, battery voltage drops just enough that whatever connection is corroded (another assumption) it cant bridge the corrosion.

IDEAS???
 
Z

Zarati

Well-known member
Nov 16, 2004
328
0
Spokane, WA & Belize Central America
ptschram said:
Year and model would be of great help here!
Click to expand...

94' Discovery. Distributor Ignition.
Has the Two Relays for Fuel Pump and ECU to the right of the Passenger Footwell (Right Side).
I've determined its not the Relay's themselves but its related somehow to the circuits that the Relay's are in.

Fuel Pump itself was replaced last year.
Not sure if this helps but I think I noticed a correlation between the no-start & the relays.
I've known for some time that when it would not start the Fuel Pump relay seems to not turn on when the key is in the start position. I've also noticed that it seems (By holding the relay) that the ECU Relay also does not click when the Fuel Pump relay is not clicking. I need to do some more tests to verify this. Test light is broken but am picking one up tomorrow AM to do some more probing and start checking grounds.
 
Z

Zarati

Well-known member
Nov 16, 2004
328
0
Spokane, WA & Belize Central America
Ok. Got my Test light and a wiring diagram. It looks like the trigger wire for the relay is actually the ground which is triggered by the ECM. The Relay has power and is switching over just fine when I turn the key to the ON Position (3-5second Prime). But then when I go to start the car it is not signaling the relay to close. This is a Blue/Purple wire going to pin 85. The wiring diagram shows this wire goes direct to the ECM. So either.
A) ECM is dead
B) Whatever input to the ECM that tells it ground the fuel pump is screwed.

So where does the ECM Get the signal to ground the Fuel Pump? Does this come from the Ignition switch direct or through the "Main Engine Control Load Relay" that sits right next to the Fuel Pump Relay.

Any help much appreciated. I have to get this issue solved. Truck is grounded. Have a low mileage 3.9, Crower Cam, and some other goodies to put on it but no sense doing that if it doesn't run. ;-)
 
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Z

Zarati

Well-known member
Nov 16, 2004
328
0
Spokane, WA & Belize Central America
Damn, Now dont I feel like a dumb ass. Just went and checked &
NO, No Spark.
The symptoms were so similar to when the Fuel Pump Relay WAS frozen, that I thought it was related. Previously I had spark but no Fuel. Replaced Fuel Pump relay and it ran fine all summer.

I'm going to go dig around the ECM and make sure its got power, ground etc. Is it safe to assume that if it was a Coil or ignition component that the ECM would still turn on the fuel pump while cranking? Just checked all connections in engine compartment and all looks good.
 
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