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blocked FPR?


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11 replies to this topic

#1 mdcc2010

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Posted 23 March 2013 - 11:02 AM

So in my continuing XT saga, I'm still trying to get its fuel issues sorted. Symptoms were: noisy fuel pump after running for a few miles, runs fine at speed but with occasional stalls at idle, occasional flooding. Initially I thought it was the aftermarket fuel pump failing, so I replaced it with an OE pump. Then the car wouldn't start and was receiving zero fuel at the engine, so I figured the tank was plugged (there was some rust in it, and it had been sitting for a while before I bought it). In went a new tank, but still no fuel to the engine. Turns out my new pump had failed, so I put the aftermarket pump back in and it started, but the same symptoms remained: noisy pump, random engine roughness, flooding.
The only thing that hasn't been replaced is the fuel pressure regulator. Removing the fuel return hose at the engine and running the pump results in zero flow from the return pipe at the engine, and there's still no flow out when the engine is running, with or without vacuum applied to the FPR. Anybody have a FPR just completely restrict flow before?anything else I should look at?

#2 naru

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Posted 23 March 2013 - 11:39 AM

Fuel pressure is the first thing to check.
Doubt the FPR is stuck,but,anything is possible.
I also had no flow from the return line.New pump fixed that.

Check voltage and grounding of the pump.
Flow rate at the FPR feed line too.

FPR diaphragm OK?

Got good flow from the tank to the pump?Gas should pour out at a good rate w/the pump inlet is disconnected.

#3 Gloyale

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Posted 23 March 2013 - 12:46 PM

Test the fuel pressure both unregulated (straight loop from filter back to tank) and through the fuel rail with FPR hooked up.

 

Gotta have some PSI #'s or it's just guessing.



#4 mdcc2010

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Posted 23 March 2013 - 02:54 PM

I previously checked fuel pressure and it was a little higher than spec and didn't change much with the throttle applied. Fuel flows freely from the filter outlet when the pump is run.
I would bypass the FPR and then run the engine to see if that improves anything, but the stupid spider intake manifold has to come out first, and since it's only $45 for a new regulator i'd rather replace it because it wouldn't be worth the hassle to tear it down, bypass the FPR, put it back together, test it, and then do another teardown/rebuild cycle to either return it to normal or replace the FPR. The more i work on these things, the more i prefer the old flat mpfi manifold.

#5 naru

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Posted 23 March 2013 - 07:17 PM

Fuel pressure should be waay higher than spec. if there is no flow from the return side because of a stuck regulator.
I think you have a fuel delivery problem,not a FPR problem.
My bad pump had OK fuel pressure when checked at idle,but had no flow from the FPR return.Sound familar?
Your fuel pressure didn`t vary w/throttle because there never was enough fuel pressure/flow to open the FPR.

Edited by naru, 23 March 2013 - 09:29 PM.


#6 Gloyale

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Posted 24 March 2013 - 02:32 AM

Are you sure you have injector pulse consistently?  There is a known issue with the crimp joints in the injector pulse wires, where they run under the passeneger side carpet/rocker.  White/red and white/blue wires.

 

Just a thought.  Wasn't sure if you meant no fuel to the rail, or no fuel for fire to the cylinders.



#7 mdcc2010

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Posted 24 March 2013 - 10:39 AM

Thanks for the tip. There are one or two other random wiring issues to sort that will involve removing the carpet. The injectors seem fine; the car runs without too much trouble once it warms up. It's just that after it's been running at low speed for a while, it seems that the fuel pressure builds up enough to over-fuel the engine (i sometimes get puffs of white smoke when throttling up from idle) and cause the fuel pump to make racket. A few times the car has acted like it was flooded when started after sitting for a few hours, which excessive fuel pressure could cause.

#8 naru

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Posted 24 March 2013 - 02:12 PM

Sounds like a leaky injector and weak pump just like I had.
Does it hold fuel pressure overnight?

My fuel pressure was slightly high too.Made a weak pump a strange diagnosis.
I also suspected the FPR until I saw there was no flow from the return.

The lack of highly excessive fuel pressure combined with the lack of flow from the FPR return PROVES it is a weak pump or related problem.

#9 mdcc2010

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Posted 30 March 2013 - 04:36 PM

I resoldered the majority of the connector pins in the ECU and checked for leaky electrolytic capacitors; unlike Hondas' ECUs, this one has only two such caps and they weren't leaking, so I put it back together and reinstalled it. That, plus checking the harness more or less ensured that the pump's circuit is OK.

 

I didn't check fuel pressure with the aftermarket pump and the new tank (only with the apparently bad new pump and the old maybe-restricted tank), so I put the gauge on and ran the engine: pressure hit 80 PSI and pretty much stayed there until the fuel pump started overloading, at which point it dropped to about 50 PSI; no flow on fuel return at any point.

It didn't seem to hold fuel pressure for very long after it was shut down; it dropped slowly over several hours from about 30 PSI, and I figured it was either draining back through the pump or possibly past the injectors, since it obviously wasn't going through the return hose.

Removing the fuel supply hose from the engine and connecting it to a new FPR's inlet caused the gauge to register approx 36 PSI, with fuel flowing from the FPR's outlet when it exceeded that point. So it was (mostly) the FPR all along, which means I get to take off the stupid intake manifold collector to replace it :/

I'll probably test and potentially replace the coolant temp sensor (which may help my fast-idle problem) and also poke at the AAV to see if its shutter's sticking closed or something while I'm in there.



#10 NorthWet

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Posted 30 March 2013 - 05:34 PM

Just a dumb question:  Are you sure that you have the supply and return lines correctly connected at the manifold piping?

 

I only ask because some months ago I had some issues after an engine swap, only to find that I had connected the fuel filter's outflow to the manifold's "return pipe", and the chassis' return hose to the manifold's inlet pipe.

 

Embarrassing, but quickly rectified.



#11 mdcc2010

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Posted 30 March 2013 - 05:44 PM

haha, yeah, when I tried to start it up the first time after putting it back together, it wouldn't fire without starting fluid before quickly dying. Swapping the supply and return hoses got it to run.

 

This event wasn't the cause of the current problem since the car was having these issues before I tore it down. I'm not sure how the FPR stuck to the point where it won't pass ANY fuel. I'd guess it sat for quite a while without being properly stored before returning to service not long before I bought it. I mean, there were some dead vines that had grown into a few nooks and crannies in the underbody, so there had to have been at least a year of neglect involved.



#12 NorthWet

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Posted 30 March 2013 - 09:11 PM

I thought I recalled you saying that it was running previously; just thought it was worth the asking.  (I, also, eyed replacing the FPR on my spider intake and thought it would be a headache.  Luckily, my problem was mere stupidity.)

 

I have never had an FPR problem from the car sitting neglected for years (and their have been many...)  I rather doubt that this was the cause of your FPR's issue... but who knows?  Good luck.






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