JPTL

Last month, I went to take my GT out for a spin and it just cranked. Usually it starts immediately, even after sitting for extended periods of time.
Guessing that it was fuel related, I listened for the whirr of the fuel pump after turning on the ignition and heard it for sure. It sounded a little louder than I recall it sounding, but that might be b/c I was listening for it. Still, I swapped out the pump relay with a brand new one. Still no start. Serves me right for allowing this car to be a garage queen, but that's another story.
Kevin Lacy suggested that I take the little end bolt off of the fuel rail and see if there's any squirting or at least dribbling. Nothing there. Seemingly dry as a bone.
I pulled the hose attached to the sender and that too was dry


(I'm assuming that this is a vent hose, not a fuel delivery hose, but I'm still adding this).


I held my cigar in my other hand (just kidding) unscrewed the cap from the sender unit - if that's what it's called, and nervously (not kidding) took a peek into the tank to see what I could see.

I could see the internal pump,



I can't imagine any way that I can determine if this pump is working or not simply by looking into the tank.
Is there a sequence to troubleshooting a fuel delivery problem and/or isolating the internal pump from the external and testing each before draining and dropping the tank? I'm assuming that the problem is in or around the tank.
Are there separate relays for each pump (maybe I swapped out the wrong relay).
TIA,
J.P.

ROG100

The internal pump looks to be in roughly the right position. If the short rubber hose has failed it will be lying crooked.
Light your cigar again and pull the hose from the external pump to check for debris.
Jump the fuel pump relay and check for flow from the internal pump into a bucket.

Also try reversing the connections on the external and see what shoots out the back.

You may need to drain some fuel out of the tank.

FredR

JP,

You should not go anywhere near the fuel tank with a lighted cigar you nerd- quickly throw the thing into the tank to extinguish it and never do that again!!!!

Now the more intelligent discourse [hopefully]-

If you are sure you can hear a pump running then try to ensure it is the external pump that is running- you can measure the voltage on the pump terminals whilst cranking to make sure the LH unit has not failed - not the case if either pump is running or you have voltage.

As Roger says the in tank pump connection hose can fail and a small chunk of rubber is all it takes to jam the main pump impeller- a reversible condition. The stock piece does not last that long and Roger has a GB kit to rectify this problem but you have to remove the in tank pump to fit it.

Plenty of discussion about the in tank pump and whether it is needed including Andrew's thread currently regurgitated. I am from the "needed" school of thought but then I live in a hot climate where my operating conditions are on the limit.

As Roger suggests you can try running the external pump with the discharge disconnected and measure the flow but if the rail was dry and you have power at the pump I suspect it will be prudent to plan on removing the pump.

If the pump does not spin you can try to reverse the polarity on the pump very briefly to spin it backwards and see if it frees up the impeller but again I personally do not like that idea with the pump in-situ. If this was to free up the pump it probably means the in tank pump has to come out anyway to resolve that issue.

Rgds

Fred

SeanR

Just dealt with this on a '91 yesterday.

Internal pump crapped out, jammed up the external so no flow.

That hose you have pictured is the return line and you should have fuel flow back to the tank there. It's also a good place to access a FPR failure by clamping it off there.

worf928

If the fuel pump can deliver fuel, bypassing the FP relay will allow the pump to operate. In this condition, with the engine not running, you would be able to hear the flow of fuel through the fuel rails.

If I read the above correctly...

If your fuel pump turns on with the ignition - and not only after you start cranking the starter - then your LH ECU has failed.

Besides everything else written in this thread - all good except the Cigar stuff - if your fuel pump is running and delivering fuel, a failed LH may not ground the injectors. That's what causes them to deliver fuel to the cylinders assuming there's fuel in the rails.

jcorenman

This ^^^

The PSD (90+ cars) pump runs on key-on, before the engine is cranked, and is often mistaken for the fuel-pump. As mentioned, the fuel pump waits for the engine to start cranking.

That return hose at the top of the tank is the place to do the fuel-flow test outlined in the WSM: Connect a hose extension to that hose with a coupler and a couple of clamps, 6 feet or so to reach outside the car, into a empty jug or gas-can. Jumper the fuel pump at the CE panel for 30-seconds, then measure how much fuel got pumped: It should be 1.25 liters, or 1/3 gallon, or 2.0# or 0.9Kg (net) on a small scale.

JPTL

Thanks for all of the replies so far -

I do hear the PSD initially power up at ignition on. That's more of a buzz sound coming from the rear and is louder than the sound a fuel pump would make. It abruptly turns off after a couple of seconds.
I also hear an electronic "fluttering" sound that briefly comes on at about the same time, then stops after a couple of seconds. I thought that this was the fuel pump. After a few seconds there is no sound with ignition on.

dr bob

J.P.--

Similar symptoms for me turned ut to be a weak fuel pump relay. Following the JB mantra "relay-relay-relay", start off with that because it's a lot easier and safer than fiddling with spilled fiuel and sparks. On my car, the pump made noise and initially fooled me. Testing with the fuel pressure gauge and a jumper reminded me what the pump was really supposed to sound like. New relay brought it right back to life, I'm happy to report.

For those playing at home, the fuel pump relay, the LH/injection and EZK rlays are the ones that can strand you. They are also the least expensive, and relatively simple to change them all now in the comfort of your own garage or driveway. Much better than headscracthing along the side of some lonely highway with your SO, and that horrible screeching noise in your ears.

JPTL

This issue is new to me and unfortunately I don't have the space to start troubleshooting and learning about this issue over the course of a couple of weeks, so I'm using you guys to help me prepare for what I need so that I can get the issue nailed in a short period of time. Your cumulative advice is as always invaluable, so thanks!

I'm going to start by second guessing myself and re-checking the relay. Taking the "relay-relay-relay" advice as gospel, I've replaced a seemingly good original relay with a NIB Werhle 20 240 073 (box labeled 141-951-253-B) so I believe that I'm using a good, correct relay and have hopefully eliminated what often seems to be cause #1.
From what I'm reading here, I might first want to do an electrical, followed by a physical diagnostic of the external pump and it's power circuit before I drain and drop the tank.
So after I put my cigar down, I'm gathering that the first step would be:
1. Test the relay by getting a voltage reading at the pump while cranking the engine. If I get 12v, then the relay is good and proceed to Step 2. If no voltage, then the relay or wiring is suspect and start the troubleshooting process unrelated to the fuel pumps themselves, the tank and all related fuel lines.
2. Bypass/jumper the FP relay*, and take a voltage reading at the pump terminals - ignition on. If the I get a 12v reading but the pump isn't operating, the FP is jammed with debris, or it has simply failed. Skip step 3 and go to step 4.
3. If the pump appears to be operating, then per Jim, get a measurement of fuel flow at the return hose.
4. If the FP is operating but there is no flow at the return hose, then drain the tank.
5. Check for blockage between the tank and the FP, starting by removing the feed hose from the tank to the FP (#4 in the schematic).
6. If feed hose is deteriorated to point of complete blockage, check for debris in the FP and replace the feed hose. Even if it's not deteriorated, replace it.
7. After the feed hose has been replaced, before reconnecting the fuel pump, attempt to clear debris from the FP by briefly operating it in reverse.
8. If after the FP has been reinstalled and the system primed, the pump is not adequately pumping (volume test), the FP is defective - replace along with a new filter...
...or start troubleshooting the internal pump.

Please feel free to amend or correct me with any of my steps here.




*is the corrrect method of bypassing XXVI relay with a constant-on fuse-protected circuit connecting 87 and 30?

JPTL

My first test was to read the voltage to the pump, new relay in, during cranking.
Nothing, nada, zilch.
I jumpered the relay, connected the battery and the pump kicked on and I got a reading of 10+ volts at the pump. Since the pump was still connected to the fuel lines, I immediately disconnected the battery.
Replaced the relay with another NIB relay (same Werhle 20 240 073) cranked the engine and again, no voltage.

What now?
Can this be anything other than a bad LH?
Also, not really knowing what an LH does, I assume that if I suspect to have a bad LH, I shouldn't try to start the engine with a jumpered relay.

John Speake

Have you checked that there is fuel pressure when you jump the FP relay ? I didn't see that you had...

If you do have fuel, then for some reason the LH isn't getting the RPM signal that wakes it up. That signal is provided by the EZK(ignition) ECU.

So you need to check for spark, then work from there.

JPTL

I didn't check for pressure at the fuel rail, but after the pump ran briefly after jumping the relay, then replacing the relay and trying to start it, it did kick over for a second, telling me that for the brief time that the pump ran, fuel got to the rail. Prior to jumping the pump relay, I wasn't getting as much as a hiccup.
So going on the assumption that pressure is getting to the rail when the pump is running, does the EZK ECU circuit control the pump relay circuit as well as ignition spark?
Is the next step looking at that XXII relay?
On the '91 it's the relay with the fuse tester (928.615.203.00) can this be swapped out with the same relay as the fuel pump and the LH-Jetronic Fuel Injection (141.951.253.B)?
I did swap out the LH-Jetronic Fuel Injection relay on a hunch.

I'm now rehashing my question. Since the engine did briefly kick over after I got fuel to the rail by jumping the pump relay, then putting the relay back in and cranking, it had to have been getting a spark.

John Speake

It's the LH ECU that controls the FP relay. But the LH won't do that until it receives a rpm signal from the EZK ECU.

Your tests do suggest that the fuel system and EZK may be working OK, and that the LH ECU could be the problem.

You might save time by having your LH ECU tested in another car if you have someone handy who is OK to do that. Or borrow a known good LH.

Yes the relay tester EZK relay can be swapped for the "53" type relay but I think we're passed swapping relay now...

worf928

In the absence of methodically following the steps in the LH/EZK Troubleshooting Guide, I agree: get the LH tested. You can send it out also, if there's no one close by that has a working '87+. (And yes, any know-to-run '87+ will do.)

John Veninger

My vote is the LH.
As mentioned, see if anyone local would do a swap with you to verify.
Is your LH is the original one from Porsche? Appears the "newer" LH computers have held up better than the early ones, but that's just a feeling.
John and/or Louie could give us actual data as to the the quantity of failures they have fixed by year.
My 90GT still has it's original and have been thinking about sending it to Louie before it fails.