fuel pump

[cessna]

Hey everyone been trying to figure this one out. Just last week my 1993 z34 has been random stalling on me, sometimes it will restart right away, just recently this time when it stalled out I had my fuel pressure tester with me and took a reading and had no  pressure at the rail so of course the car would not restart.  I tried switching the relay out with another and still no pressure. I couldn't listen for the pump to run as I was on the side of the road to much road noise to hear it. So I left the car for about  hour came back with some tools and to no avail turned the key to the on position and the rail built pressure and she started right up seems to have a slight lope to it. My question is would the fuel pump just die and cause this random stalling when its hot out and then come back to life  or am I chasing another problem.  

[55trucker]

You're chasing another problem

[cessna]

55trucker, So the fuel pump wont stop in random acts like this and not provide pressure to the rail , the wife was saying  when she last  drove it that it would surge now and then when she drove at speeds around 50 or so. It just started acting like this about a week or so ago when she told me it stalled on her when making a slow turn but it restarted and she drove it home, Its stalled twice again according to her over the week and that's when I drove it the other day and it stalled on me and I checked the fuel pressure and it was reading zero at the rail so I was thinking fuel pump cutting out when it gets hot , So maybe ICM shorting out when it gets hot causing the pump to stop running ?  

[55trucker]

The ICM doesn't control the fuel pump, the pump circuit is controlled be the ECM thru the fuel pump relay.

Without spending any money on this at all.......to  begin with let's do a simple test to the fuel rail.

take a pair of vise-grips (relatively small ones) & pinch off the fuel return line back to the tank. The fuel lines are under the throttle body. Be gentle when doing this, one just wants to put a noticeable restriction in the line.

Now do the pressure test again. What does your gauge read?

not  sure what you're referring to when you state *the fuel pump won't stop in random*

 

Edited July 29, 2022 by 55trucker

[cessna]

I was referring to the idea that since I stated that the fuel pressure was at 0 when I checked it at the time of the stall, that maybe the pump is dying randomly and when it cools down that it will restart. I just went and retrieved it from the side of the road after sitting there all night, it built pressure back up and started fine, idle was high around 2k for some reason ?  I noticed when I got it home the idle is surging up and down I have checked for vacuum leaks and as of right now nothing found this just started after this last stall with surging idle . I'm sorry I meant to say ECM not icm in my earlier post. I will give your test a try should I just energize the pump for pressure and see what it is or actually start it up and let it run for the test. 

[55trucker]

Just do a regular key on *prime the pump* with your pressure gauge in place & see what you get.

The pressure should be approx 42lbs, the pressure should hold, just crimp off the return line to restrict the return pressure. With the gauge still in place release the crimp, if the pressure is not holding consider the FPR to be in question.

Usually when the FPR fails the internal return spring goes, the diaphragm tears & fuel gets into the intake via the vacuum hose.

[Schurkey]

The fuel pump can ABSOLUTELY be failing semi-randomly.  Pumping...not pumping...pumping again.  Usually this is accompanied by generalized low pressure, so you get low pressure, no pressure, low pressure, etc.

I dealt with this on my '93 Euro 3.4L, 1600 miles from home.  Took me 8 hours to drive the final 130 miles to my destination--most of that time stalled on the side of the road, in minor mountains, on a holiday weekend where the uppy-downy-curvy highway was filled with boats on trailers and overall heavy traffic.  IF I could get the car started, and IF I could get above 40 mph without stalling, I stood a good chance of getting to 70 mph where the engine ran pretty good--minor misfiring and poor throttle response, but it would hold speed nicely.  Anything below 40 mph probably meant the engine would stall.

The folks who replaced the fuel pump said my fuel pressure that should have been 40+ was actually 8 psi when the pump was working.

 

Having said all that, there are other potential causes of low/no fuel pressure randomly.  You're probably going to need to do some more diagnosis before condemning the fuel pump.  I'd be verifying the voltage as close to the pump as practical, and also looking for voltage on the pump ground.  Any voltage on the pump ground is subtracted from the supply voltage, that's what the pump is actually "seeing".  For example, engine running, alternator puts out 14.2 volts.  Fuel pump voltage at the connector just before the harness goes up 'n' over the fuel tank is 10.2 volts--a full 4 volts down from system voltage (excess voltage drop.)  Making things worse, you have 2 volts on the ground wire (Excess resistance to ground) meaning the pump is actually working on 10.2 - 2 = 8.2 volts.

 

It's not unusual to see 2 volts of voltage drop on the supply side, and one volt on the ground side--GM USES UNDERSIZED WIRE for the fuel pump.  More than that is a problem.

And don't forget that the wire harness for the fuel pump/sending unit IN THE TANK can be corroded/faulty, too.  I always replace the in-tank harness along with the filter sock when changing a fuel pump.

Corroded wire end from original in-tank fuel pump harness, compared to replacement:

 

Replacement harness available at any parts store, tends to be longer than original to assure it fits as many vehicles as possible.

 

Edited July 29, 2022 by Schurkey

[GTP091]

I lost an injector last year on my GTP.  Nothing to do with your issue but i learned a fair bit in the fix.  I hadn’t ruled out the FPR initially in my troubleshoot or the pump.  If you can catch this in the act and pinch the return line that would be much easier than crawling under the car to test voltage.  Of course when it’s doing this hopefully you could just hear or not hear the pump, ideally in your garage.  Could be the pump or FPR or something else.  The intermittent part of this would push me to an electrical issue in the pump wiring.  I’d rather pull the plenum, fuel rail and replace FPR than drop the fuel tank so hope for your sake it’s not the pump.

Best of luck man.  I have GM service manuals if you need some specific info.  

[cessna]

Thanks for all the response,

 It was raining all day yesterday so no chance of doing any testing but today looks great, heading out to check a few items that 55 trucker brought to my attention.

Great to hear from you schurkey hope all is well on your end and yes I was also thinking pump and wiring will defiantly be something to check also,  but after 55 truckers comment it got my mind back on troubleshooting more before the fuel pump jump.

Gtp thanks for your input and offering up manuals I have manuals but we are in the middle of selling our home therefore most items are packed up including a lot of my tools and also can't really get into a large teardown with all the traffic of showing the home timing is a real PIA on this one for sure.

Thanks to everyone for giving some helpful info on this as my mind is not really on diagnosis of a problem car right now but got to get it back on the road one car is making it difficult for the two of us right now.  I will let you guys know what I come up with on some further testing . Thanks again    

[55trucker]

Are you seeing any codes flash on the check engine light?

Another possibility is the MAP sensor, if the sensor is questionable or the circuit is dodgey the ECM cannot properly configure the needed air fuel ratio because it doesn't know what the ambient barometric air pressure is & will lead to what you're describing. You'll get hard start/ no start/stalling.

But there usually will be a code 33 or 34 for the MAP.

[cessna]

Hey trucker 55,

I've been running several test on it for the last couple of hours the fuel pressure is around 40 psi when key is energized. I left it sit for about a half hour to see if it would deplete, nothing it held tight, so I decided not to pinch off any lines so I started it, it fired right up let it run for a bit, idles great, pressure around 38 to 40 rev it up pressure climbs up about 6 or so psi drops back to 40 and holds tight. I removed the vacuum line to the fpr and the pressure climbed up around 6 or so psi plugged it back in and it returned to normal 38-40 psi I did that several times finally shut it down and let it sit for an hour and a half with gauge hooked up and it never dropped pressure, Started it back up runs fine no mis, no surge or anything. I left the gauge hooked up until the wife gets home and I will check to see where it is and hopefully take it out and run it and see if I can get it to stall again. 

I am baffled with this one but like your saying maybe the map sensor? every time it acted up it was hot and humid outside from what I remember. I replaced the fpr 2 years ago according to my records it was a bwd brand so not sure how well it holds up couldn't locate a delco one at the time but have one now  but doing all the test today everything is holding tight. I just cant understand why when it stalled out the other day and I jumped out and hooked the fuel  pressure gauge to it, it read zero pressure and cycling the key on and off it never built pressure I couldn't hear if the pump was running due to traffic driving by me on the road.   but when it cooled down an hour or so later I turned key on position and  pressure built up and it started. So that's why I was thinking fuel pump getting hot? and not pumping. I don't know what to look at next that will tell me anything. 

 Oh I hooked up my code reader to it and it didn't show any codes pending but not sure if the obd1 is the same at storing codes like the obd2 is.

[55trucker]

The pump being inside the tank shouldn't be affected by heat or humidity, the pump is immersed in fuel, the fuel keeps the pump cool.

Does this *only* take place when the fuel level is low? I mean low as in near empty.....

keep a 14ga short jumper wire in the car, next time this occurs pull the relay, bypass the relay functions, go straight from the battery terminal directly to the pump terminal.

The relay is on the left side shock tower, standing beside the fender viewing the relay module with cover off....battery is at 3 o'clock, pump terminal is at the opposite side at 9 o'clock.

do you hear the pump spinning?

 

 

[cessna]

That will be something I will try, remove the pump relay, jump it from positive on battery to plug on pump terminal I believe there is a wire with a connector sitting there now for testing I assume.  I will have to check.  will let you know what happens when and if it fails again. Thank you, Trucker55

[cessna]

I forgot to mention that the fuel tank is around 3/4 full when this happened I never let it get below 1/4 tank just for fear of picking up dirt and so forth from the bottom of tank 

[cessna]

Well its been a couple days seems to running ok keep checking fuel pressure it holds, might drop 8psi in an hour and down to zero by morning but primes right back up with the turn of the key . So went to see about pinching off return line and found a bubble in the nylon line close to the connector looks like that could be a future problem seems to be a little soft there, can these lines be repaired or does it need to be replaced never dealt with the nylon fuel line.

[55trucker]

15 minutes ago, cessna said:

found a bubble in the nylon line close to the connector looks like that could be a future problem seems to be a little soft there, can these lines be repaired or does it need to be replaced never dealt with the nylon fuel line.

Duhhhhhhhh............you'll have to enlighten us here........where did you find *nylon* fuel lines?

The fuels lines are all steel except for the pair of flex lines under the throttle body (wrapped in split loom) where they are quick connected to the fuel rail......(see above photo)

[cessna]

Yes that is the lines I'm talking about. What is the material used for the flex line it has a bubble in the line near the connector when I pulled the wrap down  seems rather soft there I was thinking it is some kind of fuel resistant nylon material I've always dealt with rubber or steel lines. 

[55trucker]

The lines are simple single braided gasoline approved hose.

If you have a failing hose getting it repaired is going to be a bit of a challenge, the replacement hose is easy to get, one has to remove the old hose from the end of the steel line by undoing the union, then carefully cutting thru the crimped on collar (a small dremel tool works well), now one pulls off the old hose. The other end is the same, one has to keep the quick release fitting to go onto the new hose.

The hurdle is finding a shop that does A/C work including fabricating A/C lines. That shop will have the needed crimping tool to crimp the collars onto the new hose ends inserted into the quick-release fitting at one end & the steel fuel line at the other end.   

[cessna]

I definitely need to look into getting it repaired like I said it has a soft bubble in it so not something that needs to be ignored for sure. I will check at my local auto store or rock auto and see if they might have the line needed for the repair.  I did want to do the line pinch like you suggested but after finding that bubble I'm very hesitant to put any stress on those lines until I can find out about repair. Thanks again Trucker 55   

[55trucker]

I'm not in the states, apparently O'Reilly's has a hydraulic hose repair service, you might look into that or if where you live there is a hydraulic hose service shop that as well could be the answer.

[cessna]

I finally got some time to do some research and found that dorman makes a really nice nylon fuel repair kit with different size fittings and tubing looks easy enough to replace or repair also on amazon.

[Schurkey]

Remove damaged rubber section of hose from the metal ends.  Buy "fuel injection" hose of the proper diameter, having a pressure rating higher than your fuel system uses.  Cut hose to length.

Buy two "Fuel Injection" clamps to suit the hose.  Slide hose over metal ends, tighten clamps.

Done.

[cessna]

Yes I was looking at the smaller kit they have with the line and connectors fairly simple to assemble by the looks of it. What I like is that it lasted 30 years so it is pretty durable stuff, I guess I could change it over to rubber fuel line,  I've never had to repair the high pressure nylon fuel line before, but looks like they have several kits out for it now pretty cheap. I haven't had the chance to check voltage on the pump yet that's my next move, would like to drive it more and see if it still dose the random stalling, just been to busy with the house to get after it. 

[cessna]

Well looks like it turned out to be fuel pump, replaced it and no more random stalling will keep you guys posted if it comes back . Thanks for all the help .

[cessna]

Well fuel pump has eliminated the stalling effects I was getting, its been about a month now with no problems other than now the damn sending unit quit working.  Checked all wiring and gauge  no problems there. looks like pulling tank down again. not sure I want to buy Adelphi unit again, anyone have any recommendations on a decent unit to replace with this time around ?