Fun new gremlin -- 280 randomly dies... fuel-pump??

[KDMatt]

So I've finally started driving my Z again after about 5 weeks of extensive rehab. Today was her first day to the office and back home... About a mile from my house (on a slower main thoroughfare) the motor suddenly died. 

Some notes on the modifications that have been made to the car:

1 - The fuel pump shutoff has been bypassed, so the pump will begin to run as soon as the key is switched "ON" and continue to run until the key has been switched "OFF"

2 - The stock fuel rail has been removed in favor of a solid billet-aluminum one with an adjustable FPR that provides a fuel-pressure read-out. 

3 - The OEM fuel pump was replaced about 5 years ago with an aftermarket/universal one that has, until now, given me now problems.

4 - At the same time, the tank was pulled, given an acid-bath, and recoated/sealed. There is now a small plastic filter between the pump and the tank.

I just replaced the fuel pump relay with a NIB NOS one since my original one had been pretty mangled. The contacts on the pump are clean and all of my fuses look okay. Since the car had been sitting for a couple of years, the tank was drained and fresh gas was put in just last week. The filter from the tank to the pump was changed at the same time.

The main symptom I noticed, when I pulled off to the side of the road,  after it died the first time was that with the key ON the pump wasn't running. The fuel gauge on the FPR was also flatlined, but had occasional jumps up in pressure. The engine was also at operating temperature -- having just finished a 45 minute commute home in rush-hour traffic. 

Somehow, some way, when I started cranking, after a few attempts, the car was convinced to idle... and I limped home... It died two more times on the way. 

I suppose the next step would be to keep a multi-meter with me in the car to see if, the next time it dies, there's still voltage at the pump. I'm not eager to just "drive it until it dies again" though... God knows where I'm going to end up if I do that. 

What are some of your guys' immediate thoughts on this? Anything else that could be worth checking beyond all the stuff I just mentioned? Thanks in advance.

 

[siteunseen]

My first thought on the flat pressure gauge is your pump is going bad. If it runs all the time it seems to me you'd have more time/use on it causing it to wear out sooner. Just thinking out loud, good luck.

[Zed Head]

1 hour ago, KDMatt said:

1 - The fuel pump shutoff has been bypassed, so the pump will begin to run as soon as the key is switched "ON" and continue to run until the key has been switched "OFF"

The main symptom I noticed, when I pulled off to the side of the road,  after it died the first time was that with the key ON the pump wasn't running. The fuel gauge on the FPR was also flatlined, but had occasional jumps up in pressure. 

Somehow, some way, when I started cranking, after a few attempts, the car was convinced to idle... and I limped home... It died two more times on the way. 

What year car?  I've forgotten.  I'd assume that you can tell the pump isn't running by the lack of noise?

How did you bypass the shut off?  Seems like it must have been failing sporadically, maybe overheating, if it is the fuel pump power causing the problem.

If you're not sure it was actually the fuel pump power failing, it could be the ECU.  What you described is almost exactly what happened to me when my ECU failed.  I got close enough to run home and get an ECU that worked.  I was testing the one that failed.

[KDMatt]

Thanks for the quick replies!

@siteunseen -- the pump still only runs when the key is switched to "ON" so it shouldn't have abnormally high wear or use on it... Plus it's not very old. Thanks for the well-wishes.

@Zed Head -- car's a '76, and yes I can tell when the pump is running because it makes audible noise... In fact, my roommate has walked into the garage many times while I'm tinkering and asked what that "buzzing noise" is from the back of the car... in that respect, in addition to the flatlined FPR readout, it's easy to tell when the pump isn't running. 

A previous owner bypassed the shutoff by jumping a  couple of wires together on the fuel-relay harness... I couldn't tel you exactly which ones or how since I didn't do the work. It's been a fortuitous modification (since the aftermarket fuel-rail doesn't hold pressure like the OEM one does... it can be useful to give the system a few extra seconds to 'charge' before I try to start the car) so I haven't touched it. 

Easy way to tell if it's the fuel pump? It didn't feel hot to the touch... isn't the old trick a bit like a bad starter? Give it a few gentle taps with a wrench and if it starts moving again you know the bearings or something inside have seized?

Your comment on the ECU definitely made he gulp. I'm still battling some running issues with this thing and it could definitely point to the ECU as a smoking gun... I think I still need more evidence though... :/

Did the L28 ECU stay pretty much the same from 75 to 83? I know a few local ZX guys that might have an extra one from an S130 laying around. 

[Zed Head]

1 hour ago, KDMatt said:

A previous owner bypassed the shutoff by jumping a  couple of wires together on the fuel-relay harness... I couldn't tel you exactly which ones or how since I didn't do the work. It's been a fortuitous modification (since the aftermarket fuel-rail doesn't hold pressure like the OEM one does... it can be useful to give the system a few extra seconds to 'charge' before I try to start the car) so I haven't touched it. 

I'd focus on this.  Maybe he used wire nuts and they vibrated loose.  76 used the AFM contact switch to energize the pump relay.

The major downside to having the fuel pump run when the key is on is if the engine dies because a pressurized fuel line split, the pump will just keep pumping.  And it's not the rail losing pressure, it's probably the FPR.  Could be the pump though.

[siteunseen]

7 hours ago, Zed Head said:

 And it's not the rail losing pressure, it's probably the FPR.  Could be the pump though.

I thought about the check valve when I replied about having a weak pump but he has an aftermarket pump.  I guess the after market pumps have them too?

[Chickenman]

^ Yes they do...

Fuel pressure should be maintained by check valve in Fuel Pump. Losing pressure after sitting for 5 weeks could be a sign that there is a problem with the Fuel Pump.

My first thought would be to remove the small plastic pre-filter, cut it open and see if it is plugged with debris.

Second thought...  As always, check all your grounds and electrical connections thoroughly. Regular use of an Electrical contact cleaner is pretty much a SOP on these vintage cars.

Edited June 7, 2016 by Chickenman

[KDMatt]

Hey guys, thank you for the replies!

Going into the meat of this business with the fuel pump... my understanding of the L-Jetronic system in this car was that the pressure in the system was maintained by the FPR in the middle of the OEM rail... otherwise there is nothing to keep all the fuel from running back down the return line. I'm assuming the check-valve is what maintains pressure while the pump is powered and running? 

As I said before, right now I have an aftermarket FPR and aftermarket fuel-rail in the car. As far as I'm aware the design of the former is supposed to let it depressurize while the car is off. 

@Chickenman I'll double-check my connections, but this car hasn't seen a lot of action since the pump was replaced, so given my cursory glance I didn't see a whole lot of corrosion... No harm in pulling the contacts to look though I guess.

The new filter's only been on there a week and I didn't see any obvious signs of debris.

@Zed Head As far as the the wiring modifications go... the P/O used some of those goofy T-joints to do it and added a removable connection between the two ends... My guess is that he wanted to make a rudimentary kill-switch because when I pull the plugs loose from each other, the fuel pump no longer runs... in fact the symptoms are identical to what happened to me.

Now, I'm not going to say this is my "smoking gun," ... but the randomness of the "dying" as well as the sudden onset of it (and sudden complete recovery) certainly seem consistent with an electrical issue... and since this wire is near my clutching leg it's conceivable it got knocked loose enough to kill the pump.

Dunno, it's a working theory for now. I'll need to find some time to take the car out to see if I can duplicate the problem.

[Zed Head]

It's not's design aspect of the FPR, it's just a simple weakness or flaw.  But that is what many of the aftermarket adjustable FPR's do.  I used to have that problem with an Aeromotive.  I replaced it. with an adjustable Bosch FPR.

T'ing two wires at the replay could bypass the relay itself, or they might be bypassing the AFM switch.  

It could be that the T'ed wires to make the pump run all the time was an effort to fix the problem that you have now, but it didn't work.  You might just have a bad pump relay.  If you ID'ed the wires that were T'ed we could probably say why.

[KDMatt]

Just now, Zed Head said:

It's not's design aspect of the FPR, it's just a simple weakness or flaw.  But that is what many of the aftermarket adjustable FPR's do.  I used to have that problem with an Aeromotive.  I replaced it. with an adjustable Bosch FPR.

T'ing two wires at the replay could bypass the relay itself, or they might be bypassing the AFM switch.  

It could be that the T'ed wires to make the pump run all the time was an effort to fix the problem that you have now, but it didn't work.  You might just have a bad pump relay.  If you ID'ed the wires that were T'ed we could probably say why.

I just replaced the relay though. I never had a problem with it, even with the old one I had that had gotten a bit mangled. 

If I'm not mistaken, the wires that got bypassed/T-ed are the ones for the AFM shutoff switch. 

[Zed Head]

I asked earlier about year of car because the fuel pump relay is combined with the EFI relay on 75-77 cars.  Most people with 76 cars say that they replaced the EFI relay.  Or the EFI and pump relay.  I guess my point is "are you sure that it was the pump relay?"  It's about 1x1x2" and silver.

Power problems are actually fairly simple to diagnose.  If I had your sporadic problem, I'd wire a light in to the pump power circuit just to be sure the pump is actually getting power.  Don't overlook the connector next to the passenger seat.  It's under the carpet and could be one of those dirty connector areas.  Pump power runs through there, I think it's the last connector before the pump.  Good place for a light wired in.

[KDMatt]

2 hours ago, Zed Head said:

I asked earlier about year of car because the fuel pump relay is combined with the EFI relay on 75-77 cars.  Most people with 76 cars say that they replaced the EFI relay.  Or the EFI and pump relay.  I guess my point is "are you sure that it was the pump relay?"  It's about 1x1x2" and silver.

Power problems are actually fairly simple to diagnose.  If I had your sporadic problem, I'd wire a light in to the pump power circuit just to be sure the pump is actually getting power.  Don't overlook the connector next to the passenger seat.  It's under the carpet and could be one of those dirty connector areas.  Pump power runs through there, I think it's the last connector before the pump.  Good place for a light wired in.

Correct. That's the one I replaced. Small, silver, and under the driver's side panel, just above the ECU --- This thing:

 

The t'ed wire I'm talking about comes off of that. IIRC, on the '76, this relay controls the fuel pump as well as power to the EFI stuff, like the auxiliary air regulator. That is to say, with this thing removed, absolutely nothing happens when you turn the key to on or even try to click the starter. 

Could you elaborate on the "connector next to the passenger seat" though...?

I'm keeping a multimeter in my car right now so, if it happens again, I can jump out and see if the pump is getting power or not. 

I fiddled with the little T'ed in wire, made sure it was nice and snug, and took the car out for a little cruise... mixed driving... so far no issues. :/