intermittent fuel pump failure at startup only

[mikesarge]

Here's a fun one:

TL DR: Is intermittent "no pump" at start up a symptom of a failing fuel pump?

Car is running EFI, so no CIS components present.

Every once in a while, usually once the car is warmed up, but occasionally on a random cold start, the fuel pump will not prime, and the car won't start. So far, after giving it a few minutes, it's started to work every time. It gives me pause about taking the car very far from home though.

I've removed the aftermarket alarm system, verified the wiring is good (continuity where it's supposed to be), and replaced the relay (and even bypassed it using a jumper in place of a relay), and the problems persist very intermittently.

Is this a dying fuel pump? unfortunately the fuel pump is a PITA to get to, so when it happens, the process of taking off my (bent) belly pan, and running 12v direct to the pump would likely be inconclusive at best.

The pump happily makes 40psi throughout the rev range for me as soon as it's running, as verified on the dyno.

Also, this happened before I ran the fuel pump relay reversal wiring to use my megasquirt signal to trigger the fuel pump, so i've isolated that as a factor, I think.

I gotta imagine the answer here is "check for voltage at the pump when it happens..." which basically means I gotta wait until it gets worse I guess.

I do feel like I've narrowed it down to the pump itself here given the relay jumper, but basically wanting confirmation that this is possible, before I start spending the time removing/replacing that stupid belly pan over and over again

Anyway, I welcome anyone's thoughts on this

[chrisbruck]

My 3.2 Carrera was doing something very similar late last year and it was the fuel pump failing. I did the same checks you did and swapped out the DME relay. Pretty much narrowed it down to the fuel pump. Only would happen at startup and never while running. Intermittent and didn't matter if hot or cold. The tell tale sign for me was the last time it wouldn't start I jacked it up, bypassed the DME relay so the pump was constantly energized, banged on the pump with a light hammer and sure enough the pump started humming away and fired right up immediately after that. Mine also happened to be leaking so replacing it was a no brainer.

Next time yours doesn't want to start, tap on the pump and see what happens. May help and show its ready to be replaced.

[mikesarge]

Great idea to tap on it- thanks

[dfhtrhjn]

I replace all my fuel pumps once over the lifetime of my cars. If you ever take the time to cut one in half, you'll be surprised by how worn the internals are even when they produce the correct fuel pressure. The updated Bosch part is $140, quiet like a mouse, and in my opinion worth the piece of mind.

[MichaelSJackson]

I had a warm start problem. May or may not be related, but easy to check.

New fuel pump, filter and relay and lots of testing this and that got me nowhere. Finally punted and took it in.

The FP relay wasn't seated well enough in its socket. The mechanic showed me how each prong is sheathed by thin metal that is folded over the tip of the prong. If you look, you can see a cross-hair on the tip. He took a thin knife and pried the cross hairs open just a little to get it to fit a little more snug. My problem was solved and it never came back.

In my case, the loose connection was causing the socket to heat up and make it even looser. Sometimes too loose to restart when warm.

Michael J.
'78 SC w/Bitz

[mikesarge]

Alright, here's how I'm (hopefully) going to close this one out. Went out this morning, turned the key, no pump. Hit the skid plate with a hammer, pump goes. (shout out to chrisbruck)

So, I swapped the pump with a URO brand pump I had bought last week after the rough diagnosis above. Swapped it out, hit the key, we've got pump. It's loud, but it pumped right up to 40psi per my FPR gauge in the engine compartment. Car runs. Time will tell if this actually addressed the problem I guess, but I like the preliminary results. If I had to do it again, I'd probably buy the bosch one for the noise level, but I'm happy I can hear the pump- better than silence and no pump!

The old pump was marked "germany" but no brand. Maybe it was original? no idea. No check valve in it- just a regular ol' banjo bolt. The new one came with a check valve but it was weird looking- a long banjo bolt with no head, and a plastic end in it. Incomplete hardware so I had to pull that and go with the prior banjo bolt. new crush washers from my stash.

Otherwise, for the archives- this job is easy. Remove belly pan. Pinch the feed hose, get a catch pan and un-do the banjo bolt. it'll spew a little fuel. Undo the electrical connections. Loosen the clamp on the feed line. Unstick the feed line from the pump. Undo the clamp holding the pump in place. Swap the pump. I like to go feed-end first, just in case the clamp gives out. Do up the electrical connections. Do up the banjo. Double check it's all tight. Test it. If it works, and doesn't leak, put the pan back on.

The hardest part of the job was fixing the gummed up threads on the front skid plate bolts. Someone had an off-road excursion in this thing at some point and took out the bottom threads at a bit of an angle. It wasn't a problem when I did the front sway bar a few months ago, but today it was. I had to chase the threads with a die, then clean up the nut with a tap. Oh well, all done

[PeteKz]

Mike, I'm a little late to the thread, but you got good advice to tap the pump to see if that gets it running. It did, and you replaced it, so problem fixed. Where is that URO pump made? China, or somewhere else?

NOTE: It doesn't matter what fuel pump you put back in, as long as you can physically adapt it to the lines, AND it delivers the required pressure and volume. I say this because a lot of people think you must replace with the same pump as original. You don't. Even though a CIS pump is designed to deliver higher pressures for the CIS than most EFI pulsed injection systems use, the fuel pressure regulator in your EFI system will dump the excess pressure and fuel back to the tank. The Bosch and Bosch-licensed pumps in cars worldwide only have a few differences. Bigger pumps deliver more volume for larger engines, and the adaptors to fit certain cars are different (thus different part numbers), but the basic guts and operation of them are the same.

I had an old 1975 VW bus at one time that needed a fuel pump (I got tired of laying down and reaching under it to whack the fuel pump every time), and I adapted a Carter or something from Summit Racing because it was cheap. It worked for several years until I sold it, and if that bus is still on the road, it probably still has that pump in it!

[chrisbruck]

Glad you got it sorted. I opted to have a shop do mine as I couldn't tell exactly where my leak was and they redid a couple of the old tunnel lines. My new pump is noticeably more noisy too. Don't recall what brand they used. Hope it lasts but so far so good.

[mikesarge]

Thanks to PeteKz and Chris for the follow-up.

One more piece here, as I'm looking at things. I think I know the answer, and it's "it doesn't matter," but thought i'd consult the brain trust before I do a 2.5 hour drive in bad weather to a HPDE.

My old pump had an integrated check valve. The new pump does not, so unless I buy a cap nut, I am just running a banjo bolt with no check valve at all. Does this present any problem beyond a potentially longer startup time? The car starts fine, and I don't mind a little extra cranking. I'm running EFI, so the system is only seeing 40psi anymore, for what it's worth that way too. Other than that, is there any potential downside here? most importantly, is there any potential to cause damage?

[PeteKz]

It may be harder to start warm, without the check valve. If that's a problem, then install one. Like the pump, it does a generic function. You could install one in-line with the fuel hose, if that was easier.

[mikesarge]

got it- sort of what I thought. If anything, I'll just buy the cap nut and put it in the right place, that's easy enough.

thanks!