Doonze

1999 Suburban 5.7, when I first got this truck, about 20k or so ago, it had an issue where it would sometimes not start(Sometimes like 3x a month?). It would crank, but would never catch. You could hold down the key for forever, and it would just crank and crank.

At the time, I figured out if you just let off the key as soon as it wouldn't start, and tried 2 more times, on the third time, it would ALWAYS start fine. Never dies when running and has never cut out on me. I recently hauled a car 150 miles through the mountains and it didn't miss a beat. Is always fine once started.

Now, the last 3k miles or so, it's been getting much worse. It's 2-3x a week it does this. And the 3 times trick no longer applies. Sometimes it takes 20-30 tries to get it to start. Maybe more. The way it's acting I can tell it's fuel.

So, no security light. It comes on like normal during the lamp test, but doesn't stay on after that. I HAVE seen the light while running like 2-3 times in that last 20k miles, but other then the light being on, nothing else weird. And it would start fine right after, cause I tested. It ACTS security related, but the light not lighting tells me it's not, right?

Tried 3 fuel pump relays. Same problems. As luck would have it, it's never done it when I haven't had to be somewhere (like work) so I've never been able to trouble shoot while it's not starting. But I can verify the Fuel Pump relay clicks when the key is turned to on, and it has power I verified with a MM.

So, first question, is there something in the ignition switch that JUST energizes the fuel pump?? Or is the "on" position all that it takes? I know everything else works like it's supposed to in ON. Would a bad switch or bad connection aside from security cause this issue? The fact for years just cycling the switch on and off fixed it seems to indicate switch to me.

Second question, could the fuel pump itself "seize" when it gets shut off, and it's taking multiple cycles of sending power to it to get it to start spinning??? Like I said above, once it's spinning it never stops. I'm just wondering if it it's like my lawn tractor that takes a couple tries to get the starter to get moving.

I don't want to just throw parts at it, FP isn't the cheapest or easiest part to replace. So I'm looking for experiences and opinions.

Thanks.

(BTW, I have searched this, most post with my symptoms says security. But the security light not being on makes me think it's something else.)

Hrpchr

My vote is fuel pump.


One of the ways to test the fuel pump is with an oscilloscope, because it will show the pulsations of the windings of the pump itself. Just because the fuel pump relay makes, and there is some sound from the pump (if you can hear it), it doesn't mean its pumping fuel forward.


Sometimes one or more of the windings is bad in the pump and it all depends on where the pump stops the last time used. Sometimes it stops on a 'bad' segment, and only vibrates when you go to "Run". You cycling it through multiple start attempts probably bumps it around until it gets to a good segment to start from.


Think of it like a starter pinion and ring gear, where the ring gear has some missing teeth. If the engine stops at the missing teeth, it won't spin the motor at startup. Rock the vehicle in gear, move good teeth to the starter, and it starts right away. The segments in the fuel pump behave similarly -- if the pump stops on a bad segment, it doesn't start, it just vibrates.


The 1999-2002 Suburbans use two different fuel pumps, a two-pin (two wires) and a four-pin (four wires), and it depends on either the VIN or visual inspection to know which is which. I have "heard" that GM replaced the two-pin pumps with four-pin pumps to alleviate that bad-segment problem. Evidently the four-pin uses two sets of wires for two different starting segments to overcome a single bad segment causing intermittent no-start problems. I think there are eight fuel pump segments (windings) in both pumps.

Doonze

That sounds like it could be it! I was really trying to avoid doing the FP. Since it works, and these are so famous for... not working.

What's the latest thoughts on what one to get? I know about 90% seem to fail right away. What the best one to get?

Hrpchr

The symptom of a bad segment or two is usually persistent, meaning that a quality shop can check it even when it's working properly. The waveform of bad segments appear differently on an o-scope even whilst it's running.

Additionally, having a fuel pressure gauge (about $25) can show the pressure at the fuel rail on the engine in a no-start situation. It would at least confirm if the pump is pumping.

Remember, the fuel pump runs at the "Run" position of ignition switch, so the engine does Not have to already be running to check it.

Doonze

The stealership would not be one of those quality shops. The guys was like "What the heck are you talking about? Windings??? I've never heard this before." Then told me it would be $800 to do the FP.

Really, I just called them to see how long they would warranty the work. 1yr/12k. WTH??? He was like, yeah, we used to do lifetime, but not these days! That's what I was calling for, bad as the pumps are on these, I wanted like 5 years at least. For lifetime I would have dropped $800...

But no way to that! I'm still trying to find someone who can test mine. But in the meantime I'll try and figure out what pump I'll get...