2002 7.3 hpop starts and dies out

808gmac · February 7, 2015

I have a 7.3 that starts and dies out, what can cause hpop reservoir to go dry? If I check res. before starting it its filled, after it starts and runs for a few seconds it stalls out and hpop res is dry, after that its a long crank before it restarts, after I get it running it runs great. Could the low oil press pump be bad and. not able to keep up with supplying enough oil to hpop? Wouldn't that cause other drivability problems though? Could hpop drain out internally back to crankcase ?

Bruce Amacker · February 7, 2015

Common pattern failure on 7.3s, just like you thought it's the LPOP. Pull it out and measure between the teeth with a feeler gauge, the pump will look fine visually and be 3x the spec on clearance.

Good Luck!

:grin:

808gmac · February 7, 2015

Spec. .028"-.032" between outer rotor and housing, where do you find spec between inner and outer rotor? 001"- 003" for pump to housing. I will need to disassemble and check clearance's. Is there other tests that can be done before disassembly?

Thanks for such a quick response

Keith Browning · February 7, 2015

.003"-.004"

Posted Image

808gmac · February 7, 2015

Thanks for the info,could hpop,or injectors cause this concern?

Bruce Amacker · February 8, 2015

No, it's just old age, mileage, and maybe lack of maintenance that causes the reservoir to be full on startup and stall 15 seconds later. The oil in the galleys is actually draining back past the gear teeth from the pump outlet (to the galleys) to the pickup tube. With .003" there's not much drainback but the ones I've had were .012-.015" which lets the galleys drain out. You start the engine, it runs on the reservoir, the LPOP lost it's prime and is struggling to get primed again, and the engine stalls. Enough cranking and the pump primes and all is well until the next cold soak.

If the front cover is worn by the LPOP the engine has to come out, so prep the guy for that.

If the reservoir empties out while parked several days it can be the HPOP allowing it to drain out.

Nice pic, Keef, where'd ya get that? :grin:

808gmac · February 8, 2015

could pickup tube be cracked and sucking air or would that cause other concerns like oil aeration and lack of power? wasn't there some kind of test where you overfill crankcase and jack up rear of vehicle?

Bruce Amacker · February 8, 2015

Yes, but if your only concern is the reservoir going empty 15 seconds after a cold startup my money's on the pump. Cracked pickup tubes cause aeration which has a completely different set of complaints, like wildly swinging ICP on a warm engine and stalling.

:grin:

cbriggs · February 15, 2015

I seem to remember something about a drainback / check valve in the oilfilter housing? I don't know much about 7.3s though....

808gmac · February 16, 2015

Able to start working on it today , will check lpop, hope to find clearance excessive so I can sleep tonight

Bruce Amacker · February 17, 2015

I seem to remember something about a drainback / check valve in the oilfilter housing? I don't know much about 7.3s though....

That was the OF bypass valve which was staked in place on the '94-5 engines and would commonly fall out, giving the engine unfiltered oil forever after that. It went to a snapring retaining it in '96ish. I have pics I'll load up when I get time.

It would give no symptom other than trash getting in places it shouldn't and premature wear. I'm sure many of them ran years like that.

:rolleyes:

808gmac · March 3, 2015

Well Bruce,

Sorry it took so long to reply but got parts and put truck back together, YOU THE MAN! Thank you so much for all your help, the lpop clearance was the culprit.