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93 c1500 4.3L needs ether to start hot

This one is strange to me. Any help would be appreciated.

Symptoms first...

+4.3 tbi starts fine when cold. When new it started faster than you could let off the key, takes about two seconds now...even if I wait a second for the two second prime +Turn it right off, starts right up +Drive it until hot and turn it off....cranks but no run +Spray in some ether....sputters then runs...never dies

Some history

+I drive this truck only a few K per year to haul trash, lumber etc. +About 5K miles ago, reported EGR intermittently...I ignored it because it was so rare and it passed emissions test. +Last month, fuel pump went deader than dead with no notice. Checked numerous ways....dead. Wouldn't spin even when connected to 12V +I replaced the pump with a new pump and didn't mess with EGR until happy with pump. +After a month, this hot start problem occurred and EGR code 32 more frequent. Yesterday I replaced EGR (dead with vacuum pump) and solenoid although okay and cleared memory. +Today, still having the problem. Now I haven't driven many miles to re-build fuel trims since the repair and clearing the memory ...but I'd expect it to start hot.

Some tests results.....

+Fuel pump runs 2 seconds after ignition on...pulls 2 amps, takes 10 second rest to reset (all as designed) +Fuel pump runs when cranking....no fuel from injectors when engine hot +I've even directly powered the fuel pump through the fuse connection (not the OBD test connection) with a 10A fused ammeter before and during cranking. The engine cranks and cranks with no fuel from the injectors until I spray a tad bit of ether, then magically the injectors turn on and it runs, never dies. Performs full strength when running implying good fuel flow and pressure.

I don't think this is a fuel pump system related problem. Something is not turning on the injectors during the cranking cycle until somehow it detects the engine is running (i.e. ignition pulses with the switch in run, not start?).

I'm not sure where the oil pressure switch fits into this, but I can achieve high oil pressure during cranking hot so that should clear. Shouldn't matter to the pump, because I've directly powered it...but it might matter to the PCM if it is looking for oil pressure to turn on the modules. I'll go back and check my diagrams for this feature.

There are no MIL codes now that EGR is fixed.

Any help would be appreciated.

Thanks, Skimmer

Reply to
News Skimmer
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Second try....is the group stumped????....you too, Snoman?

Symptoms first...

+4.3 tbi starts fine when cold. When new it started faster than you could let off the key, takes about two seconds now...even if I wait a second for the two second prime +Turn it right off, starts right up +Drive it until hot and turn it off....cranks but no run +Spray in some ether....sputters then runs...never dies

Some history

+I drive this truck only a few K per year to haul trash, lumber etc. +About 5K miles ago, reported EGR intermittently...I ignored it because it was so rare and it passed emissions test. +Last month, fuel pump went deader than dead with no notice. Checked numerous ways....dead. Wouldn't spin even when connected to 12V +I replaced the pump with a new pump and didn't mess with EGR until happy with pump. +After a month, this hot start problem occurred and EGR code 32 more frequent. Yesterday I replaced EGR (dead with vacuum pump) and solenoid although okay and cleared memory. +Today, still having the problem. Now I haven't driven many miles to re-build fuel trims since the repair and clearing the memory ...but I'd expect it to start hot.

Some tests results.....

+Fuel pump runs 2 seconds after ignition on...pulls 2 amps, takes 10 second rest to reset (all as designed) +Fuel pump runs when cranking....no fuel from injectors when engine hot +I've even directly powered the fuel pump through the fuse connection (not the OBD test connection) with a 10A fused ammeter before and during cranking. The engine cranks and cranks with no fuel from the injectors until I spray a tad bit of ether, then magically the injectors turn on and it runs, never dies. Performs full strength when running implying good fuel flow and pressure.

I don't think this is a fuel pump system related problem. Something is not turning on the injectors during the cranking cycle until somehow it detects the engine is running (i.e. ignition pulses with the switch in run, not start?).

I'm not sure where the oil pressure switch fits into this, but I can achieve high oil pressure during cranking hot so that should clear. Shouldn't matter to the pump, because I've directly powered it...but it might matter to the PCM if it is looking for oil pressure to turn on the modules. I'll go back and check my diagrams for this feature.

There are no MIL codes now that EGR is fixed.

Any help would be appreciated.

Thanks, Skimmer

Reply to
News Skimmer

Check the pressure from the fuel pump. Ours the pump just started getting weak and had a tough time giving a spray. It would only put out around 5 psi. We misted gas into the tb and sometimes it would start running on it's own after a while. We thought the same thing with the oil pressure switch and the ignition pulse, but you can remove the oil pressure switch on a good running one and it will still run. I think it checks for both op and ignition pulse and as long as it has one it'll run. Check the pressure... I wish we would have before swapping out distributor, oil pressure switch... (from another one of our trucks so it didn't cost anything)

Reply to
69SScamaro

Thanks 69'er

My pump is brand new. (The other died without warning.) But of course new doesn't always mean good.

I agree on the oil pressure switch.

My next step is to build a NOID light to be sure the injectors are working or not during cranking. I don't see any fuel spray when cranking but it could just be that the wife is involved while I'm looking down the barrels. Things are hard to figure out when she is involved.

Can anyone post the resistor and LED values or RadShack part numbers to gen up a NOID light? Also whether the two are in series or parallel?

skimmer

Reply to
News Skimmer

They are separate. One is injector A drive the other B drive. Our truck had a fuel pump that was only months old when it died... The oil pressure switch is a back up in case the relay takes a crap. It is wired in parallel with the relay and when it gets pressure it sends 12V directly to the fuse for the pump. It is a fail safe way that they do it so your not relying on just a relay or just the oil pressure. As far as the NOID not sure what values to use... Did you check to see if your pump is running or not ? no pump no fuel and the injectors won't spray with low pressure. Ours wouldn't spray at the 5 psi our pump was delivering.

Reply to
69SScamaro

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