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Car Forum / Chevrolet / Chevrolet Trucks / October 2006

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93 c1500 4.3L needs ether to start hot

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News Skimmer - 01 Oct 2006 21:39 GMT
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
69SScamaro - 06 Oct 2006 03:44 GMT
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)

> This one is strange to me. Any help would be appreciated.
>
[quoted text clipped - 56 lines]
>
> Thanks, Skimmer
News Skimmer - 07 Oct 2006 20:58 GMT
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

> 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
[quoted text clipped - 73 lines]
>>
>> Thanks, Skimmer
69SScamaro - 08 Oct 2006 13:52 GMT
> Thanks 69'er
>
[quoted text clipped - 92 lines]
>>>
>>> Thanks, 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.
 
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