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Old 02-18-2018, 09:11 AM   #1
kimallman
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98 Tahoe runs 1 second, goes dead

Could this be the oil sending unit ? Decided to replace it but it’s a bear to get to. Then I read on here that the oil sending unit has bypass circuitry that no longer kills the fuel pump if oil pressure drops too low, as in some earlier GM models. It has an Excalibur alarm system on it, but it seems if this was the problem it wouldn’t crank to begin with. Any ideas ?
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Old 02-18-2018, 11:17 AM   #2
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Re: 98 Tahoe runs 1 second, goes dead

Welcome Aboard!

If you suspect a fuel pressure problem, jumper the FP relay so it runs constantly, then start the engine. There is little sense in digging into the oil pressure switch and wiring if the diagnosis doesn't point you in that direction.
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Old 02-18-2018, 05:31 PM   #3
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Re: 98 Tahoe runs 1 second, goes dead

I misread the post and pointed to a starter issue, Blue Bowtie is on point.
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Old 02-19-2018, 01:13 AM   #4
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Re: 98 Tahoe runs 1 second, goes dead

Run 1 second and die sounds to me like the security system- not reading Passlock II resistance properly. What is security light doing? It should come on then go out after start.
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Old 02-19-2018, 06:45 AM   #5
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Re: 98 Tahoe runs 1 second, goes dead

BR is getting ahead of me. I was trying to get you to eliminate one item at a time.

Of course, he's correct as well. The security system will run the injectors for only about 2-3 seconds if the key transponder doesn't read. I just wanted to see if the fuel pump ran or not, taking us another step down the diagnostic path in one direction or another.

Incidentally, the auxiliary oil pressure switch does not act as a fuel pump cutoff, and it never did on domestic GM vehicles - All the way back to the 1976 Cadillacs. I believe Ford tried that for a while. It was one of their "better ideas."
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Old 02-20-2018, 12:40 AM   #6
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Re: 98 Tahoe runs 1 second, goes dead

Just as a side note, my 1977 Vega had the FP wired through the oil pressure switch OEM- Never had to check the oil, the 270 degree exit ramp would tell me if I was low. Engine would cut out on long curve- If I straightened up, it would cut back in again. Oil light would come on at same time.....
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'94 Astro- 370k miles
'94 Firebird Formula- 5.7L 180k miles- gone-
'92 Chevy Lumina Van 3.8L 264k
'86 GMC S-15 - 2.8L 154k
'87 Buick Park Ave . 187k
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'77 Chevy Vega- 2.5L 175k miles gone but not forgotten
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Old 02-20-2018, 07:40 AM   #7
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Re: 98 Tahoe runs 1 second, goes dead

Vega? I'd almost forgotten about them. I guess that counted as a GM vehicle, and they did have some unique features. Good education.
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