88 L98 not starting when warm

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Jan 27, 2026 | 01:24 PM

#21

Tunedperformancedotorg

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From: Cotopaxi, Colorado

Does fp raise with return line pinched ?

Jan 27, 2026 | 03:46 PM

#22

Lettuceman

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From: Bergen county NJ

Non start when engine is warm...

Quote:

Originally Posted by snackstick

This is a engine swap using a !988 L98 engine and a Painless standalone wiring harness. I have had different threads on this forum and have received good help. The truck is starting and running but not great and will not restart when warm or hot. My question is when I unplug the MAF It speeds up but the engine does not sto

p. There is no check engine light except when I unplug the MAF. Are there a way to check the sensor to make sure it's bad before purchasing a new one.

check the wire that powes the starter. Mechanic found a splint in the wire tat separated when warm.ran an independent wire to the starter, works fine now.

Jan 27, 2026 | 04:28 PM

#23

Tunedperformancedotorg

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From: Cotopaxi, Colorado

Quote:

Originally Posted by Lettuceman

check the wire that powes the starter. Mechanic found a splint in the wire tat separated when warm.ran an independent wire to the starter, works fine now.

this is a painless 60102 same basic wiring as a 1227165 in 86-89. The power wire off the starter is for SAM of the ecm and backup power to OPS. Since it starts and runs the splice shouldn’t be a issue and isn’t causing lower fuel pressure.

Jan 28, 2026 | 11:28 AM

#24

snackstick

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No it didn't change after the return line was pinched, also I purchased a adjustable fuel pressure regulator top and after following the instructions of adjusting I ended up running the adjusting screw all the way down and it didn't change a thing. still 40 psi

Last edited by snackstick; Jan 28, 2026 at 11:33 AM.

Jan 28, 2026 | 11:44 AM

#25

Tunedperformancedotorg

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From: Cotopaxi, Colorado

If pressure doesn’t rise with return pinched you have leaking injectors or a weak pump. I’d guess the pump is weak. Just a guess

Jan 28, 2026 | 12:57 PM

#26

snackstick

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OK I will change the fuel pump again. thanks

Jan 28, 2026 | 01:47 PM

#27

Tunedperformancedotorg

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From: Cotopaxi, Colorado

Intank or inline ?

Jan 28, 2026 | 08:19 PM

#28

snackstick

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intank

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Jan 28, 2026 | 09:34 PM

#29

IHBD

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Quote:

Originally Posted by snackstick

intank

What size is the O.D. of the outlet nipple on the fuel pump? 5/16" or 3/8"?

If it is 3/8", you have a "low pressure" TBI pump. TBI pumps will make 40-ish psi, but they struggle. The 5/16" outlet is the TPI pump.

Jan 28, 2026 | 09:53 PM

#30

Tunedperformancedotorg

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From: Cotopaxi, Colorado

Quote:

Originally Posted by snackstick

intank

I’m not up on good quality intake pumps lately. Racetronix and aeromotive and Walbro through summit racing might be the best choices.

Jan 30, 2026 | 10:28 AM

#31

snackstick

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switch on and the 2 second fuel pump run, does it just prime the fuel rail and injectors or does it also put fuel in the cylinders?

Jan 30, 2026 | 03:48 PM

#32

Tunedperformancedotorg

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From: Cotopaxi, Colorado

Quote:

Originally Posted by snackstick

switch on and the 2 second fuel pump run, does it just prime the fuel rail and injectors or does it also put fuel in the cylinders?

it primes the rail no injector pulse during prime. If the pressure doesn’t hold after the prime you could have leaking injectors or a bad pump check valve .

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Feb 3, 2026 | 01:47 PM

#33

snackstick

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I just ran a resistance check on my 9th injector and it was 3.3. even cold it takes three 2 sec switch on to start. and won't start when warm. plus bleeds down pretty quick. I assume that the ninth injector can bleed down just like the other 8.
My questions are
Can you block off the ninth injector without reprogramming the ECM
Does anyone know of a service that rebuilds the ninth injector? I have found used ones but you never know what you get.

Feb 3, 2026 | 01:54 PM

#34

Tunedperformancedotorg

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From: Cotopaxi, Colorado

https://www.hawksmotorsports.com/198...ery=Cold+start

cold starts may suffer but going to $6e tune is a option.

Feb 3, 2026 | 02:02 PM

#35

snackstick

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I have already seen the kit but before buying I want to know does the 9th injector give feed back to the ECM

Feb 3, 2026 | 02:08 PM

#36

Tunedperformancedotorg

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From: Cotopaxi, Colorado

Quote:

Originally Posted by snackstick

I have already seen the kit but before buying I want to know does the 9th injector give feed back to the ECM

feedback ? The csi works by the starter giving the timer switch power while cranking. Is the timer is closed the ninth injector then sprays cranking only.

Feb 3, 2026 | 02:19 PM

#37

snackstick

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Ok thank you

Feb 3, 2026 | 03:14 PM

#38

snackstick

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I was just informed from another source that the cold start injector resistance is suppose to run from 3 to 5 ohms, Does anyone know if that Is true?

Feb 3, 2026 | 04:15 PM

#39

Tunedperformancedotorg

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From: Cotopaxi, Colorado

Quote:

Originally Posted by snackstick

if the csi is leaking it doesn’t matter it’s ohms . You might just delete it . And other csi you find will be 38 years old or older.

Feb 3, 2026 | 04:20 PM

#40

Tunedperformancedotorg

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From: Cotopaxi, Colorado

https://www.thirdgen.org/forums/tpi/...-troubles.html

this shows timer and csi ohms

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