92 454SS Hard Start stalls fuel pump runs continuously

[92Red454SS]

I am the original owner of a 40K mile 1992 454SS truck. All original with no modifications.

The engine cranks excessively and once it starts it runs for about 20 seconds then stalls (sometimes). It will do this once or twice on restart. Additionally when it stalls it seems like it looses spark as it does not surge or try to keep running. The stall condition is intermittent, but it always cranks excessively to get it to start. No check engine light.

Naturally when I open the air cleaner to view the fuel flow from the injectors it doesn't stall.

In the past when turning the key to the on position the fuel pump could run for 2-3 seconds. Now it runs continuously for 20 seconds. I removed the pump relay and checked it for proper operation and it appears fine. Fuel pump was changed about 10 years ago.


I have read posts about possible faults being the ignition control module, coil, temperature sending unit, oil pressure sender, ground at thermostat housing, fuel pump relay. Any thoughts?

 

[PlayingWithTBI]

The engine cranks excessively and once it starts it runs for about 20 seconds then stalls.

Check your fuel pressure 1st, it should be 11 - 13 PSI (GM spec is 9-13) when the fuel pump is running.

Also wondering if during normal operation it is suppose to spray fuel during the 2-3 second fuel pump activation or just prime the lines? I don't see any spray of fuel prior to cranking the engine.

Yes, it just primes the pressure regulator and lines, the injectors should only spray when the engine is turning over otherwise, it would flood the engine.

In the past when turning the key to the on position the fuel pump could run for 2-3 seconds. Now it runs continuously.

On the 5.7 (I'm pretty sure the 7.4 too) there's an oil pressure switch on the back of the engine that will bypass the fuel pump relay and turn on the fuel pump. If it is shorted out or stuck closed it may run continuously.

 

[92Red454SS]

I did some additional diagnostics today: With the key in the on position I can hear a high tone for two seconds followed by a low tone which continues for 20 seconds coming from the fuel pump. I'm assuming the pump primes and gets dragged down causing the lower tone. Upon cranking, fuel begins to spray from the injectors and the engine starts. If I disconnect only the oil pressure switch the engine will start. If I disconnect only the FP relay the engine will start. In each case only after excessive cranking. If I disconnect the relay and oil pressure switch it will not start (parallel circuit). I'm guessing my FP relay and oil pressure switch are good.

I don't know much about the FP control module, but read something about it should run 20 seconds? I thought I should only hear the pump run for two seconds?

The oil pressure switch on the L19 454 motor is located on the lower left front corner of the block where the oil pan and timing cover meet. Easy to reach and disconnect from up top.

I am going to make an adapter block to fit in place of the filter with a gauge to check the fuel pressure. Perhaps I have a pressure or regulator problem?

Can't induce the stall condition. It is intermittent. I'm leaning toward the ignition control module on that one?

YouTube video:

xc_hide_links_from_guests_guests_error_hide_media

 

[someotherguy]

The few second prime is normal. Trucks that run it for 20-30 seconds are equipped with the "hot fuel module" which are on -some- trucks originally delivered to very hot climates. Your truck changing behavior from short to seemingly long prime is more indicative of a problem than a feature. I would suspect the oil pressure switch is defective. I may have mis-read but I don't see the diagnostic step of what the pump does if you turn the key on (not start) and see how long the pump runs with the oil pressure switch disconnected?

You don't need to build anything to test fuel pressure. There are Tee fittings made that can go inline with the filter, or up behind the TBI for a more permanent installation. Actron used to sell a gauge kit that came with it - and they also list that Tee for sale separately for about $8. It may be a little tricky to find one easily, but don't be fooled into paying significantly more from other sources selling the same part. I've seen that Tee offered at $30 and more.

This is the whole gauge kit, the particular model of which has been discontinued - but you should be able to find a similar setup. If you can't, I have a couple of these kits still new-in-package on my shelf and would be willing to sell one.

You must be registered for see images attach

Here's the Tee installed behind the TBI. I did this on my '94 because it was lowered and I didn't want to have to jack it up just to get the gauge attached by the filter. This can require loosening the fuel line clamp attached down by the transmission.. I also highly recommend installing a cap to protect the valve from dirt. A spare A/C fitting cap works just fine.

You must be registered for see images attach

Richard

 

[PlayingWithTBI]

I got mine from RVMorse.com

You must be registered for see images attach

 

[92Red454SS]

I’ll try to PM you to see about helping you clear one off your shelve..

 

[someotherguy]

I got mine from RVMorse.com

You must be registered for see images attach

That RV Morse part seems good if you want a permanent install as that liquid-filled(?) gauge should hopefully stand up to long-term vibration and heat under the hood.

For a test gauge that you can move from vehicle to vehicle easily, the Actron (or similar competing) kit is the way to go, IMO. Though obviously if you want to move it from TBI to TBI you either can't leave the adapter mounted, or you wanna buy extra adapters.

Richard

 

[PlayingWithTBI]

That RV Morse part seems good if you want a permanent install as that liquid-filled(?) gauge should hopefully stand up to long-term vibration and heat under the hood.

No, it's not liquid filled.

For a test gauge that you can move from vehicle to vehicle easily, the Actron (or similar competing) kit is the way to go, IMO

Agreed, I'm just showing a different option...

 

[someotherguy]

No, it's not liquid filled.


Agreed, I'm just showing a different option...

Hmm, well it's probably fine - I don't think those guys would sell junk. They're definitely the go-to for bored-out TBI units instead of getting them from the dudes re-selling RV's work at a higher price!

Richard

 

[PlayingWithTBI]

Hmm, well it's probably fine - I don't think those guys would sell junk.

IIRC - the liquid filled gauge will be inaccurate with the heat generated by the engine but, again my CRS (Can't Remember ****) syndrome is kicking in, lol