Edit: Fuel pressure related issues

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Tavi

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92, 454 TBI, 4L80e. New plugs wires, cap, rotor, ICM and coil.

Yesterday, I made a 150 mile trip up to Colorado Springs towing my enclosed 16’. Truck ran fine all the way there. On the way back I started having some engine troubles. I had a very similar occurrence about a year ago, last time I drove it to the springs. But nothing since.

Here is as accurate as I can conclude what is happening:
Pulls fine going up hill. All gauges reading in normal. As I crest hills and let off the throttle (engine braking, 2500-2700 RPM). As I get back into the throttle, the throttle acts as a big vacuum leak (Lowers the RPM). Engine will maintain its RPM and slow with the vehicle speed, I am unable to get any power. The vehicle will slow until the engine ultimately dies.

Once dead. It will turn over but not start. If I wait another five minutes or so. It will start, with full power.

Today it ran fine for the first 45 minuets. Then died out, regardless of conditions. But would restart almost immediately. Now it won’t make it 50 feet before dying, but idles fine.
 
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GL1500

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Obviously you need to stop going to the Springs! in lieu of that, were the components listed replaced prior to the trip last year, or after it gave you trouble then but before this trip?

Have you changed the fuel filter. Could be just enough blockage to starve the engine, especially after running under heavy load for a while. Might also check fuel pump relay and related connections. Just throwing some ideas.

Best wishes
 

Tavi

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The parts were changed just before both trips. ICM took a dump a few weeks prior to the first trip.

Fuel filter is probably overdue. It, the new ICM and the fuel pump were my primary suspects. But the unique conditions required had me curious.

I forgot to mention, if I kept on the throttle going over a hill. It would not create the symptoms. On if I lifted.

I ordered a new fuel filter. Since it probably needs one anyway. But I’ll keep you posted.
 

DerekTheGreat

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Hmm yeah, what's that fuel pressure doing I wonder? I think after awhile of engine braking the fuel pump is shut off by the ECM, seems like when you get on it after that the fuel pump doesn't kick back on and so she dies. That or the pump is on the way out. Vat it zeems like anyway.
 

Tavi

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I’m very curious too. But no fuel pressure gauge. But during the no fire condition. There is no fuel coming from the injectors.

With the truck on the side of the road, at a slant to the right. It would fire up fine. With the brake on and in gear, I was unable to replicate the condition. Once I pulled onto the road, and it hit second gear, it would bog and die.

I got a strap and the wife towed it home with the suburban. I let it idle for ease of steering and braking. If I tried to apply throttle. It would bog, but if I let it idle just fine for about ten minutes otherwise. So I’m pretty positive at this point it is fuel pressure related.
 

Tavi

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Update:
Changed out the fuel filter. Didn’t hear the fuel pump running. Jumped the relay and heard the pump. Plugged the relay back and heard it running.

After a few tries the engine fired up. But was stumbling. Weak injector cone. More than a stream. Less than a nice solid cone.

It acted like this regularly in the past, but would clear up after at least 30 seconds. I guess it just took the pump a minute to get on it’s feet.

I’m assuming the pump has been dying a slow death. But with less than 20 hours of use in the last three years. It took a while to die.

I see a lot of people recommending oil pressure switch. I assume it is an on off switch type deal. I can hear my pump running. But could it be running weak?

Unless someone else has some recommendations I’m going after the pump next.

I updated the name of the thread to better resemble what I have narrowed it down to.
 
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Tavi

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Update:
I had the ICM tested at autozone. The parts guy said it failed. Did a warranty exchange through rock auto. And ordered a Bosch fuel pump at the same time. Replaced the ICM with no change. Pulled the bed and replaced the pump. After about 5 seconds of cranking engine fired up and put her back to work.

I’m not sure the ICM was tested correctly. As most parts store guys are less than knowledgeable. But I went ahead and replaced it anyway.
 
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