MAP issues (P0108)

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someotherguy

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For the sake of anybody searching in the future, best I can find is that the original cap screws (GM part #10475922) can be replaced with an oversize screw (GM part #10457666). I would assume that just makes the problem bigger at some point. If the distributor holes stripped with small bolts, they're going to strip with bigger bolts. I see that as a temporary fix, though it might be several years worth of temporary, until the next time you need to unscrew the cap.

The Dorman part looks promising, but damn...somebody is making a fortune stamping those out in China, and getting 20 bucks a pop. And if I need it today, $30+ at my local parts stores. I've also seen it suggested to put 2 small studs in the distributor, with various combinations of Loctite or epoxy (JB Weld?), and never have to deal with it again. I can get a couple little studs at ACE hardware for probably 27 cents.

For now....zip ties to the rescue
Stick with the zip ties. They'll last forever, or until the next time you need to pull the cap and just cut 'em off. Oversize screws will just end up breaking the tabs off the distributor body which is plastic, and already cracked.

Richard
 

mudpie

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A few weeks ago I replaced a dead Delphi fuel pump with a new Delphi pump. I checked the fuel pressure today and I'm getting this at idle. Granted, it idles rough, and it dies after 8 or 10 seconds, but I thought these trucks needed at least 55 psi to run at all. At least that's what I recall reading in just about every fuel pump thread I've seen.
I didn't put a new filter on it this time, but I did when I replaced the pump in 2017. Since then I've only put maybe 10k miles on it, so I'd guess the filter isn't clogged.
 

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stutaeng

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A few weeks ago I replaced a dead Delphi fuel pump with a new Delphi pump. I checked the fuel pressure today and I'm getting this at idle. Granted, it idles rough, and it dies after 8 or 10 seconds, but I thought these trucks needed at least 55 psi to run at all. At least that's what I recall reading in just about every fuel pump thread I've seen.
I didn't put a new filter on it this time, but I did when I replaced the pump in 2017. Since then I've only put maybe 10k miles on it, so I'd guess the filter isn't clogged.
Yikes! No bueno amigo!

You either truly have low pressure or your regulator is dumping all of the fuel into the intake. Or leaky injector. That pressure needs to fixed before you do anything else. If you are dumping enough fuel into a cylinder you can hydrolock it and bend a connection rod.

I think with little inspection mirror or boroscope you can look into the intake to check out regulator.
 

alpinecrick

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Yikes! No bueno amigo!

You either truly have low pressure or your regulator is dumping all of the fuel into the intake. Or leaky injector. That pressure needs to fixed before you do anything else. If you are dumping enough fuel into a cylinder you can hydrolock it and bend a connection rod.

I think with little inspection mirror or boroscope you can look into the intake to check out regulator.

I wonder how much gunk has been accumulating upstream including in the gas tank for the 5 year old fuel filter to catch. Low fuel pressure may be a hint.
 

mudpie

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I'm generally pretty careful about fuel stuff. When I pulled the pump I blew all the dirt off the top, scrubbed it with a small brush, blew it off again, then took the pump out. Inside the tank was very clean.
Just put a filter in it, just because they're only ten bucks, and cleaned all the threads before taking it apart. New filter didn't make a difference, and there's not much to see inside the old one, but what I can see looks spotless.

Somebody refresh my memory...
Fuel pressure regulator is under the intake manifold, right? I'm pretty sure I replaced that and the intake gasket when I updated to the newer style spider, probably 6 years ago.

I'm pulling the bed to look at the pump.
 

454cid

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I'm generally pretty careful about fuel stuff. When I pulled the pump I blew all the dirt off the top, scrubbed it with a small brush, blew it off again, then took the pump out. Inside the tank was very clean.
Just put a filter in it, just because they're only ten bucks, and cleaned all the threads before taking it apart. New filter didn't make a difference, and there's not much to see inside the old one, but what I can see looks spotless.

Somebody refresh my memory...
Fuel pressure regulator is under the intake manifold, right? I'm pretty sure I replaced that and the intake gasket when I updated to the newer style spider, probably 6 years ago.

I'm pulling the bed to look at the pump.

You might check voltage drop to verify its not wiring. Both power and ground.
 

stutaeng

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Yes, FPR is under the plenum.

Is that the instantaneous fuel pressure? If so, try priming it a few times to see if pressure increases, even slightly. In that case, I'd lean more towards fuel pump.

You said that's at idle. What is the pressure with engine off, key on? And does it hold pressure?

Or does it to drop to that pressure? FPR, although a large leak wouldn't allow much pressure to build up.

You have to determine if pump is not building pressure or if there's an issue where fuel pressure is going somewhere. Possible leaks are injectors dumping fuel into cylinder(s), FPR leaking into intake or check valve in fuel pump. First two are very common and last one I always have heard about being possible, but never seen it happen.
 
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someotherguy

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A few weeks ago I replaced a dead Delphi fuel pump with a new Delphi pump. I checked the fuel pressure today and I'm getting this at idle. Granted, it idles rough, and it dies after 8 or 10 seconds, but I thought these trucks needed at least 55 psi to run at all. At least that's what I recall reading in just about every fuel pump thread I've seen.
I didn't put a new filter on it this time, but I did when I replaced the pump in 2017. Since then I've only put maybe 10k miles on it, so I'd guess the filter isn't clogged.
You said one reply further down that you've upgraded to the new style spider. The absolute minimum 55psi or so (general number) is what is required for the old style, the poppet setup, to operate. Lower pressure simply won't force the poppet valves open to spray fuel. With the new style spider you have actual individual injectors which many have reported normal operating pressure slightly below the published spec (52psi or so) and no issues. Your considerably lower number is very suspect, but may not be enough to keep the truck from running. The new spider not depending on the poppet valves makes it *somewhat* similar to the 7.4 setup, and I've had one of those run (poorly, but would run) at only 30psi.

As mentioned by others I'd say you're on the right path chasing the fuel pressure issue. If indeed your gauge is reliable and accurate, that low pressure is a huge red flag.

Richard
 
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