here read this for lift pump test post #er 4

Running rough or missing

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Here some info for LP

To check lift pressure use a test gauge on sale often at Harbor Freight or at most auto part stores if you can't wait;
connected to the filter manager drain tee, connect a long hose to the gage & run to inside of the cab, take care to not pinch off the hose and dead head the reading. After careful routing close the hood and go for a drive.

At idle healthy lift pump should supply 5+ psi, when at cruise speed it should maintain 3-4 psi, on hard acceleration pressure may dip to 1-2 psi but should recover back to 3-4 cruise pressure, if pressure drops below 1 psi pump is weak or OPS is acting up and one or other needs replacing.

ok see the link didn't come on last post

https://www.dieselbombers.com/chevy-...tml#post842937

 

Okay.

This morning after going for breakfast I came home and did the T-Handle fuel check.

After only a turn, I got a very steady and even flow of fuel out of the handle stem and the fuel line.

I tightened the t-handle down and the engine still idled flawlessly.

Also, I found where the loss of power is most noticible.

47MPH, 1650-1700 RPM.

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Ok so I know i keep adding more and more instances when this is happening, but i figure the more examples I give the more someone might know what the hell is going on.

Today I took the truck down the highway, call it 10-15 miles. Zero issue at 65+ MPH all the power in the world, no studdering.

Im about to get off the highway, I let off the accelerator to coast down to a sane speed to attempt to take the exit. As soon as I depress the accelrator again (to gain a little speed because it was an uphill ramp) there she goes, studdering and hiccuping again! it only seems to be under slight throttle application.

I also noticed that when I went to get back on the highway, after idling for 30 sec at a STOP SIGN, I hammered it, and she seemed to cough before it actually got going....


WEIRDNESS!!!!!!!!!!!!

 

Another update:

Today i started the truck up, and needed to go somewhere in a hurry, but the truck was up to temp. Well, the thing was an absolute DOG. Truck wouldnt get out of its own way! I mean my 6.2IDI could SMOKE my truck at the moment.

What the hell gives, the damn thing has basically new everything minus pump and injectors. Idles beautiful, highway she does just fine! AND on top of it I am getting great flow out of the fuel system.

Only thing I can think of, and I cant understand how, is that she's getting air in the fuel.....and even then HOW. The only non-stock replacement is the fuel filter (which my buddy said is a style the doesnt use the stock "ring?"

Someone, anyone, please help me out!

 

Go back read post 11

you maybe getting fuel out T-Valve but going down the and stepping on the fuel you not getting fuel pressure the lift pump may be weak you won't know intill put gauge on it

 

Okay Folks.

Last night I did the popular OPS Relay Mod.

I used a trailer wiring harness (for the 4 connected wires).

Came out well, and I left myself and extra wire incase I ever wanted to power the relay directly from the battery and not the orange wire.

I also picked up a fuel pressure gauge from Autozone, and did the fuel pressure test using the tee-handle and a long hose.

After taking the air out of the line, I then let it idle.....between 5-7PSI constant. I took it for a ride, and upon heavy throttle (floored) it only dropped to 3.5-4 PSI. Cruising it was at 5-6PSI. I tried and tried to make it change and it never dipped below 3PSI. Also, when the truck shutters/hiccups/losses power the gauge does not change.

One note: on the new PMD Heat-Sync there is a black wire separate from the others that is crimped onto an existing wire running down somewhere under the IP. I assume it is grounded thru this.

So I bought a 1993 6.5 LP in hopes that it WAS the LP that was bad.....looks like I'll save $77.99 Now but still have my issue.

 

here few pics of the OS filter we talk about on the phone

 

well after a lengthy conversation on the phone, we narrowed it down to either PMD, IP, or LP.

Today, I switched out the LP from my 1999 style to a 1993 style, and wouldnt you know it, problem solved.

I residual pressure while idling is 9-10PSI and under HARD accel. is 5-6.

Also, when gently raising the RPM from idle to 2500, the truck would get the hiccups around 1550-1650 before......now it is smooth as silk.

 

Glad see it fix