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Confusing PMD/LP conditions

R

Rodd

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Location
Antelope, CA
I had some of these in my "fish on" thread but I don't want to get things convoluted. Here is what is happening and what has been done. It is bucking, cutting out and stalling the last few weeks.

I replaced the ops day before yesterday because the LP tested good when I jumped it. I was able to fill 1/2 cup in 2-3 seconds. The truck had been bucking and giving pmd failing conditions. I replaced 2 pmd's. Luckily I have 3 good ones. Same results, Bucking, stalling, etc.

Today I drove 20 miles out to the airport and it started cutting out above 60 mph. At 55 mph it was fine. As I got closer to home I thought I would push it a little to see if I noticed anything. From a stop it would start to cut out/buck at 2500 RPMs. Then it ran like crap the rest of the way home. I pulled into my driveway and opened the t valve and it died. LP is 2 weeks old and the OPS was just replaced. The OPS has been in my glove box for 8 months so it could have failed just by getting knocked around in there. I need to go jump the pump to see if it is still working. If it is then it points to the ops again.

Here is everything that has been done to my truck in the past year or so.

Ops - 2 days ago
LP - 2 weeks ago
Fuel Filter - 2 weeks ago
New battery - 5 days ago
Oil change - 1 1/2 months ago
rebuilt IP - Nov 2008
Rebuilt injectors (dieselpro) - July 2008
New FSU - July 2008
186k miles

Since it stalls when I open the t valve that point to the LP or ops. One thing that I noticed is that when I opened up the bleeder on top of the filter fuel doesn't come out of the black spout it comes out between the black spout and the filter top. I don't think that would cause my symptoms.
 
I just went out and before jumping the pump I wanted to see what would happen if I opened the t valve and turn the ignition on. I got fuel. Why would it die when I open the t valve w/ it running and not pass any fuel then let it sit for 15 minutes and open the t turn the ign to on and I get fuel. Whats up?
 
Rodd said:
I just went out and before jumping the pump I wanted to see what would happen if I opened the t valve and turn the ignition on. I got fuel. Why would it die when I open the t valve w/ it running and not pass any fuel then let it sit for 15 minutes and open the t turn the ign to on and I get fuel. Whats up?
Click to expand...

Hi Rodd. Your OPS controls power to the LP while the engine is running - when you have oil pressure, you get power and therefore fuel.

The ECM controls power to the LP while in start or wait-to-start mode... because obviously you have no oil pressure, right?

SUMMARY:

--With the engine off and key on, you get power from ECM - not from OPS.

-- With the engine running, you get power from OPS - not from ECM.

The symptoms point to a failed or defective OPS. Test power at the LP with the engine idling.

Jim
 
vail426 said:
How much pressure are you getting?
Click to expand...
I knew someone was going to ask this question. I don't have anything to check it with. I have been seeing all the posts about fuel pressure and thinking I need to get a gauge but haven't done anything with it. I recall seeing a post from Tim that said if you have good pressure you should be able to fill a pint in about 30 seconds. At 1/2 cup in 2 - 3 seconds I am faster than that. The only think is if I am loosing fuel pressure while driving that is a problem.
 
JiFaire said:
Hi Rodd. Your OPS controls power to the LP while the engine is running - when you have oil pressure, you get power and therefore fuel.

The ECM controls power to the LP while in start or wait-to-start mode... because obviously you have no oil pressure, right?

SUMMARY:

--With the engine off and key on, you get power from ECM - not from OPS.

-- With the engine running, you get power from OPS - not from ECM.

The symptoms point to a failed or defective OPS. Test power at the LP with the engine idling.

Jim
Click to expand...

Thanks Jim! This is kind of what I thought. How do I test power at the LP w/ truck running? Unplug connector and stick my probes in?
 
Yeah - the truck shouldn't stall just by unplugging the LP. Pull the plug and test for power.
 
JiFaire said:
Yeah - the truck shouldn't stall just by unplugging the LP. Pull the plug and test for power.
Click to expand...

The first time I unplugged the pump I couldn't get my leads connected fast enough before it died. The 2nd time I got the leads connected a few seconds before it stalled. I did have power to the pump. So where now?
 
When you had your LP off, did you get a good flow of fuel out of the line? With an IP as fresh as yours is I would think it would be able to suck enough fuel to run at idle. I am thinking you may have a restriction somewhere.
 
Yep - good test, Rodd. If pulling the plug on your LP causes a stall, then you have a restriction somewhere (or an air leak) that is preventing your IP from pulling fuel at idle.

Start back by the LP... if you're getting good fuel flow there, then the sock is OK.

Work your way forward... you are definitely starving somewhere.
 
I just took the truck on another test drive out to my parents 15 miles away mostly on back roads and every time I got it above 50 it started cutting out. When I got to my parents I ran some wire from the battery to the LP and guess what the problem was still there. It actually got worse like it was fuel starved. It actually putted along at 15 mph and it was flat. I shut her down for about 5 minutes and drove 4 miles at about 45 mph then it slowed to 15 for the last 1/2 mile. I am thinking like you guys there may be an obstruction
 
Forget about the OPS right now.

Drive it with the LP jump directly to 12V source to see if you are still cutting out.
If you still cutting out and you can start, there is something else is wrong.

When you jump the LP, start it, it should start (if LP is good), then measure the voltage at the OPS to LP connector.
 
JMJNet said:
Forget about the OPS right now.

Drive it with the LP jump directly to 12V source to see if you are still cutting out.
If you still cutting out and you can start, there is something else is wrong.

When you jump the LP, start it, it should start (if LP is good), then measure the voltage at the OPS to LP connector.
Click to expand...

You may have missed it in one of my previous posts. I did jump the LP and had the same probs. I am looking for obstructions.
 
Get a cheap fuel pressure gauge at harbor freight or elsewhere

Blow air into tanik and see if problem persists, with fuel cap off. Remove LP inlet line and blow air in there.

Even try running with fuel cap off.


I suspect something amiss in your tank... (not that you want to hear that).
 
How full is your fuel tank?

Pressure gauge is the most definitive if you have LP issue.
By the way, sometimes, new something may not always be good because it can be defective.

Is your new OPS ACDelco?

I recall that you have been having trouble with the fuel tank also, hence the new FSU.

Can the new FSU defective?

It is puzzling to me for all this trouble when everything is new.

Recently, I experience this with my bro's nissan's new belt. Put the old one back, squealing was gone.
So new belt was bad.
 
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