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Common Sense + Critical Thinking
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They don't provide a spec for while it's running, but those poppet valves won't even open under about 45psi.

With that fast of a leakdown, you have a leak somewhere. If you don't have any visible leaks it's most likely under the intake plenum. Most likely the regulator, and you will see the pass side washed clean with fuel once you remove the plenum. Be careful which regulator you buy, IIRC Dorman was a little too large and you would have to trim the mounting tabs just a little bit. Maybe they have fixed that by now, don't know.

Upgrading to MPFI is also an option, esp if you are planning on keeping the van for a long time. Astro-Safari-Info - Fuel System
While you are in there, you really should consider replacing the LIM, considering that there was coolant in your oil. It causes problems way before it's even visible in the oil.

As far as the low pressure, I wouldn't blame the pump just yet. Did yours come with a replacement connector that you had to splice in? Wired correctly? Check the ground at the fuel pump connector, where it connects to the body. I would do a voltage drop test for both the power and the ground at that connector, with the pump running by carefully backprobing the connector.
 

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Let me start with the fact that I am not a transmission expert. I barely know the basics of how an automatic trans functions.

This was an intermittent problem with the van when I first bought it, but it has now transcended to a full time issue.

The van drives normally when I putter around town and on the highway - but when I floor it (regardless of the how fast I am going), the van will downshift and rev up, but I won't really gain any speed.

I've added about 1/2 a quart of Lucas transmission stop leak after reading about similar issues with the 4L60E, but I haven't noticed any improvement.

Could this be a sign of my TCC solenoid going bad? How should I even begin to diagnose? I have a scan tool, but I'm not sure that it reads any transmission codes. I have no check engine light, no codes present, and all monitors set.

Thanks
Max
Hi Max....I ran into a similar issue, loss of power under WOT. I was thinking fuel too, but I took it to a local shop for diagnosis. Recently I had replaced the distributor assembly as the gear was worn and ignition timing was sloppy as a result. I was getting code for random misfire under WOT. Fuel pressure seemed okay around 50 psi.

Mine ended up being plugged catalytic converters. The shop pulled the O2 sensors out and screwed in a pressure gage. Under WOT it was blowing the gage off the scale....it simply couldn't breathe. I had them replace the catalytic Y pipe assembly as a result and it has been good ever since. Worth a look.
 

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Watch his video, his fuel pressure is dropping like a rock.
I did go through that too. My original fuel pump quit. Replaced with aftermarket, which only lasted a month. Fuel pressure dropping badly under any acceleration. Replaced with a genuine GM unit, has been good ever since.

Mine has been in commercial service for 12 years, they are a great truck! Really not much has gone wrong with it considering how much I have put it through.
 

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Discussion Starter · #25 ·
The only reason I am sceptical of the fuel pump and not the regulator is because I don't have any of the common regulator issues. I don't have extended crank times even when the van has been sitting for a few days. I don't smell fuel - van is not running rich.

From what I gather, these are just the regular vacuum diaphragm fuel pressure regulators which in my experience either work or they don't, they usually don't exhibit intermittent issues.

I may rip into the plenum and see if it's been washed by fuel - I have new LIM gaskets and I need to get them installed, might as well get a definitive view on what's causing the issue.
 

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I'm not saying 100% it is or isn't the pump, could be the power supply to the pump, connector(s), grounds, etc. I forget what years were prone to melting the fuel pump connector, some come with a new one, that is why I asked.

Do I think the leakdown is an issue with your fuel pump, nope, I think it's more than one problem.

You can definitively find the leak by running the pump up to pressure and clamping off the supply and return lines. If it holds then it's rear of those points, if if still leaks it has to be in the plenum.
 

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Discussion Starter · #27 ·
My new pump did come with a new connector and pigtail, but my old one looked fine so I kept the wiring intact. I will try clamping off the pump today when I get home.
 

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Discussion Starter · #28 ·
So I finally had some time to dig into the van. I got the plenum off and the spider out, and now I am confused.

From pics of the different spider assemblies, it looks like I have the later style spider (recessed poppets). They look just like the late style poppets shown on the motorman website.

The pressure regulator does not have a vacuum barb on it. I am heading to AutoZone to figure out which regulator I need.

The pressure regulator screen was completely clogged up with debris when I removed it. It is clean now, I think that may have been my problem.

Hopefully someone is online to help clear my confusion.
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You don’t have poppets. You have the MFI spider, which is 6 individual injectors out on stalks.

I’m not sure how the regulator could have gotten clogged with debris if the fuel filter was installed and intact, unless someone really screwed up somehow.
 

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Discussion Starter · #30 ·
You don’t have poppets. You have the MFI spider, which is 6 individual injectors out on stalks.

I’m not sure how the regulator could have gotten clogged with debris if the fuel filter was installed and intact, unless someone really screwed up somehow.
Thanks Leeann. So that means that I have the later style MFI already already installed. Neat! Saves me a few bucks.

This van has a questionable history (used to be a drug mule), so someone really screwing up isn't out of the question.
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The original fuel tank had a large built in compartment for extra storage, which unfortunately cut fuel capacity down to about 1.5 gallons. I have no doubt that there is all kinds of things wrong with the fuel delivery system.
 

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Discussion Starter · #32 ·
Welp, everything is back together and the van is running and driving. The problem is still present - I have not thrown my gauge on it yet to check fuel pressure when it acts up, but I believe it is likely the (cheap) fuel pump.

The van does run a lot better after the new intake manifold gaskets and regulator, but still loses power on WOT.
 

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Discussion Starter · #34 ·
Negative, I will try to crawl underneath it today and check voltage drop.
 
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