I appreciate all the posts that have helped me so far on this Blazer. I try to find answers from other's posts, and often do. Also try to contribute here and there. But sometimes a problem is just unique. I'll try to be succinct:


1999 Blazer LT 4WD
Previous owner ran engine dry of oil, so I purchased it 6 months ago, tossed a 4.3 from a 98 Jimmy with maybe 80,000 miles on the crate engine.
No codes stored, though we did have a EVAP P0442 code awhile back.
Poor mileage (12.5 mpg)
We have only put a few hundred miles on it. It has good power and throttle response.
Usually starts on first crank, but RPMs seem "lazy" for a few seconds
Occasional it takes several minutes to idle correctly. But it does eventually idle nicely.
New spark plugs, wires, O2 sensors, cleaned MAF, CAT is clean.
Dizzy gear is not worn badly, though it is not perfect.
Cam/Knock retard set close to zero plus/minus 1 degree. Seems to hold within 1 degree.
As part of engine swap 6 months ago, I installed a used MPFI spider from a salvage yard.

I decided to check fuel pressure at the port. 57 psi and it is not holding. Drops fast to 30 psi or less in just a few minutes.

Pressure right after filter is 75 psi and holds above 55 psi for 15 minutes or more.

Removed upper intake. No apparent fuel leaks/washdown, but there have not been many miles on this engine since spider swap and lower intake gasket replacement which included cleaning carbon off the lower intake (intake gasket was not leaking, just preventative).

Installed new fuel pressure regulator. Leakdown still occurs. Suspected a bad FPR out of the box, I purchased another one. Similar leakdown still occurs. I have 2 new FPRs and 2 old FPRs. Same result with all of them. Even same result trying the old CPI spider. Some FPRs may hold a little better than others, but none are even close to specs (55 psi for 10 minutes).

I am certain that no poppets or poppet tubes are leaking, as I have the poppets removed from their intake ports and lying on a dry towel between them and the intake. Same with the spider body and FPR - no fuel is dripping from them. Just to make sure, I plugged the return line fitting near the rear of the block. While this may not have done my old FPR any favors, it held 58 psi for over 10 minutes. This again tells me my fuel pump check valve is OK. It also tells me that my spider is not leaking externally. Additionally, it tells me I have no leaks in the fuel lines between the pump and spider.

Only things I can think of is that I have an internal leak in the spider between the supply and return lines, or I have 4 bad FPRs. I have confirmed that there are only 2 O-rings on the FPR (1 large, 1 small), and have made sure I installed the new ones that came with the new FPRs.

I plan to check fuel pump pressure at filter one more time. BTW, I see and feel no leaks in any fittings, such as pressure port, FP gauge, etc.

Any ideas? I hate to purchase a new spider, but I am thinking that is the next move.

 

"Pressure right after filter is 75 psi and holds above 55 psi for 15 minutes or more."

Although 75psi with the engine off and the pump running is low, it is within spec, (73psi to 108psi). Holding above 55psi means there are no leaks in the tank. Bottom line, your pump receives a D-.


"I decided to check fuel pressure at the port. 57 psi and it is not holding. Drops fast to 30 psi or less in just a few minutes."

With the engine off and the pump running, 57psi is too low, (needs to be 60psi to 66psi). It must remain above 55psi for at least 10 minutes after the pump shuts off. Regulated pressure and leakdown both receive an F.


"I plugged the return line fitting near the rear of the block. While this may not have done my old FPR any favors, it held 58 psi for over 10 minutes."

The fuel pressure regulator valve plate is leaking internally. This will prevent the fuel pressure from achieving the regulated pressure it is set for, and cause the excessive leakdown that you're experiencing.

In the future, keep in mind that if the regulator is exposed to ~75psi or more, (restricting the return line) the chances are real good it will rupture the diaphragm in the regulator. Your "saving grace" this time was probably due to your pump maximum output pressure being so low

 

Thanks for the quick reply.


I can't argue with the "D-" for the pump, and a "F" for the regulator. I just have a hard time believing that 2 new FPRs in a row were bad out of the box. I may try a few more times before I work up the nerve to spend more money.


Will keep trying and post the results.


-Steinke

 

Next time you have the regulator out, check the black plastic tube inside the fuel metering body. Make sure there are no cracks, and that the O rings are sealing.


After removing #13 through #18







The tube, (not shown) is inside the fuel metering body.

 

That's a great diagram.

I checked the plastic tube in the body. It is not cracked and holds air pressure. Also fits snugly into o-ring inside the body. I think I have ruled out any leaks in the black plastic tube.

I rechecked the fuel pump pressure by removing the fuel line from the spider and blocking the supply outlet with a hose, clamps, and hose plug. Pressure at the test port is 85 psi with pump running. Holds above 55 psi for about 20 minutes. So I just don't think it's a pump problem. That's three passing tests for the pump pressure and check valve. It has never failed a test.

I reinstalled the spider and tried both new FPRs. Pressure dropped off for each FPR, but at different rates (both still quickly). So I'm going to try yet a 3rd new regulator. I have tried ACDelco and BWD so far. May order a Delphi this time.

Will update with results.

 

This link might be helpful: https://blazerforum.com/forum/2nd-ge...eakdown-88305/

 

Received the new Delphi FPR today. I installed it and pressure still bleeds down. I try different FPRs and get different leak down rates, but none are acceptable. I'm certain I have the o-rings in right.

This is insane. Fuel pump delivers 85 psi to filter (measured at "rail" or schrader valve) and holds pressure. 2 used spiders and 5 FPRs (2 used and 3 new) max out at 55 psi and won't hold pressure.

I guess I have no choice but to buy a new spider. It's frustrating.

 

Ok I tried a brand new fuel spider that of course came with a new FPR. Same results. My next plan is to replace the fuel pump. Maybe the check valve will seal at 85 psi with the "deadhead" condition (plugged supply line at filter), but the check valve will not hold at the 60psi regulated pressure allows by the FPR.

 

Follow the steps exactly as written in the link in post #6. You will need to build the fuel filter adapter to get accurate results. The parts necessary are listed at the end of the article. Post all 4 readings and we will analyze them, and diagnose the problem.


EDIT: If the pressure regulator is exposed to ~75psi or greater, it can rupture the diaphragm and cause an internal, and or external, fuel leak. If you're seeing 85psi at the service port by the distributor, you're probably rupturing the diaphragm in the regulator.

 

My method was to disconnect the fuel line from the spider. Than hoseclamp a tight-fitting hose to the supply line "gooseneck". Plug the end of the hose with a bolt and hoseclamp. Then I can use the fuel test port to check pressure without ruining my FPR. That gives me 85 psi and it holds above 55 psi for over 20 minutes. That's why I have tried 6 different FPRs and 2 spiders. Still can't find it.