Before November I had zero knowledge of basic maintenance on my blazer besides oils changes. Blazer wouldn't start so had it towed to a shop, they said my fuel injectors needed replaced and lower intake gaskets needed to be replaced too, I said go for it of course. Got it back, had rough starts, 2 weeks later, fuel pump goes out. Shop wanted almost 600. I did it myself. Ever since have had rough starts - not all the time but 80%.




I did the leakdown tests. At the service port it started out with ~60 psi, 10 minutes later dropped to 48, 30 min later dropped to 44. Made sure all connections were good and no fuel leaking, roughly same numbers.
Did the test at the fuel filter - while pump was running, psi was over 100 psi. quickly tapered down to around 85. after 10 minutes, was at 77. So there probably is a leak in the plenum. So what is the next step to take? I feel pretty confident replacing the fuel injectors if need be or if I take it back to the shop that put the injectors in, what do you say? Hey, did some diagnostic tests, pretty sure you screwed up? Ha. Just kidding but really, thoughts? Thanks.


I've also replaced the dist rotor and cap with ac delco, didn't help the rough start issue.

 

Fuel pump max output at 100psi is fine. Leakdown to 77psi is fine. Regulated pressure at 60psi is borderline low, and leakdown to 44psi is excessive. Any leakdown, (at the service port) below fuel pump leakdown, (77psi) means the leakdown problem is in the plenum. To determine if the leakdown is being caused by the regulator, it needs to be isolated from the tank immediately after pressurizing the system. This requires a shut off valve to be installed in the fuel return line. To determine if the leakdown is being caused by the injectors, an injector balance test is necessary using a capable scanner.

We know that regulated pressure is low, which indicates a problem with the regulator. It may also be the cause of the excessive leakdown. It can be replaced seperatly from the injectors, however, if an injector is leaking, it's cheaper to replace the entire assembly with an upgraded one, which includes the regulator.

 

Thanks for responding captain! So something like this? Mobile: Max Power 1/4" Fuel Shut-Off Valve 339134: Advance Auto Parts

Got a trip to make this weekend. Not going to have time to diagnose until next week unfortunately.

 

Needs to be far more substantial than the nylon one due to the higher pressure.
The return line is 5/16", you'll need to fabricate something like this:

 

Looks like the dorman #800-121 you Listed in the leak down thread along with the fuel line. I'll look around for the other pieces to do that.

Does it matter where in the return line it needs to be?

 

Very similar to the adapter, but this one goes in the return line. It is connected inline so when the valve is open, you can activate the fuel pump for a few seconds to purge the air through, then deactivate the pump and close the valve simultaneously. If it holds pressure, the regulator needs to be replaced. If pressure drops, you'll need to do the injector balance test, and most likely replace the injector assembly.

 

Called around to shops today to see if anyone could do a fuel injector balance test. Only one shop said they could and they wanted to charge 100 bucks. Another said he would kill one injector at a time to test them for 50 per injector. Everyone else said they could not. Really don't want to spend that money to see if it's leaking, might as well buy the spider assembly and do it myself.

I think what I'm going to do is take it back to the shop that put the injectors in and see if they'll fix it, if not, I'll do the return line test.

 

If you have to hire someone to do the tests, it will drive the overall cost well above that of replacing the assembly yourself. That's what I was getting at in post #2:


"We know that regulated pressure is low, which indicates a problem with the regulator. It may also be the cause of the excessive leakdown. It can be replaced seperatly from the injectors, however, if an injector is leaking, it's cheaper to replace the entire assembly with an upgraded one, which includes the regulator."

The Delphi part # is FJ10565. Amazon, Ebay, and Rock Auto have good prices, but it pays to shop around.

 

Thanks for all your advice captain, I really appreciate you helping me out, I'm still a big noob with all this car stuff. Just kinda sucks that I had a shop put in my injectors and having problems not even 4 months (really 200 miles) later. To be honest, I'm a little nervous trying the return line adapter just because I don't want to screw anything up.


Once you recommended doing an injector balance test, I searched Google and the tools to do the test are pretty expensive at least for a decent one - so I called around, still too high to even consider it. Is there another way to do the balance test? Is there a chance that a visual inspection could help?

 

The shop should warranty the injector assembly, take it back to them. Now that you know how it works, you can explain what the problem is. Regulated pressure is too low, and leakdown in the plenum is excessive. If they have questions, have them log in on the forum and read the thread


The shut off valve in the return line can be tricky. If the test isn't done exactly right, it will destroy the regulator, guaranteed.