I was wondering what the PSI/ time is normal leak down for a 92 CPI unit.

I found this posted in the archives: https://blazerforum.com/forum/archiv...p/t-45941.html

A fuel system that drops more than 34 kPa (5 psi ) in 10 minutes has a leak in one or more of the following areas:

o The fuel pump check valve
o The fuel pump flex pipe
o The valve or valve seat within the fuel pressure regulator
o The fuel injectors
o A fuel pipe

I bought a fuel line tester today and my leak rate was 8lbs in approx. 3mins. Known replaced parts: CPI unit, plenum fuel lines. The prior owner said he replaced the fuel pump. So what should I check next?

Ok here's what I hate about the internet, anyone can be an expert.....found this at another site: "On 1992 through 1994 pressure must remain above 50psi for 3 to 5 minutes after the pump shuts off."

So, now I have 2 different references, my PSI held at 50 after 3 mins so which is right?

 

>5psi drop in 10 minutes applies to all of the CPI & SCFI engines. So if yours started at 55psi and dropped to 50psi after only 3 minutes, you have a leak that needs to be addressed. You can find the leak by connecting the fuel pressure gauge to the fuel supply line at the fuel pump directly, disconnecting the line to the engine. If the leak is still present, then you have a bad check valve in the fuel pump. If it isn't, then the leak is inside the engine ('nut kit', spider body, or FPR).

 

Here's the symptoms:

fuel pump on pressure @ 58lbs
I have a leak down rate of 1lbs per minute
fuel pressure fluctuates during rev (-10lbs swing)
bad fuel consumption
normal driving seems fine
combustion smells a little rich
no gas smell
no gas in oil

Known replaced parts:
CPI unit
nut kit
fuel filter
fuel pump

My thoughts are of frustration now. I have a pretty good understanding of this CPI system now and there are only a few things that could cause a swing in the fuel pressure while under load. The fuel pump, how do you check the pump to simulate a load condition. I can check the static pressure at the pump but the pump seems to be delivering 58lbs at key on. The regulator could be faulty, but with less than 500 miles on the re-man CPI unit that would really **** me off. Same would **** me off if there is a poppet valve sticking. I know this is a new injector unit so trying to run a cleaner to free a poppet be a bad idea? Another question I have is if the pump is leaking pressure would that mean the gas would stay in the tank and not be lost? Thinking on that line if there is a pressure drop at the pump then the main injector would give a poor spray and lead to a degraded spray at the poppets causing poor gas mileage?

 

You unhook the fuel filter and put the pressure gauge on there on that connection. You should be getting better than 58 pounds out of that pump, I think it should be up around 90. Checking it at the schrader valve is not the pump pressure, its the pressure allowed by the FPR cause it lets excess presssure bypass it and return to the tank. When you hook up to the fuel line direct, it should get up to about 90 and the pump should turn off and it not leak down - I think this is how you would do the test Swart suggested.

The fuel in the oil has to build up over time. Mine took a few days to get a couple litres overfull and its a very bad leak. I betcha my 3 and 4 plugs are black and wont spark too.

How do you know that the CPI unit is a known replaced part? Did you do it? The PO could have just told you that after he seen how expensive they are....

Seriously though, from history of what Ive read... Just take 10 minutes to open up your upper intake, turn the key foward, and LOOK with you eyes for the small fuel spray or dripping. It might look like quite a task, but its not. You need a 10MM socket and driver, and a multi bit screwdriver, and disconnect the various cables and plugs. And dont forget to unhook your coil power plug as well. Spark and fuel are a bad mix, so take the possibility of spark outta it. This is a problem that we have pretty much all had. And as for opinions around the internet, you chose the right place for the know its alls of blazers.

 

I know the CPI unit is new because I put that in. I know the nut kits was recently replaced because the PO gave my the tray with the old parts in it. I also know the fuel pump was replaced twice, because the PO didn't know that leaking nut kit was causing the fuel pump to fail from constant running. I also replaced the fuel filter. So as it stands, i was going to work on the trans / trans mount tomorrow but I am determined to resolve this fuel issue so I am going to test the fuel pump and pull the plenum tomorrow. The quality of low end parts has been an issue on this truck before. I am not going to be surprised if the re-man spider is failing.

 

Update: I fix my leak down rate. Problem was there was a missing O ring on the pump assembly, the output O ring was missing. Pressure is holding now.