Adj fuel regulator issue, maybe?

[1leg]

I have the CFM-tech adjustable style regulator, just wondering if anyone has had any issues with sudden lose (13 down 7) of fuel pressure and then it comes back with one of these. Truck will run fine for a while (days-weeks) then suddenly go to around 7-8psi. Typically it’s after it sat for about 2-3 hours after driving it. Very hard to diagnose because by the time I can work on it the pressure is back to 13 then it will not have an issue for a few days or even weeks. I have replaced the stock fuel pump with a good replacement; don’t remember the brand but it wasn’t the cheap one. Also replaced the fuel filter and problem has continued. The pre-filter on the original pump was falling apart so I was really thinking that was the problem. The only other thing I can think of is the fuel pump relay is going bad but I would think that it would happen more consistently if it was that.

Any ideas? Dose the computer control the voltage to the fuel pump in anyway?


1989 suburban 350 tbi, th400 trans.
New fuel pump and filter.

http://marine-performance-parts.com/images/products/detail/cfmtechadjregulator.1.jpg

[EagleMark]

Any ideas? Dose the computer control the voltage to the fuel pump in anyway? Nope!

Loose wire, bad ground, loose hose sucking air?

[1leg]

Nope!

Loose wire, bad ground, loose hose sucking air?

Thanks EM, I have been hunting for loose wire and grounds for weeks, Hose sucking air thats a new one can you give me lead on where or how to look for it, any know issues i should be aware of.

[EagleMark]

Anywhere before the pump!

Could also be a kink in any flexable line after pump? Could be loss of charging system during this time?

[lionelhutz]

Does it fix itself when you cycle power. I doubt it's the relay. A voltage drop in the relay contacts would quickly burn-up the relay.

I'd think it's the pump doing it. Either from loss of voltage or it's just bad. The hose from the pump to the sender unit sometimes fails and leaks fuel but I doubt a leak in that little piece of line would cause an intermittent problem.

[1leg]

Does it fix itself when you cycle power

Not completely, but after it sits for a while.
Has new pump and filter, about 1 month ago, problem contiued symptoms the same. Going to hook up a volt gauge right at the plug near the pump for the next time it happens to see it it's a voltage drop issue.

[JeepsAndGuns]

Are any of the fuel hard lines running close to a exhaust pipe? Could exhaust heat be boiling the fuel inside the lines and therefore getting a lot of vapor in the lines that take a little bit of time to work out? Just a random thought...

[Roadknee]

Does it fix itself when you cycle power

Not completely, but after it sits for a while.
Has new pump and filter, about 1 month ago, problem contiued symptoms the same. Going to hook up a volt gauge right at the plug near the pump for the next time it happens to see it it's a voltage drop issue.

Don't be surprised if you see a voltage rise issue caused by the pump partially and momentarily disconnecting from power. These trucks are getting old and the wiring is old. If you want to rule out everything electrical install a new sending unit, hotwire kit, and install a supplementary ground for the pump directly to the frame.

[1leg]

I have installed a volt gauge that is taped in at the plug near the tank. at least the next time it happens i will have something to look at currently reading 13.5 amps. The fuel lines are stock and this exhaust has been installed for more than 3 year. I have only had this issue for about 3 months. Only thing I have done in the last 4 months is spark plugs, fuel pump, fuel filter, cap and rotor. I did add a second battery about 1 year ago.

Today I also installed a 140amp alternator that i had built buy a local rebuilder finally, been wanting to do this sence I add the 2nd battery.

Thanks everyone for the help.

[1leg]

Ok the issue reappeared today, going to work, when I left the house had 13.5 when I got to work 4 miles had 13.5psi and 13 volts, left for lunch had around 10psi, volt gauge was reading 12.5 - 13 volts, left home to go back to work had 10psi and 12.5-13 volts’ got back to work and was still 10psi. Left work to go home and it was back to 13.5psi when I got home it was still at 13.5psi and 12.5-13 volts.

I'm pretty sure it is not a voltage or wiring issue. Leaning toward a problem with the fuel regulator, or something in the fuel line is blocking fuel. Going to reinstall the original TBI unit and regulator, then blow out the fuel lines. If the problem is solved I will pull the current TBI and fuel regulator apart to see what I find.

Just to remind everyone, 10psi does not make the truck un-drivable around town, however I have seen the PSI drop below 9psi and it is nearly impossible to drive however I have made it home each time.

If anyone has any other ideas please let me know.

[stegey]

curious if you have fixed it yet ? if not , ruled out electrical from what i've read . i would lean toward the rubber hose connection on the sender between the sock and the pump , possibly a crack or loose clamp ? a regulator would not be intermittent like you describe one would not think plus you would smell it if the diaghram was leaking . just my 2 cents . keep us updated.

[1leg]

I installed my old regulator and injectors and have not had any issue since. I also blow out the fuel lines before installing. I have not had a chance to take the adjustable regulator apart yet.

I suspect that either I had something in the fuel line that was blown out or something is wrong with the adjustable regulator.