1991 TA 305 TPI. When car warms to operating temp it develops a terrible off-idle stumble. Almost a stall condition! When cold it is better, not great, but generally drivable. Honestly, sometime the stumble is better, sometimes worse…it is not consistent! I think it is related to the low fuel pressure…but would appreciate help!

Fuel pressure with:

Key on- 26 psi
Cranked/idle- 33psi
Vacuum line disconnected and plugged from FPR- 33psi (I know it should increase, but it does not!)
NOTE: FPR holds a solid 12” vacuum when tested and the vacuum line to the FPR pulls 20” vacuum at idle
WOT- drops to 30psi, then rises back to 32psi
New fuel filter
Blew air through fuel lines (all disconnected!) to assure that there was no blockage.
I have replaced most components, tested injectors and all hover around 17.9 ohms hot and 16.8 cold.
NO CODES EVER!

Is the 33psi at idle indicative of bad fuel pump? Why does the FPR not increase psi when vacuum disconnected? I would assume, because the fuel pump is bad!
Anyone know what is wrong??? I do not want to drop the tank and change w/o being fairly certain the pump is the culprit.

Thanks for any help you can offer!!!

Note: I have searched the boards…may have missed some post …but can’t find any help related to my issue!

 

sounds like bad fuel pump or clogged filter

 

The fuel pressure should be 43-47psi with no vacuum line on the FPR. Try and temporarily pinch off the fuel return line near the front driverside of the engine and watch what the fuel pressure does, (it should spike to ~60-70 psi). If it does spike then the problem is with the injectors, or FPR; if it doesn't spike then the problem is with the pump, pulsator, or lines. Check all the metal fuel lines to make sure none have been crimped or damaged.

Hope this helps.

edit: Injectors can be ok in an ohm test and still be leaking fuel.

 

Thanks to both of you for your replies! I blocked/pinched the return line and there was no increase in fuel pressure! So is this a sure bet it is pump??? There is no kink in lines and I have blown air through the feed line from filter to intake, while disconnected...the only thing I am unaware of is the "pulsator"...I am not sure what this is! "Taint one on a 4th gen...or at least I hope not...since I have no clue what it is! Thanks again...Jimmy

 

I'm having same issues, except I can't seem to get over 30psi FP. I have new injectors, FP regulator, all new o-rings, filter etc.

Everything I have found is leading to the Fuel Pump as well. Hoping to start taking it apart this weekend, but will be next weekend before I put the pump in and put it all back together...

Subscribed to thread, will keep you posted of my status. Let me know the results if you get a new pump installed before I do!

 

The pulsator is what connects the fuel pump to the metal fuel line on the tpi fuel pump hanger assembly. It looks like a small, metal brake master cylinder, no clamps; it just slips over the fuel line and the fuel pump outlet. I replaced mine with fuel hose when I did the pump.

 

What did the "pulsator" do? I just removed my pump today and it the rubber hose like you describe. It's olny been in there for about 6 years and the hose was falling apart, I beleive that is where my fuel pressure leak was.

 

The pulsator is a kind of secondary bellows to keep the "fuel pump pulses" from reaching the fuel rail and injectors. It is not strictly necessary and a new pump kit will come with a section of fuel hose to replace the pulsator...

I'll try to post a pic tonight...

Hope this helps.

 

Here is a pic of mine that I pulled out yesterday. That rubber line is only about 6 years old. Are there any other options besides rubber so I don't have to go through this again in 6 years?

 

Someone on another post said that I was most likely losing pressure because it was leaking from that line back into the tank. It makes perfect sense after seeing what it looked like.