Help! Limp Home Mode

[lamarZ06]

...antz....

Sounds like that poor connection at the pump could be the cause of your problem.

....Just lettin' off a little steam ..Hell,I can't afford 'Webbers'...haven't changed the harness just yet...But like you said FPR....cars outside under a tarp w/anifreeze...it's turning cold here... won't be the first winter it has spent under snow. If that's it..the FPR may have to wait 'til spring. If not break out the snow chains n' go ice racing... let ya know.. lamar

 

[lamarZ06]

....antz....

Not sure.
if you turn the ignition on but don't start the fuel pump shouldrun for 2 seconds. After that does the pressure stay up or does it drop back down?
there's two checks that can be done on the FPR.
Disconnect the vacuum line to it and make sure no fuel comes out.
The other check (can reconnect vacuum line before this) is to clamp the return line (believe this must be done at the tank) and see if the pressure drop continues. Be aware when you do this the pressure could (and most likely will) go higher than 40PSI.

...I clamped the return line and started motor.. pressure went to 40 psi. ..I ran it at idle aprox. 1 min..then pressure dropped...before.. motor would show 40 run few seconds pressure drop to 20/15 to stall. Does this point to a cause? thanks..

 

[Antz81]

...I clamped the return line and started motor.. pressure went to 40 psi. ..I ran it at idle aprox. 1 min..then pressure dropped...before.. motor would show 40 run few seconds pressure drop to 20/15 to stall. Does this point to a cause? thanks..

It eliminates the pressure regulator. (For now) have you got the connections at the pump sorted yet?

 

[lamarZ06]

..Hey ANTZ...

It eliminates the pressure regulator. (For now) have you got the connections at the pump sorted yet?

...Re-wired ..I felt as you do about the FPR...I don't really know how the FPR works half open, full open..It regulates pressure ...just don't know how...I have seen the diaphragm..Thanks

 

[Antz81]

So, new pump with good connections, new filter, FPR seems to test fine. Next thing i would suspect is a leaky injector(s) or a leak near the pump.
This is why I asked about what the pressure does if you turn the ignition on (runs the fuel pump for 2 seconds) but don't start the engine. I suspect if you try this you'll find the pressure drops back down again. It should be able to hold pressure for about 10min.

On the fuel sending unit where the fuel pump mounts to, there was a pulsator that some people remove and replace with a short length of rubber fuel hose. If they didn't use the proper type of fuel hose it could be leaking or the clamps could be loose.

Start off by measuring the resistance of each injector coil. You should get around the same reading for each injector. (about 12.5ohm from memory)
This is only checking the coil, but may give an indication of any that need replacing.
I've never had to leak test an injector, so I'm not sure of the proper procedure for this. If you search some older threads you may find it, or someone else here might be kind enough to explain it here for you.

 

[lamarZ06]

Antz81

So, new pump with good connections, new filter, FPR seems to test fine. Next thing i would suspect is a leaky injector(s) or a leak near the pump.
This is why I asked about what the pressure does if you turn the ignition on (runs the fuel pump for 2 seconds) but don't start the engine. I suspect if you try this you'll find the pressure drops back down again. It should be able to hold pressure for about 10min.

On the fuel sending unit where the fuel pump mounts to, there was a pulsator that some people remove and replace with a short length of rubber fuel hose. If they didn't use the proper type of fuel hose it could be leaking or the clamps could be loose.

Start off by measuring the resistance of each injector coil. You should get around the same reading for each injector. (about 12.5ohm from memory)
This is only checking the coil, but may give an indication of any that need replacing.
I've never had to leak test an injector, so I'm not sure of the proper procedure for this. If you search some older threads you may find it, or someone else here might be kind enough to explain it here for you.

Antz...when pressure drops to 20/15 the wires at the tank were moving in concert with pulsator.What the hell is that for/ Is this what I had confused 'limp home' with. replace or re-route? And what action engages pulsator? You have been a tremendous help. Maybe getting closer to the truth......sure glad I didn't start throwing money at it ...The pump is about 4 months old. seaching images....................

 

[lamarZ06]

...Thanks for your help...ground to fuel pump harness was at fault...

...your help through this mess helped me zero in on malfunction...ended up cost me $12.95 / harness; after 30 years it was time for a new one............thank you......lamar

 

[Hib Halverson]

From the posts here, it's obvious, you've purchased a major "project".

The nominal key-on/engine-off fuel pressure should peak at 40-42-psi, then drop slightly once the pump shuts off but then should hold for several minutes. If you're down to 15-psi after 30 seconds, the car has a problem in the fuel system. It could be a number of causes: leaking injectors, bad FPR, restricted fuel lines/filter, faulty fuel pump and so forth. To properly diagnose the problem you need the Factory Service Manual, which you can buy from CAC sponsor Zip Products, and it's fuel pressure test section.

A couple of questions:

1) Is the check engine light on?
2) If it's not on, does the check engine light come on then go off during "bulb check" when you key up?
3) If not, you need to find out why it's not coming on during bulb check...again the Factory Service Manual is the place to look for info.

Those are some starting points for you.

 

[lamarZ06]

thanks HH............

I was able to trace problem to wire harness at the tank/12$S..Thank you for your interest and time...lamar