I've been having issues with my 89 for a couple weeks since I bought it. Intake backfiring, poor idle, severe hesitation, and more...

New injectors, plugs, wires, O2 sensor, and several other smaller things just for general maintenance...

I bought a fuel pressure gauge today and at idle it shows 32psi. rev the engine and the gauge bounces all over and settles back down as the engine settles in. Turn the key on and the guage jumps to about 5psi, something clicks and the pressure reads 0psi. Cycle the key and it does the same thing. Clicks and the pressure jumps to 5 and clicks again drops to 0... Running it sits about 32psi. what solenoid or switch controls the pressure to shut it off and on like this? If I'm not mistaken, the rail should maintain pressure at all times once it's pressurized, correct?

Should I just bite the bullet and replace the pump, regulator, and filter? (changing the filter no matter what)

Thanks!

 

When ign. switch is turned on the ECM will run the pump 2-3 seconds then pump is off until cranking /start position. The "click" you're hearing is likely the pump relay. Your key on pressure is low.

Ign. switch on position (Engine off) pressure spec. is 34-39 psi.
Engine idling should be 24-36 psi.--I usually see 30-34. I'd check the pressure regulator while running remove the vacuum hose at the regulator--pressure should increase roughly 4-6 psi. Also check for signs of fuel in the vacuum hose and regulator nipple the hose attaches to. Fuel on the vacuum side of regulator would mean it is bad. If the regulator checks O.K. ---you very well may have a partially plugged fuel filter--in tank pump filter or a weak fuel pump. Since you're repacing the fuel filter--that's a good idea for maintenance anyway regardless IMO. Another good way to check fuel pressure while running is to tape the gauge to the windshield to see what you have while driving. Anyway long story short your key on pressure at 5 psi is way too low.

 

When you turn the key on the ECM commands the fuel pump to run for approx three seconds to prime the fuel rail for start up ... the fuel pressure relay is on the drivers side firewall near the wiper motor ... it sounds like that part is working as intended ... the five psi rail pressure is kinda low ... check the fuel pressure regulator for fuel in the vacuum line visually then check the FPR with a vacuum tester to see if the diaphragm is OK ... If it checks OK then change the fuel filter ... with a GOOD brand ... if that doesn't help I would change the fuel pump ... they are not expensive and the C4 is probably the easiest car on earth to change pumps on ............

 

When you changed plugs - were any of them dark black and sooty?

The 5 PSI is awful low - can't believe it can even start at that pressure - it must come up to at least the 30s' once you're cranking for some reason.

There are 3 spots where the fuel pressure can leak down - you just need to figure out which one it is.
- Fuel pressure regulator: bad seal on the rail not shutting off fuel return or bad diaphram letting fuel leak past it into the intake.
- Injectors: The injector's pintle not stopping fuel flow completely and leaking down while there is no electrical impulse applied telling the injector to open.
- fuel pump check-valve - this would only impact pressure immediately after shutdown allowing the fuel to drain back into the gas tank.

That said - you have 32 PSI running - I'm assuming that's because you've got lower vacuum from the running issue. What does the pressure do when the engine is under load (i.e. how does it run while accelerating at say 2500-3000 RPM?) If the pressure drops then you've got a volume delivery problem (i.e. clogging fuel filter or bad fuel pump) - if it's running a little better and pressure is steady then I'd say you're looking at a bad regulator diaphram or leaking injectors.

Check the diaphram - that's the easy one. If that's good then you can try a heavy dose of some EFI cleaner if it drives well enough to run a couple tanks through (like 2-3x the concentrate) - otherwise sending the injectors off to be cleaned is probably the best bet as I've had so-so luck with the on-vehicle injector cleaner machines.

 

Bwiencek - The injectors are brand new Bosch III's from FIC on the board here.

I'm heavily leaning towards just replacing the whole thing, pump, filter, and regulator. Figure the equipment is all probably OEM and falling apart like me. Another Sunday project coming on...

I read when searching the board that if the temp sensor was bad it could be causing some of my issues. Is that accurate? If so, that may be some of the problem. I replaced the fan switch and thermostat and noticed afterwards that my temp gauge shows "LO" and once it warms up if reads 299 with the red light on. I'm replacing the sensor as well to see if that corrects the problem with the gauge.

Dang redneck mechanics!!! Hopefully I saved the car from him causing more damage!

 

Guess I skipped reading over the 'new injectors' part of the first post... my bad.

I'd check the fuel pressure regulator vacuum line as suggested (or cycle the pump on several times with it unplugged and see if you smell fuel there) and if it's not bad then the pump is suspect and a new filter probably isn't a bad idea anyhow...

if the computer is getting a low temp reading then it will stay in 'warm up' enrichment mode for a long time and think that the engine needs extra fuel to stay running until it gets up to temp (which it is but the computer doesn't know it!)

 

I just bit the bullet and am going to replace the pump, screen, filter, and the sensor. Figure it won't hurt... Between doing the brakes on my truck and the car, I will be freakin bent over cars alllll day...

 

Ok, so we are running again!!! Apparently the pump was bad. Hooked up the new one, cranked the engine and the pressure on the rail jumped to 42psi and stayed there! I've been out running around playing with the car all day for the first time since I bought it! It has a slight miss in it once it gets warmer, but thats for another day...

Thanks again for all the help!

 

I am glad the people here helped you. One thing to remember if you bought your injectors from FICinjectors Jon is the guy to talk to about your fuel system.