Fuel System Checks

[smagnotta]

Car has no codes. 87 Supra Turbo. Car has trouble idling after about 2 minutes after starting. Fuel pressure and vacuum fluctuate a lot.

I checked the fuel pump relay using my ohmmeter by measuring the continuity between terminals +B and FP. I get a reading and then it stabilizes at 0.1 (pretty low).

Then I check the continuity between terminals +B and PR and I get 81.5 (much higher).

I do get no continuity between +B and PR as expected.

Can anyone verify that the relay needs replaced?

I also checked the fuel pump resistor's resistance and I get a reading of 0.9 and then it stabilizes at 0.8. The manual says it should be approx 0.7. Isn't this close enough?

I checked the fuel pump operation by shorting Fp and +B on the check connector with a paperclip. I could hear the fuel pressure and my gauge on the FPR showed pressure. The fuel pressure with the vacuum sensing hose from the regulator disconnected was at 40 PSI and at idle was 30 PSI as expected.

However, in the manual it states that after stopping the engine that the fuel pressure should remain above 21 PSI for 5 minutes. This does not happen -- it slowly decreases pressure and goes below 21 PSI in about a minute and a half on its way to 0 PSI.

Any advice on what I need to replace or another check I could make?

 

[jetjock]

You're going to need a new meter pretty soon if you keep that up. As for the other thing you're losing rest pressure. It means you have a leak somewhere, either internal or external.

Does the fuel pressure fluctuate with the vacuum line off?

 

[smagnotta]

Thanks JJ...

No the fuel pressure does not fluctuate with the vacuum line off. It stays constant at 40 PSI. I am assuming that is a good thing.

With the vacuum line on it is at 30 PSI and then starts to fluctuate.

What would you suggest I try next?

 

[clifftrail]

check for vacuum leak

 

[jetjock]

I asked about pressure with the line off because your other thread says it's fluctuating. That shouldn't happen with the line off. If it did that'd point to a problem with fuel delivery. Since it doesn't fluctuate me thinks you're barking up the wrong tree regarding your idle symptom. It could be caused by lots of things (in this case a vac leak or a bad FPR) but for now fix the rest pressure since you found a problem with it.

Rest pressure (Toyota calls it residual pressure but I prefer the Bosch term) is when the fuel system remains pressurized to prevent vapor from forming (with the resulting hot start problems) during the first 30 minutes or so after hot engine shutdown. Keeping the fuel pressure raised increases the fuel's boiling point. It's no different from how your cooling system works. Preventing vapor lock is particularly important in setups like ours where the fuel pump doesn't run until the engine is cranked.

When the engine stops the injectors, fuel regulator, and check valve in the fuel pump seal off the system. That leaves pressure "trapped" in the supply side volume. Assuming you don't have an external leak one of those items is not sealing and letting the pressure bleed off. For example I've seen FPRs on these cars that bleed to the return line with the engine off. That shouldn't happen of course.

The diaphram on them tends to leak with age too. That can aspirate fuel into the intake manifold and cause all sorts of mixture issues. Few people ever check for this because you need a hand pump with a gage on it (for example a Mityvac) or some other way to see if the FPR is leak tight such as teeing in a vac gage and pinching the hose. I doubt that's your issue though, just pointing it out on general principle.

The fuel side of the FPR could still be leaking though. If a main injector (or the CSI) is leaking it'll also leak with the engine is running and send unwanted fuel in. See the problem with that? That's why you need to find out why your rest pressure is bleeding down. Myself, I'd start with the CSI and go from there.

 

[GuNDeZZZ]

wow very informative +1 to jj !!!!

 

[smagnotta]

Thanks JJ. I appreciate it.

 

[smagnotta]

OK checked out a couple things. The CSI time switch needed replaced (did so with a good one), and one of the VSVs (did so again with a good one).

The same symptoms occur.

I hear a loud whining in the engine bay when the car sputters and the fuel pressure fluctuates so I figure it's the fuel pump. I pull the hatch lever, walk back there and whatta ya know the thing is whining very loudly. When the car ran fine, I never heard it. Eventually the car stalls and the fuel pump gives a final death whine.