Hello everyone I’m new here so I hope I get a chance to learn something from all of u. I have a 1986 irocz 305 tpi fuel pressure issue. My car has been running badly so I did a pressure test and with key turn on it goes to 35 psi and then immediately drops to 0 then I turn it off and on again it will go to 39 and drop immediately to 0 psi again. I checked the fpr and recently rebuilt it with new diaphragm and it didn’t smell or leak gas out of the nipple so I think the fpr is fine. Then I pinched the fuel return line and the fuel pressure went to like 45 psi and held for a good 7 min but I kno I didn’t clamp the line completely. I just took a flat pair of rubber line grips and squeezed the rubber line as hard as I could . So I kno after I pinch the line the pressure goes up and it holds . So what does this mean? Injectors leaky? Fpr? Can a fpr leak internally without blowing gas out of the nipple? Or is my fuel pump bad ? Any ideas? I’d appreciate any info. Thanks

 

Well with the return line closed, you help pressure. I think that eliminates anything to do with the pump and injectors. It must be the FPR allowing fuel to hit the return path at low pressure.

My results last time I checked fuel pressure on my 88:

Checked Fuel Pressure:
KOEO: 42PSI
Idle (W/Vacuum): 38PSI
Idle (W/O Vacuum): 46PSI

Leak Down
0 min: 42PSI
5min: 34PSI
10min: 25PSI
15min: 22PSI
20min: 19PSI
25min: 18PSI
30min: 16PSI

 

Thanks a lot man. I just ordered a new fpr and I’m gonna pick it up on my way home today. I think it’s the fpr too. Thanks for ur help. It really helps

 

Has this been resolved?

 

Hey bud I put the new fpr in and it held pressure at 45 but it still leaks down. So I’m going to check for a leaky injector tonight. When I pinch the return line it holds perfect but as soon as I let off now it leaks down but way slower than before. Any ideas? Thanks man

 

This tells us that your pump is working but something is the system is bleeding off pressure. Did seem a little low as well.


This should have eliminated the rail or injectors being an issue. Basically, as long as it wouldn't drain back to the tank, you held pressure in the system which is why I thought you had a poor performing FPR.


So if not the root of the issue, At least you are seeing higher than 43. Ideally with the engine running and with no vacuum on the FPR the golden number is 43.5, but it can vary. So, seeing 45 as opposed to 35/39 is an improvement.

If the return line is pinched and you are not losing pressure. This means your rail/injectors/connections/pump and all are not draining fuel out to the cylinders or tank. I am not sure what else you are goign to do to check the injectors, but I don't think it is necessary. Though, it never hurts to check anything.


Well, have you driven it? How does it run?

My pressure bleeds off on mine too and that is normal. My suggestion is to do a leak down over time and check the pressure every 5 minutes. The system will not hold 45PSI indefinitely. Do a chart like the one above( I am going to post it again) and then post your results. Some leak down is expected. It should be at a quicker rate in the first 10 minutes and then level off. The 16PSI at the bottom of the chart held pretty steady.

Leak Down
0 min: 42PSI
5min: 34PSI
10min: 25PSI
15min: 22PSI
20min: 19PSI
25min: 18PSI
30min: 16PSI

I had a leaking O-Ring that went to the 9th injector last summer. The car didn't want to start and when it did, it ran like crap. Eventually I found the fuel leak before I burnt the car down. As a disclaimer, I am not running factory injectors and I am still working on dialing my car in. So, I wouldn't say my numbers are gospel here, but I do know this is very similar to other results I have seen.

 

Thanks. I’ll check the Pringle’s on the 9th injector too.

 

And thanks Kyle I’ll keep u posted. Thanks for the advice

 

Ok I checked my prints in the fuel rail and the ninth injector one in the rail was bad. Now it’s holding pressure better but I’m still losing it fast in my opinion 0 min=45 psi 2 min=24 psi 3 min= 20 psi4 min= 15 psi 5 min= 13 psi 6 min=12 psi and then 12 min it was at 6 psi . It seems to hold longer below 20 psi . So I don’t kno? Any ideas. When I pinch the return line it still goes down but very slowly for example I’ll pinch it and it will stay at 43 psi for a couple min then drop by one psi in very slow intervals but still drops none the less? Any ideas? Thanks man

 

Also I’m pressure testing with out the plenum being on . I have the rails bolted down but the 9 th injector is just sitting unplugged but the line is hooked into the rail. And of course the feed and return line is hooked up. I don’t see any leaks anywhere;(

 

Pro answered this in the other thread you posted in. It sound like the drain back valve is failing in your pump. It's not a real issue if the pump is producing the fuel pressures you need while running. At the worst, it will cause a delay in starting if you key on, wait a bit, then try to start the engine.

Your 'running bad' can be a a multitude of things. Define 'running bad'. Is it misfiring/shaking hard while driving, not as fast as you think it should be, not wanting to idle ? 'Running bad' is rather generic term.
Did this just start out of nowhere? Is there a check engine light ? How many miles? When was the last tune up ? Are there mods that have been done ? How hard were the miles it has on it driven?.... the question list can go on forever... be more specific with the 'bad running' problem and it may be easier to help you diagnose/resolve it.

 

The plenum has nothing to do with it if you have the rail fully assembled.

I would be interested in how it runs now that you have a fully healthy FPR.