Hello all!

I have a 1986 Coupe (L98 iron heads) and I suspect that my FPR is bad. Here is what it has been doing for the past two weeks or so:

At erratic times, the idle stumbles (hot usually). I give it gas and it straightens out. There is exceptionally hard starting (hot or cold), but it eventually catches and runs (I originally thought it was fouled plugs, so I replaced them and everything was good for a day, then the same problems happened again).

Well, today the car wouldn’t start at work. I almost ran the battery down trying to get it started. I called my brother and had him bring me a timing light so that I can check to see if the plug wires are getting spark. They are. At this point the car barely starts and gets me home. I go to the parts store to get a fuel pressure gauge because fuel delivery is now my #1 suspect.

I hook up the gauge, and turn the key to run the pump. The pump runs, pressure goes up to low 30’s then IMMEDIATELY goes to ZERO when the pump cuts off. I start the car (typical hard to start) and the pressure is around 35 PSI, I rev the engine and the pressure may touch 40 and then return to low-mid 30’s when it returns to idle. I turn the car off and the pressure IMMEDIATELY returns to ZERO. There seems to be a faint gas smell in the vacuum line to the FPR, so I think it needs replacing.

I’ve read about the check valve being bad in the FPR. Would replacing the diaphragm and adding an adjustable unit fix my bad check valve problem? Or would I need to purchase the whole assembly (with the aluminum base and all)?

What is the best adjustable FPR kit to buy? BBK, TPIS, etc??

Thanks!

 

Sound like you are on the right tract, I would replace with a stock unit no real need for adjustable if you have a stock motor. Not sure about the check valve, the adjustable ones I believe just come with a new spring and cover, if the original diaphragam is damaged you must purchased the repair kit also. That is why I would go stock less trouble do it once and it's done.

 

Well the engine isn't quite stock. It was rebuilt 4,000 miles ago with a mild COMP CAMS kit, forged pistons, larger SS valves, and a custom PCM for Less chip. The intake is stock though. I replaced the FPR diaphragm when the engine was rebuilt (4,000 miles ago, but this was also 9 years ago too). I was thinking about an adjustable unit since I really don't want to go back into the intake to do this again. Thought the adjustable FPR might net me a few extra HP.

 

If you have a nearly new filter, I would change it. Even if it is old. Filter, Sock and pump, reg, and then injectors.

 

Hi,

I also have a thread about a possible bad FPR.

On mine (1992 LT1) it was running rich-most plugs were fouled, cat was red hot! I purchased fuel injectors thinking one or more were sticking. When I started to take it apart, I noticed that the vacuum line (to the FPR) was filled with gas!

I ordered a new one-but it has not arrived yet. I will post my results.

Keep us updated.

Steven

 

I just purchased a replacement diaphram / spring for my stock fuel pressure regulator. Got it at Autozone for around $35 bucks. The old one looked fine, though. I think I read somewhere recently that the stock fuel pressure regulator is good up to 400hp? I forgot to get a fuel filter. When I removed the old one earlier and blew air through it, black dirt came out! I'm now thinking about draining the fuel tank through the return line just to be safe. I'm not sure how much fuel will come out that way, though. I disconnected the coupling near the filter to blow out the section coming from the fuel rail in case any dirt or old o-ring fell in it during disassembly and fuel ran out like crazy so it seems like a good place to siphon. Also blew out the line from the filter to the fuel rail.

Good luck with your fuel problems, JXace. I'm interested to see how you resolve it.

 

Are you still running stock injectors pound wise, you might see some gain. It might cost a few more dollars going with an adjustable and a new diaphragam kit but you will have more control over your pressure. I wouldn't go to high on the pressure because of your tune. You should drive it more with the gas nowadays letting them sit messes things up. Good Luck

 

The car sat for most of the 9 years in my garage (after the engine rebuild) while I restored the rest of the car. I just put it into daily driving service about 4 months ago (straightening out a few issues here and there). The injectors where purchased from Mid America Motorworks back in 2001 (stock flow rate; replaced with the engine rebuild)

The FPR diaphragm was replaced also back in 2001 when I replaced the injectors. Perhaps sitting for so long caused the part to fail.


Pkazsr-

The fuel tank was completely drained and cleaned late last year. I replaced the fuel pump, strainer, and filter with NAPA units. I may just change the fuel filter just for fun since it is inexpensive and easy to do.

 

I have been having problems on my 93 as pressure was low. Replaced FPR with stock replacement still low. Bought a Aeromotive unit Part # 13106 for LT1 adjustable and got pressures up, but my pressures are not holding after shut down, whereas before they would. I am sure they had a regulator for your application. Mine bolted right in. I did add an extra O-ring to return line as it was loose and threads bottomed out before it got tight against O-ring, and had to bend the tube slightly to fit on the hold down bracket.

 

rubber parts used in the fuel system will begin to dry rot if they are not kept wet with fuel, this includes the injectors. Even if it looks fine, it could still be losing pressure. There is a way to test it.

Hook a fuel pressure gauge up to the rail and start the engine. You should get about 38-43 psi at idle. Shut off the engine and watch the pressure, it should drop very slowly (maybe 10 psi in 30 minutes). If not then you likely have a leak somewhere. Clamp the return fuel line (the rubber part in front of the engine), turn the key to on so that you pressurize the fuel system and watch the pressure gauge again, if the pressure is falling at a normal rate then you have found the problem. Replace the regulator.

 

Okay...

I just finished installing a new fuel diaphragm and it did not solve the issue. I've double check and I've made sure that I do not have any external leaks anywhere.

After the new FPR was installed, I had my brother sit in the driver’s seat and crank the car. I was at the back where the fuel pump is located to perform the return line pinch test (cannot do it at the front passenger side rubber lines).

Car is running….I tell my brother to turn off the car and as he does it, I pinch the return line at the top of the tank. The fuel pressure gauge increases from 38 to maybe 70 (car still running, about to be shut off) and as soon as the engine is off, the pressure immediately returns to ZERO.

So now the only thing(s) left have to be fuel injectors. Could injectors that are stuck cause the fuel pressure to IMMEDIATELY go to zero??

Things I am certain of:

Fuel pump is working okay.
Fuel lines (feed and return) are clear and functioning (due to increase in pressure when I pinched the lines).

Any tests I can perform on these Mid America Motorworks injectors…..any recommendations on replacements?

Any thoughts?

 

Talk to Jon @ FIC for the Bosch lll's great injector, great price, and great customer service there is a sticky top of tech page. You might want to check your cold start injector also. You can test the resistance of the injectors to see if the coils are good 16 ohms do that cold & hot but that will not tell you if one is stuck open but if they are bad it will lead to hard starting

 

I was just looking at Jon's website. I will call him first thing in the morning. Luckily his shop is in Cummings, GA and I live in Marietta, GA....I should have the parts pretty quick...his prices are really good! I paid out the @$$ for the injectors that are in there now back in 2001....

I did ohm test the injectors, all ~16.4 cold and ~17.3 hot

 

JXace, 1988_chris is having the same problem I think. When hot it runs lousy. All of his injectors also ohm correctly. You might want to send him a pm to see what he's done and add what you've done. Maybe the injectors are not the problem? I don't know enought about fuel injection to speculate, but two are better than one when it comes to problem solving. Hope this helps you both.

 

I just posted on 1988_Chris's thread.

The first occurrence for my problem was right as the car was warming up.....maybe about 160 degrees....the car's idle would drop and struggle, I give it gas and it comes back to life....if I'm moving, everything is cool. There were one or two instances where, while moving down the road, the car would feel like it, for a brief second, loses power.

I thought it was the spark plugs at first, so this past weekend, I replaced them and ohm checks the plug wires (which are fairly new).

 

The other thing you could try is to run the car and before shutting it off disconnect one injector see if you can find the faulty one by amount of pressure drop. 38 lb running sounds OK, I'm not sure about pressure with line pinched. Have you tried listening to each injector while the car was running by using a long screw driver you should be able to hear them clicking. Just hate to see you spend money and time installing injectors if they are not the trouble. Good Luck keep us posted

 

It looks like you covered most of the bases, however in reading all the posts I did not see any mention of the check valve in the fuel pump.

The pump may by producing pressure and the FPR working, but if the check valve is bad, the system will not hold pressure when the pump is turned off. It might be worth a look if you have not yet.

 

Fuel pump check valve? Is that the same as the "pulsator" that goes between the top of the pump and the main fuel hard line in the filler neck assembly? I never had it on this car since I got it. Currently there is a piece of fuel injection hose in it's place.

Or is the check valve internal to thr fuel pump?

 

I went through a very similar problem with mine, but mine wouldn't start at all when I bought it. My problem was a leak in the line leaving the fuel pump.

I have not seen this mentioned:
Someone had me pull off the fuel rails with injectors and all still attached to the rails. Hook up your fuel guage to verify the pressure drops. Have someone prime the fuel by turning the key on, wait for the pump to kick off, then turn the key off. If you do that enough, you will see if an injector is leaking out fuel. This method allows you to see all at once without having to actually start the car.

 

When I had my lines loose on mine a couple of days ago to see if there was blokage on the return line I checked the pressure line by blowing air back on that side but it did not leak back, so am assuming that the valve on the pump is ok. Also I eliminated the pulsator from pump to the rest of the line with hose as in the FSM gave me the indication that the pulsator was leaking as to why I was getting low pressure originally. So where is it getting air from as there seems to be no visible signs of fuel leaking? With the pressures that build up from a warm engine, I would think it would putting a lot in the cylinders?