Fuel pressure problem

[SpiderGirl]

I have been trying to get my ‘82 Spider on the road for several weeks now. It sat in a field for 30 years so I had a lot to sort out with the fuel injection system. I’ve replaced many of the fuel system components- cold start valve, AAV, fuel pressure regulator, injectors, temp sensor and filter. I’ve also replaced anything I can think of that could be at fault with the ignition system- plugs, cap, rotor, wires, vacuum advance pod. The car starts and idles fine, and will run well with plenty of power for 2-3 minutes. Then it sputters and backfires at engine speeds over 3000 rpm. I checked fuel pressure and it’s at 25lbs when idling. It starts to sputter when warm and parked at 3500 rpm, and at WOT engine speed goes down to about 3000 with lots of popping and backfiring. Fuel pressure goes down to about 15lbs under those conditions.

I always thought electric fuel pumps usually work or they don’t. So I’m suspicious of something upstream of the pump- I didn’t remove the tank but did remove the sending unit which allowed me to clean it pretty well in the car. I’m wondering now if there isn’t a filter in the tank- but I don’t see how there could be because it appears the outlet and return are in an inaccessible part of the tank.

Timing is set at 10 degrees BTDC. I don’t think there are any vacuum leaks, I pulled the new filter yesterday and it was fine.

I’ve got another pump but wanted to see if anyone had any other ideas before I spent the time to install it. I’m so close! Hope I can get this solved and the car back on the road this week. Thanks for help!

[spider2081]

I believe 15 lbs of fuel pressure is about where the engine will stop running. The fuel pressure should remain above 25 lbs through out the full RPM rage. Actually it should remain above 25 lbs with the engine not running if you hold the air flow meter vane open. You did mention replacing the fuel filter. Was the original filter( did anyone) cut open to inspect what was in it? Also the fuel tank has internal baffles, unless you are using a borescope to see the other side of the baffles you have not seen the area where the fuel pick up tube is.
Where are you measuring the fuel pressure, most of the time its measured at the cold start valve hose. Can you put that hose in a plastic bottle and operate the fuel pump to see if the fuel is clean?
I would not replace the fuel pump with out knowing the fuel tank is clear of rust, as rust particles could ruin the new pump fairly quickly. Chances of a car sitting years in a field and not having lots of rust and water in a fuel tank are pretty slim.

[SpiderGirl]

The fuel filter that was on the car when I got it was never cut open, but it was also not clogged.

You're right that I can't see what's on the other side of the baffle. My suspicion is there is rust scale in that part of the tank and it's large enough pieces that they are not actually passing through the pickup tube but rather being sucked partially into it when the car has run for a few minutes and restricting the flow.

The fuel coming out at the cold start valve is clean.

I suppose my only option now is to pull the tank and clean it.

[18Fiatsandcounting]

Did you change the timing belt? If so, it's possible that the camshaft timing is off, which can cause the issues you describe.

If your spider sat for 30 years, then it definitely is time to change the timing belt.

Check also that the distributor advance is working. Easiest way to do this is to idle the engine and with a timing light, verify the engine is at 10 BTDC as you noted, then rev it up and watch to see that the timing marks move. If they don't, the mechanical (centrifugal) advance inside the distributor could be stuck, which wouldn't surprise me at all after three decades. And that will cause poor running and a lack of ability to rev the engine much past 3000 or so.

-Bryan

[grrrdot]

The fuel filter that was on the car when I got it was never cut open, but it was also not clogged.

You're right that I can't see what's on the other side of the baffle. My suspicion is there is rust scale in that part of the tank and it's large enough pieces that they are not actually passing through the pickup tube but rather being sucked partially into it when the car has run for a few minutes and restricting the flow.

Are you seeing 25 psi at idle when everything is warm?
What happens to the fuel pressure at idle when you pull the vacuum line at the fuel pressure regulator?
When its all warmed up is the fuel pump getting hot? The engine does not need much fuel volume free revving to 3500RPMs, if the pump was struggling to pull enough fuel to maintain pressure I would expect it to get quite hot.

-G

[Bagneaux]

I have always replaced the tank in all four of my Spiders and X1/9s too, even when they only sat for a year or two. . I agree that rust scale in the tank is probably the problem.

[wizard124]

My suggestion is to hook up a clean fuel source to your existing fuel pump.

If the sputtering reoccurs, then change the pump.
If it runs smooth, then the tank is the problem.