It's an all stock, all original '86 305 TPI motor. It's had problem after problem, now it's down to the last one, and nobody can figure it out. Here's the problem, it has a hesitation/stumble and at times it is pretty bad.

Ignition system has all been checked out, and parts replaced if needed. All sensors have been checked out, including the MAF, computer and prom.

I just put in a brand new AC delco fuel pump from the dealer, and a new fuel pressure regulator. The injectors are original with 73K on them. Fuel pressure specs out good.

Now, if I pinch off the return hose, the car runs PERFECT and makes great power for a stock 305. Only problem is, it's at 90psi at idle, and 80psi when you romp on it. Obviously I can't drive it like that.

What might cause that?

I'm thinking I might install an adjustable regulator, run it at 45-50 psi and see how it does. If that doesn't quite do it, I could install injectors for a 350.

I know it wouldn't be right, but I think it might work?

I would go ahead and install the adjustable regulator. Then hookup a fuel gauge that way you know the exact fuel pressure you are running.

The injectors could be bad. I put in Accel injectors on my 350 and they only lasted a few years before failing. If you want to test them to see if they are failling electrically, you can ohm them using an ohm meter. Obviously this will not show if they are mechanically failing.

Hope this helps.

I wonder if it's possible that your injectors are partially clogged or not opening all the way and no longer flow the 19 lb./hr that they originally did. So as you increase your fuel pressure by pinching the return line youre forcing the injectors to flow more fuel. I recently replaced the original injectors on my 88 and I was pretty shocked at how bad they looked. I don't know for sure if thats your problem but it might be worth a shot before throwing in the towel. Good luck.

They ohm just fine, I've even checked them at different times and temps. It worries me that you had problems with your Accels, I have a set in my other car that are 6-7 years old now.

I had that thought too. I talked to a couple mechanics that are really good troubleshooters, neither thought it was likely. Then again, one of them is the reason I changed the fuel pump, which didn't fix anything. I think I'll just go ahead and try the adjustable regulator, then the injectors. I have a set of ford yellow-tops sitting around I could use. They've been in the house, but it's been a while, maybe I should have them cleaned first.

Your FPR and/or injectors definately seem suspect. With pressure that high at the schrader valve it should be running extremely rich, but it's not. So it must be running lean normally. For what it's worth all of my original injectors ohmed out PERFECTLY before I replaced them. I threw in a set of Bosch IIIs and it's like a new car.

Does the car do this regardless of engine temp? I've heard that a bad reading from your coolant temp sensor will seriously screw up your A/F ratio. Just a thought. Let us know what you find out.

Yeah, it doesn't matter what the temp is. I had replaced the CTS too, as it was causing another problem. I don't know what could possibly be left that would make it run lean, other than injectors.

I made an adjustable regulator cover today, hopefully I'll get it installed tomorrow. It does run a little on the rich side with the line pinched off, but it's not bad... it runs smooth anyway. I'd like to play with the regulator and see what kind of pressure it takes to make it run better. Maybe it won't take a lot and then I can run a few tanks with injector cleaner in it.

have you taken a very close look at the reluctor pickup in the distributor? The connector and pins are well known to oxidize and pretty much melt away(plastic body), causing intermittent issues. My 87 iroc pretty much completely stopped working one day, and I went through a ton of crap before figuring that out.

if it does improve by messing with the fuel system, it's probably worthwhile to invest in a set of injectors though, if they are original. at the very least, have them cleaned and flowed, there are a few places that will do that job for around $100.00.

Distributor if fine, it's certainly a fuel issue. Well, it's not completely fine, there is a small amount of play indicating a worn cam gear (minor).

I installed my adjustable regulator today, I'm very happy with the results. It didn't need much of a boost in pressure and there is only a very very minor hesitation. Pressure is 45 at idle, then goes up to about 52 or so when you hit the gas. Certainly not high enough to shorten the life of the fuel pump.

The injectors seem to be HIGHLY sensitive to pressure, so they must be clogged to some degree. I'll drive it for a couple weeks, run a bottle or two of injector cleaner through it, then see what I have. If no improvement, I'll change the injectors.

Just to add an update, the car has been running fine, and getting 22+ mpg. I think I'll leave well enough alone and just have fun driving it