To check for a restriction, you can disconnect the fuel return line at the firewall, connect a length of hose and pump the excess into a fuel container - or run a longer hose to the gas tank fill opening.

In the time it takes to do that test, you could replace the regulator, so I'd probably go ahead and replace the regulator.

Are you comfortable with the gauge accuracy?

Frank

I used a new Actron fuel pressure gauge. It's fairly inexpensive, but seemed to perform well. Since the pressure read in spec at the upper limit, it seems like the gauge is reasonably accurate.

With some contortions, it looks like the regulator can be replaced without removing the plenum. Can anyone confirm this?

Update. I got my ECU back from repair and drove with it for about a week. In park or neutral, cold or warm, the idle fluctuates from 1300 to 1700rpm at about one second intervals. When driving, it also fluctuates when coasting in gear once it gets to about 1700 rpm down from higher rpms. Switched back to the other ECU.

The other ECU does the same thing every now and then at idle, and always when coasting in gear once the rpms get to about 1500. Just less pronounced than the fixed ECU.

I don't think anything is wrong with the fixed ECU, it may be operating a little differently because of the new capacitors. Something is telling the ECU to vary the idle, since it happens with both of them. I just need to figure out what that is.

It isn't the fuel pressure regulator. After verifying that the low pressure fuel return line wasn't restricted, I installed a new OEM fuel pressure regulator. Pressure is now 40psi instead of 44psi with the old regulator, but the idle is still 1200 after warm up with the non-fixed ECU. And it still exhibits the fluctuation when coasting.

I found a JY distributor and capacitor/filter assembly last weekend, so I'll try swapping those out tomorrow.

im no stranger to the idle problems on these things, get your ISC and take it apart and remount the isc without the electronic side, turn the pintle all the way counter clockwise and start your truck. see if she's still idling funky. you may have a bad isc, and if you do... you can bandaid it until you can get one.

He's already metered the ISC and it was okay...

Dang DD, I'm going to have a beer in support of your efforts. This has been quite the saga for you. <img src="/forums/images/graemlins/frown.gif" alt="" />

That's a good idea 91Monty. Let's you take the ISC out of the equation just to make sure. I did it, and it still idles at 1200 with the pintle extended out all the way manually.

Replaced the distributor and noise filter and no change.

I'll have to think about this some more.