Really, until you confirm or rule out the fuel pressure everything else is going to be a shot in the dark. that can get expensive though.
If your old f/p tester is toast anyway, you could remove the valve completely in the schrader valve (don't lose it), cut the end off your f/p tester and clamp it on with a hose clamp. You've already done all the other obvious things so if you can get a reading on your pressure, if that's good we can start making some intelligent guesses but if the pressure's no good which your symptom's strongly suggest then all the other ideas become unnecessary.

 

Finally got the FP gage hooked up and i tested in accordance with the EEC Manual i have. So KOEO is 40 PSI. Idle is 32 PSI. With the regulator vacuum line disconnected 42 PSI. Now the manual calls to test the leakdown rate where you idle the engine than shut it down, than KOEO and note the pressure. Than you time it in a minute your leakdown should be within the same pressure as KOEO. At the beginning mine was sitting at 39. Well within range. However in a minute the pressure actually went up to 41. I sat there and watched the gage increase. I was expecting it to hold at 39 but not increase. I am assuming the regulator checks out fine. So i set up the gage so i can see it through the windshield and went for a drive. The pressure fluctuated as did the RPM. It was anywhere from 30-38 PSI. So once again i disconnected the regulator and plugged up the vacuum line and I still got the irratic RPM and pressure flucuation. So once again i believe the regulator is fine. I have noticed the FP increases when the RPM decreases. However later in the day i went to run some errands and finally got a check engine light.
633 4x4 switch closed
72 MAP out of range during Dynamic Response Test
542 Fuel pump secondary circuit fault.
It does not always pop on unless I am driving in the city with a lot of stop and go type driving causing the irratic RPM. I was thinking about replacing the fuel filter until i got the CE light. Now I am thinking the MAP sensor. However i dont know what to make of the 542 code.
Any thoughts?
Thanks for everyone looking.

 

So there is something funny going on with the fuel pressure but your leakdown test seems to indicate it's holding pressure.
Does the F/P drop, then the RPM drops and then the F/P starts increasing and the RPM comes back up ? That would kind of make you think the rising and falling pressure is causing the surging.
A couple of possibilities come to mind
Change the fuel filter just in case it's the cause of everything. It's cheap and it never hurts to have a new one of those.
The new regulator could be faulty - new doesn't mean as much as it used to.
The 542 code indicates an issue in either the relay or the wiring to the pump and back to the pcm - or the wiring in the pump itself.
Throw a relay at it for starters at least. Then start checking the wiring to the pump really carefully, especially the plug-ins.
Another thing to check just to be sure is your tps signal voltage.
code 72 - I didn't think 95's had 2 digit codes - sure you got that one right ?
That's all I got right now.

 

I still say change the MAP sensor.

 

You may be bang on with that, pressure fluctuations or not. For what it costs, it sure couldn't hurt.

 

From what i could tell the Fp and RPM seem to be inversely proportional to each other. I never saw the FP and the RPM fluctuate down together or up either. For a while I was thinking the regulator may be going bad and not maintaining a steady pressure. When I removed the vacuum and plugged it the fluctuation remained. So I dont think it is going bad.
From what I understand the MAP sensor senses atmosperic pressure inside the intake and sends a signal to the computer. With that being said could the atmospheric pressure of the day affect the MAP sensor also? I am wondering because at the start of this thread which was summertime it would do this the first few minutes of running and go away. Now it is constant also with colder temperatures and a lower atmosperic pressure.
I will have to do a search to find the fuel pump relay and figure that out. Can I test the old one for resistance or current flow before replacing it? Im not too great with electrical side of things but I can manage.
Also I was suprised to see a two digit code also but I ran the test twice because the reader was delayed at first. I got the 633 and thought oh great thats all? Than it started sending out the other codes finally. This morning driving to work it didnt throw the CE light at all.
As far as I know there should not be anything wrong with the wiring. Its a pretty stock truck other than the lift I put on. On second thought. Does the fuel pump wiring run through the drivers side door sill? The previous owner installed steps to get into the cab and ran the bolts straight through the wire harness causing all kind of issues with the transmission and OD light. I found it one day and replaced all the wiring that was burnt.
I think I will start with the fuel filter and MAP sensor. I want my truck back. This does happen whether I am on the front tank or the back tank. It is not picky.
Thanks for the help

 

Fuel filter and map sensor are a good idea. The map sensor can get coated with crap and misread. Sometimes you can just clean it with sensor cleaner.
The relay is in the black box under the hood beside the air filter. You can swap it out with one of the other ones in there to test, but they're cheap anyway.

 

I was wondering if the MAP sensor could be cleaned or not but I was reading that pretty much the only way that you could test it besides a vacuum pump would be some tester that reads the frequency or something. Sorry Im not an electrical engineer. Would you spray the cleaner into the vacuum port Im assuming? Hopefully this weekend work depending I can install a new filter and MAP sensor and go from there.
I will have to look for the fuel pump relay.

 

So I tested for codes again and I got nothing.
All I got was the usual.
633 4x4 switch closed
111 system pass


I have not made it to the store yet but I am uncertain now what to do next without just throwing parts at the problem and hope I get it right. I was hoping it was the MAP sensor.
For now I believe a good plan would be replace the MAP sensor and fuel filter and have the auto store test the ICM.
Than go from there.
Any suggestions?
Thanks a lot.

 

I went ahead and swapped the relay for the fuel pump with another one and no change. So I have been looking last night for an exhaust leak that seems to be getting lounder and noticed a trail of green coming out of the drivers side exhaust manifold around number 4 cylinder. It does lose fluid but out of the gasket around the thermostat. When I pulled the plugs they all looked good. I need to look at the oil to see if there is an issue with radiator fluid mixing into the cylinders. I noticed a bit of green and oil on the drain plug for the oil pan.

Could this be the cause of the running rough?

 

Not to be an a** but # 4 is on the passenger side, 5-6-7-8 are on the driver's side.
Could the coolant be coming from the intake and rolling around to the exhaust manifold ? Only other place I can think of is the head gasket.
But either of those things could cause running problems

 

Sorry. I thought it would one or the other so I went with it.
I am quite sure it is coming from the head to block area. You can see where it has come out from the mating surface and accumulated on top of the exhaust manifold flange for #8 cylinder. Than it runs from there down the block and the oil pan.
It would only make sense that this would be the cause of the poor running condition. Everything that yall have suggested and I have tested has checked out fine.
Problem is I do not have the space, time or money to continue sinking into a 21 year old truck with a thousand miles shy of 200k. So I may have to consider my options on how much farther to go. This sucks as ol blue has been real good to me.

 

So today in traffic I decided to shift the transmission into first gear to see what would happen. I have noticed that if I take overdrive off while rolling at 45 mph or so it doesnt surge. I was at a standstill and started moving again in first gear and no surge. I shifted to 2nd no surge. Drive with OD off, no surge. I repeated this a couple of times and no surge. I tried it in town and also drive just fine. So is there a sensor that tells the pcm what gear you are in and affects the engine rpm. Im wondering about the VSS or perhaps the sensor on the side that is connected to the shift lever I forget the name.The transmission is an E4OD. Can you test either of these with a multimeter? I still do not have a CE light which now definetely tells me that there is nothing wrong with the engine other than a coolant leak. I do not have the OD light flashing either.
Thanks.

 

Just remembering also a couple of years back I had the rear end rebuilt. I had to take it back due to the speedometer bouncing and doing odd stuff. They replaced the VSS sensor and the ring inside the diff and all was good. The speedo works just fine but I am wondering if the sensor could be having a problem.

 

The vss is a magnet basically, so if you have microscopic iron filings in the fluid it can get coated and not read the spaces in the tone ring. Or if the tone ring gets all gummed up, same thing.
You could try pulling the vss and wiping it off.
At least now you seem to have narrowed the surging down.