Help me diagnoss OBD1 Miss

[Stomis]

Did the intake manifold gasket upper and lower and cleaned the EGR in Pzuzu today. Much to my dismay the miss I was experiencing is still there

After driving it home Im beginning to think its the TPS but would like some input. Heres the parameters

I get a code 44 which is O2 sensor too lean

Driving around normally the truck feels fine. No lack of power pulls to my normal economy shift point of 2500 no problem at 10% throttle

Im getting a miss above 3700 rpms. I mean feels like I hit the speed limiter no fuel completely hit the wall miss.

It is not dependent of gear, up hill, down hill etc.

Now heres what I noticed tonight. I get no miss all the way to 4800rpms if I keep my foot below about 50% throttle. I can slowly ease my foot into it above that 3700 rpms and BAM the truck stops dead.

Gotta be a TPS no? Only thing that has me thrown is the fact that OBD1 should throw a code for TPS out of range.

 

[Fordum]

Fuel filter........
You are getting a lean condition. If the sensor is correct, then you are not getting enough gas.
Fuel flow is sufficient up to a certain point, then the pressure starts dropping as the volume decreases.
Beyond a certain point the fuel need exceeds the availability, and you stall.

Easing up to high RPMs puts low loads on the engine, and drops the fuel requirement. The amount of fuel needed is due to load, not necessarily RPM. When you bog it, it tries to dump in more fuel and has none to give.

Eventually above a certain RPM, engine friction loads will require more fuel that it can get even with light external loads.

 

[Stomis]

Fuel filter........
You are getting a lean condition. If the sensor is correct, then you are not getting enough gas.
Fuel flow is sufficient up to a certain point, then the pressure starts dropping as the volume decreases.
Beyond a certain point the fuel need exceeds the availability, and you stall.

Easing up to high RPMs puts low loads on the engine, and drops the fuel requirement. The amount of fuel needed is due to load, not necessarily RPM. When you bog it, it tries to dump in more fuel and has none to give.

Eventually above a certain RPM, engine friction loads will require more fuel that it can get even with light external loads.

Hmmm just did the fuel filter. Wonder if the pump is on its way out.

 

[Stomis]

Fuel filter........
You are getting a lean condition. If the sensor is correct, then you are not getting enough gas.
Fuel flow is sufficient up to a certain point, then the pressure starts dropping as the volume decreases.
Beyond a certain point the fuel need exceeds the availability, and you stall.

Easing up to high RPMs puts low loads on the engine, and drops the fuel requirement. The amount of fuel needed is due to load, not necessarily RPM. When you bog it, it tries to dump in more fuel and has none to give.

Eventually above a certain RPM, engine friction loads will require more fuel that it can get even with light external loads.

Ok threw a gauge on it today. Heres what I got.

Fuel PSI spec from the book 41-46psi

PSI @ idle 28psi
PSI @ idle with regulator disconnected 43psi

So what does that mean? To me that sounds like fuel is fine but again thats not under load. I pulled the filter off and blew threw it no problem.
When I did the intake manifold gaskets yesterday I couldnt help but notice the FPR looked original, not that that means very much.

This is just speculation but judging by the condition of the outside of the tank if the inside is anything like it then the fuel filter sock is probably clogged. I guess theres only one definite answer and thats to change the filter and sock when I seal the tank.

 

[Fordum]

Well, just got power back on for the second time. Hopefully I will be able to reply this time.
If this keeps up, I'm gonna put my genset back online...........

If I'm not misreading what you posted, it looks like you found the problem.
The way I read it, normal pressure is supposed to be 41-46psi.
Your pressure is 28.
Thus your problem.

When you disconnect the reg. it jumps to 43. That seems to indicate that the pump is putting out enough pressure, but the regulator is not holding it. Sounds like a weak or broken spring in the regulator if its a bypass one like a K5.

Of course, you could still have another problem. Just because the pump can supply enough pressure at idle, does not mean it can hold it when the volume increases.
That is where the dirty sock would show up.
With low flow, there would be enough gas trickling through the sock to maintain the pressure, but when you called for more gas, it would starve the pump.

I would check the regulator first, and get the pressure up to snuff at idle and then see what happens.

Unless I misread the last post, of course.......In that case, never mind...

 

[Stomis]

Well, just got power back on for the second time. Hopefully I will be able to reply this time.
If this keeps up, I'm gonna put my genset back online...........

If I'm not misreading what you posted, it looks like you found the problem.
The way I read it, normal pressure is supposed to be 41-46psi.
Your pressure is 28.
Thus your problem.

When you disconnect the reg. it jumps to 43. That seems to indicate that the pump is putting out enough pressure, but the regulator is not holding it. Sounds like a weak or broken spring in the regulator if its a bypass one like a K5.



Of course, you could still have another problem. Just because the pump can supply enough pressure at idle, does not mean it can hold it when the volume increases.
That is where the dirty sock would show up.
With low flow, there would be enough gas trickling through the sock to maintain the pressure, but when you called for more gas, it would starve the pump.

I would check the regulator first, and get the pressure up to snuff at idle and then see what happens.

Unless I misread the last post, of course.......In that case, never mind...

Im gonna order a regulator today and change that. Its only $20. Then tank has to come down to be cleaned, etched, sealed and por15d anyway so Ill check it then and replace it more than likely.

 

[TexasSilhouette]

What kind of fuel injection is this? It sounds like port injection. When disconnecting a vacuum reference from a fuel pressure regulator you should see roughly a 15 PSI increase in fuel pressure. It sounds to me like it is working perfectly.

 

[Fordum]

What kind of fuel injection is this? It sounds like port injection. When disconnecting a vacuum reference from a fuel pressure regulator you should see roughly a 15 PSI increase in fuel pressure. It sounds to me like it is working perfectly.

I'm not sure what he has. But, if I read his post right, the book calls for 41-46 PSI, and he has 28.
The pressure went up when he disconnected something, probably the vacuum line, but the pressure was too low to start with.

 

[TexasSilhouette]

If its manifold referenced fuel pressure it depends on how its supposed to be tested. I suspect it is supposed to be tested with the reference line disconnected.

 

[Fordum]

True.
Without knowing more about the vehicle, we are really getting nowhere, but we are getting there fast..........

 

[Stomis]

Its the 94 trooper. MPFI 3.2 v6 SOHC.

Im also getting an odd bucking on decel when not on the brakes.