[QUOTE=Suzonda;3313970]He just said it... right there... can you see it?...[/QUOTE]


No, just to break it down for you, (Suzonda) as you seem to have trouble reading, comprehending, or telling the truth for that matter

mkc1962 states at idle it holds 45psi. (see post 1 and 42) when trying to rev the motor he states it is at 40psi. (see post 70). If the truck drops from a idle of 45, down to 40, that is a problem.

Oh, and if anyone would like to know why I question your ability to tell the truth? Take a look at this post #749.
https://dodgeforum.com/forum/1st-gen...p-pics-75.html

Still waiting to see underhood pictures of the 90 dakota with a 5.9 cummins, and dana 60 front and rear axles!!!! LOL

 

Quote:

Originally Posted by mkc1962

Suzonda, thanks.


Maybe my reply to 93ragtop was a bad choice of words at the moment. Revving up I meant when running, not just goosing the the throttle while sitting still. I have run it more than once down the road, with a fuel PSI guage installed at the testing "T" on teh injector fuel rail. (Ive tried using both of my guages craftsman/Snapon to eliminate bad guage theory). Whether at idle, goosing sitting still, or full throttle at 70 mph, it holds a pretty consistent 40-42 psi. Now mind you, when I say full throttle, I do not get a full throttle response back from teh engine, instead it just bogs down like it running out of fuel or some other issue.


This bogging/lack of acceleration happens even at the most basic slow opening of the butterfly, but if you gently ease it through sometimes it revs up just fine. If you just all of a sudden push it down hard all you get is a deep gulp of nothing often followed by a slight backfire....but all this going on it never dies it just goes back to a nice normal idle once butterfly is released.

mkc1962, Do you know what the factory pressure is supposed to be? I dont have books for the 96, but on line I found a couple of places that said 45 and one place said 45-55.
Here is my theory on what may be happening, and again, I could be way off. Most all of my experience has been with chevy on this, so, take this for what its worth.

Assuming it is 45 and you are at 40, that would be about a 10% loss in fuel.
Usually an engine is set to cruise at 14.7 to 1 fuel ratio. The engine would be in closed loop at this time, so if it was lean, the O2 sensors would detect this condition, and correct it back to the 14.7 to 1. ratio.
Once you put a load on it, ie reving it up, trying to accelerate hard, etc. the computer will switch out of closed loop and run in open loop.
Open loop are pre designed tables built into the computer. They will use engine rpm, throttle position, map, etc to determine the amount of fuel to inject.
Usually it is designed for about a 12.5 to 1 ratio.
Now, here is where I think could possibly be a problem. If you are loosing 10% fuel pressure, then when the motor needs a ratio of 12.5 to 1, you are only getting about a 13.75 to 1 mixture. (too lean)
This may not be your problem, but I wanted to throw it out there.

My other suggestion would be, if possible, find another computer and try it on the truck. It seems there are a lot of problems with repaired computers.

Good luck and I hope you get it figured out.

 

not 100% sure what the tech book says it is supposed to be at this point as its been so long since I last did that, but clearly recall it being in the mid 40's. All of my testing so far have shown it to be in that range. And to some degree agree with you rline of thinking. But, Ive seen many FI vehicles that Ive tested over the years that would say call for 45, only show maybe 40 and run just fine....usually when I'd find one that was pressure related it would be a situation where it would call for say 45 but only have 20...then it would be a starved situation, easy to diagnose.


As for the ECM....it is the original that had a very clear not firing to 2 injectors issue. I sent it out to have it tested and repaired. They confirmed that it did have an issue of loose solder connections on the two injector outputs and that after repaired did pass all bench tests. Fully lifetime warranted. upon return was easy to see that now all 6 were clearly firing. I have no obvious reason to suspect further issues with the ECM.


I do appreciate all the opinion and ideas.

 

Yes, I tend to agree, the pressure drop would not likely be enough to make it run that bad.
On my chevy motor, the factory pressure is 43 when idling but when the vacuum hose is pulled I think it goes up to 48. But I dont think the dodge has a vacuum line on the regulator. My 87 dakota is carbed.

Again, with the chevy computers, from what I have read on another forum, there seems to be a lot of problems with remanufactured units.

If I read correctly, you test drove it with no converter or exhaust hooked up. So that should eliminate an exhaust restriction.

Im out of ideas. If I can think of anything else ill post it. Hopefully you will figure it out soon.

 

Straight from the 96 FSM

"With engine at idle speed, system fuel pressure
should be approximately 241-310 kPa (35-45 psi)"

a bigger range than I remembered but obviously in the case of these dodges its a normal thing that mine clearly falls in the range of.

yes I drove it up the driveway with the cat removed and it did the very same thing. That was one of the first tests I did several months back.

 

What's the brand and rated pressure range of the new pump? Under load it should be hovering at around 49psi so either the line from the pump unit to the outlet at the top of the sending unit is kinked/damaged or you have some regulation issues. Honestly I'd try taking a air gun, stick it in the line at the pump end @15psi and see if you get anything out the other side. Take the line off the fuel rail of course. Sometimes crap can build up that slips past the siphon filter and cause some issues.

Also... Recheck all gaskets to do with intake. Even the slightest little shred of missing TB gasket can cause a ****load of issues.

 

The fuel pump was not replaced. The regulator/filter was replaced, and all lines were blown out as you suggest with nothing but pure gas coming out the other end into a clear jar. Fuel rail completely blown and checked as well as new injectors.

Though I appreciate the input I have no idea of where you are getting this 49 psi but what like to know.

TB gasket was replaced last week again when I removed it to install the new injectors.

According to the 96 FSM

FUEL SYSTEM PRESSURE TEST—3.9L/5.2L
ENGINE
The vacuum assisted fuel pressure regulator
located at the rear of the fuel rail is no longer
used on the 3.9L or 5.2L engine.
Fuel systems on the 3.9L/5.2L engines are
equipped with a fuel tank module mounted, combination
fuel filter/fuel pressure regulator (Fig. 8). The
fuel pressure regulator is a mechanical device that is
not controlled by the powertrain control module
(PCM) or engine vacuum.
Fig. 14 Fuel Pressure Test Port—Typical
With engine at idle speed, system fuel pressure
should be approximately 241-310 kPa (35-45 psi).
(1) Remove (unscrew) the protective plastic cap
from the pressure test port on the fuel rail (Fig. 14).
Connect the 0-414 kPa (0-60 psi) fuel pressure gauge
(from Gauge Set 5069) to test port pressure fitting on
fuel rail (Fig. 15).(2) Note pressure gauge reading. Fuel pressure
should be approximately 241-310 kPa (35-45 psi) at
idle.
(3) If pressure is at O psi, connect DRB scan tool
and refer to operating instructions in the appropriate
Powertrain Diagnostics Procedures service manual.
If operating pressure is above 45 psi, electric fuel
pump is OK, but fuel filter/fuel pressure regulator if
defective. Replace fuel filter/fuel pressure regulator
assembly.

This afternoon I had some time to try and do a video. However looking at it now sitting at my computer, I am not sure if the sound quality is good enough to get the point across....Once again took it for a road trip with the fuel pressure tester applied, at idle or sitting still attempted revving it stayed in about the 40psi range and going down the road got to 42 under load...these are well within the ranges that the Dodge FSM says it should be.

 

If it was a carb vehicle, you would think a bad accelerator pump.

Its just a guess, but if it was mine, I would like to find another computer and try it. But looking on rockauto, it appears 96 manual transmission is a one only computer.

 

my same thoughts IF it were a carb...and in many ways I still prefer carbs, lots easier to troubleshoot and I do still own many classic vehicles that have them.
I've been looking at local wrecking yards for dakotas but no luck so far. I already paid $120 to have my pcm repaired and tested, It did have issues, but the report back was that it tested good after the repair. If you cant get a reliable rebuild at a place that does only that, who's to say a remanned unit from Rock or any other parts house would be any different. Even if out of a salvage car, I'd be interested to see if ANOTHER one in any shape acts any different.

 

If it's a 96 ..

Pick up a bluetooth OBDII reader (the better ELM327 units), and install Torque (Free or Pro; Free is free, last time I checked Pro was like $5) on a Android device; then do some data logging of the sensors, and see what the ECU THINKS is happening.

RwP