Stutter and stall

[ahmincha]

Hello everyone as the title says I have a 1992 4.0 automatic. It has no codes in it when you start it up it'll run then it starts to stutter as the fuel pressure drops and then stalls at that point it'll mediately start up every time.

It has the new idle air control and throttle positioning sensor that are less than a year old. And also rebuilt distributor any help would be appreciated

[HOrnbrod]

Did you hook up a pressure gauge to see exactly what the fuel pressure is doing? Sounds like the pump might be dying or it's starving for fuel.

[ahmincha]

Merry Christmas 

Yes i did have a gauge hooked up. 30lbs psi with vacuum hooked uo 40 with out. it will sit and idle for a few minutes then guage will show loss of pressure and it starts to stumble then stall at 0.

then when you immediately try to start it it starts right up. fuel pump was replaced 1 yr ago 

I did make a short video but its still to large to post  

[HOrnbrod]

Try bypassing with a jumper wire the fuel pump ballast resistor on the left inner fender, engine bay. My 91 has one so I assume your 92 has one too.

 

Have you checked codes using the ignition key? If not, do that.

 

https://comancheclub.com/forums/topic/28111-reading-obdi-91-and-92-mj-fault-codes/

[ahmincha]

I did the bypass and also checked codes no codes and the bypass same results 

[HOrnbrod]

Did you get the 5-5 code when you checked codes?

 

Last fuel filter change?

 

I'd try a fuel pump flow rate test from the fuel rail port or at the output of the fuel filter. Using an adapter hose the pump should deliver a minimum of one liter of fuel into a bucket in a minute.

[ahmincha]

I did get the 55 code. 

the weird thing is truck runs fine gauge attached as I am watching the gauge starts to wiggle then starts declining in pressure run rough till 0 then stalls. but will immediately start right bak up as soon as you turn the key off then to the run position you hear the pump and it starts right up every time. 

as far as the flow rate I assume it is fine because while pressure is up it runs fine will accelerate and you can drive it  

[Green Mesa XJ]

I’d try the swapping relays around to see if it’s the problem. Pressure dropping to 0 sound like it’s electrical in nature, possibly a bad pump . Did you use a bosh fuel pump?


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[ahmincha]

I did the relay switch. I am 80%sure it was Bosch. 

[Ωhm]

I've often wondered if using the fuel pump ballast resistor for a voltage drop could determine current flow thru the pump. This could just be wasted motion, but is simple to do. Hook VM across the ballast. Reading should be ≈3.0vdc under normal operation (at idle). Not sure what my question would be, but what does the VM do during the stall?

[ahmincha]

At this point I do believe it's electrical. My question is what has the ability to shut down the fuel pump. And what would reset when you restart it? If I pull the relay it does the exact same thing it runs in the until the gauge obviously hits zero

[HOrnbrod]

22 hours ago, ahmincha said:

fuel pump was replaced 1 yr ago

 

Do you know which pump was used for the replacement? Bosch. Airtex, etc.?

[ahmincha]

From what i can find out it is a carter pump 

[HOrnbrod]

7 minutes ago, ahmincha said:

From what i can find out it is a carter pump 

 

They don't have a good rep for longevity. I replaced my original Bosch 4637192 (NLA) with the replacement Bosch 69302 several years ago and it's still hanging tough. Not saying that's your problem, but all your startup circuitry seems to be working like it should.

[ahmincha]

Ok so i'm not sure if this is possible but I replaced the sender a few months back and the fuel level was not correct. Is it possible the computer would see empty on gauge and shut down power. Or the negative side my of been off of pump. 

I pulled sender put new pup in old sender which fuel sender works and truck seems fine ran a hour and a short drive. Will update in a few 

[HOrnbrod]

6 minutes ago, ahmincha said:

Is it possible the computer would see empty on gauge and shut down power. Or the negative side my of been off of pump.

 

Not possible.

[ahmincha]

I will update in a few days truck is not a daily driver.