wiring issues with PCM controlling fuel pump....

bvk

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Ok, looking for some help here.

Long story short, I've been trying to solve hard starting issues on the viper on and off the last couple years. I have changed fuel, fuel filters, and spent $300 getting the injectors fully serviced and balanced.

It's a common thing for them, which essentially boils down to the fuel pump not running for long enough to fully pressurize the fuel system before you crank. The PCM energizes the pump for 1 second (by connecting ground to the pump relay) before it cuts out due to no engine rotation being detected from the crankshaft position sensor.

For whatever reason the fuel pressure reg, the screen or the pump just don't quite get it done in time. works fine when its running. annoying as ****, you have to keep priming it and then it goes. I want it to prime for longer.

There is a fix, it involves using an ELK-960 delay timer, ( https://www.elkproducts.com/product-catalog/elk-960-delay-timer-module ) a small circuit board, and hooking it up at the back fuse/relay box in the boot to extend the inital prime time by a few seconds. I couldnt get to said relay because the ******* that owned the car had a sub box PERMANENTLY INSTALLED in front of it. This resulted in me dismantaling the rear of the car (splash guards, rear bumper) to try and see it it was bolted on. Nope, said ******* just drilled the bottom plywood piece of the box into the fiberglass then glued/made the box around it. Had to rip it (with screws) out, so now i CAN get to the rear box. Lots of wasted hours.

before doing this i ****** around and tried to make the delay timer work at the PCM. I failed, and in doing so I seem to have stopped the PCM from connecting the ground to the fuel pump and energizing it. I confirmed this, if i just connect that wire to ground the fuel pump runs with the start/run circuit and car is fine.

However, I do want that safety feature such that if it gets crashed and the engine stops, the fuel pump stops running and passengers have a better chance of not being fireballed to death.

I'm trying to figure out if there is a way to use another 960 or similar to essentially replicate the safety feature, tap into the crankshaft position sensor wire (output ~5V, enough for the 960 module) but I don't think I can do it with just one, or maybe i need a seperate product.

here's what I think needs to happen:

- initial start/run power energizes fuel pump, but uses a timer such that if no rotation is detected within.... say 7 seconds (this is configurable on the 960) it cuts it off
- if rotation is detected (cranking or running) it keeps it on, but either a loss of signal from the crankshaft sensor OR no power from the start/run circuit it stops.

i THINK its something like example 9 on this sheet for the 960. https://www.elkproducts.com/_literature_63602/ELK-960_Instructions

I'm just not a car electrician and am scratching my head a bit. I'll keep noodling. Will draw some pictures and update if anyone is keen or able to help...
 
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bvk

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i think i figured it out. Two delay timers both set to provide the ground to the fuel pump module.

first one triggers to start/run and goes for like 6-10 seconds, only on initial power up.

second one configured to free run with trigger from cam sensor. When engine stops, cam sensor stops, it opens.

I believe that mimics the PCM safety feature behavior that shuts off fuel pump with no engine rotation (based on cam sensor) even if start/run is energized, and it gives me 7-10 seconds of fuel pump priming time rather than the 1 second fail time.

amirite
 
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bvk

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no i was wrong

its the crank position sensor not the cam that it runs off, and that doesn't give a steady output, more of a waveform but something like .2 to 2v when cranking.

so i need something that can take that and convert it to a steady +12v signal that I can use as a trigger that determines engine rotation. pulsed to steady 12v output. something like that, i dunno
 
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bvk

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actually, here is a better question that I hope someone can help me with.

Why would the PCM stop providing that ground to activate the fuel pump module? When I ground that out and start the car it runs fine, no codes etc. I have the service manuals, and all they tell you is the paragraph about how the PCM achieves fuel pump module control by providing the ground to the relay. No info on how to diagnose or what to do when this stops. wiring diagrams all just point to the PCM, pin 19 on connector C1 or C3.

Is it a PCM issue? cannot see any other obvious things - all fuses are ok, and everything works as long as I ground out that one pin for the PCM.

should I take it to dodge, I really don't know what to do, other than to go down the path I am and essentially make a little circuit to replicate the function. That seems do-able and really simple for someone with the know how, or if you're me, a few hours of figuring basic electronics shit out that I haven't thought about for 20 years.
 
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Steve-Indy

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Sorry for your troubles. Should we assume that you have a Gen I Viper? If so, it has long been known that with time said model develops a leak down of fuel pressure. The day to day, noninvasive solution is to turn on the key, allow pump to pressurize the system turn key off and repeat for two more cycles, then start. One solution offered over 10 years ago was a check valve that was soon abandoned. Next solution was a timer on pump as I recall. Search threads herd written on the issue by "Tom, F & L, GoR"...his work MAY save you some time.
 
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bvk

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thanks for the response. It's a Gen II GTS.
I've searched this issue on here, been dealing with it for a while, and doing that very day-to-day solution. I'm just sick of doing that, and I do want to sell the car eventually. The ELK-960 timer solution was one I found on this site. Due to a confluence of factors (mostly the irreversable and idiotic sub box install that blocked access to the rear fuse block put in by previous owner) I ended up ballsing up the install and the result was this PCM issue I am now trying to solve.

It's like I took 5 steps backwards, and now have taken 1 or 2 steps back towards square zero. Pretty standard effort for me unfortunately, I'm one of those do it 3 times then do it right people.
 
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bvk

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found a place that I can send the PCM to, if I can just get that back to working then i can do the regular ELK 960 fix and move on. I want to strangle the idiot who owned this car before me though and though it was a good idea to PERMANENTLY INSTALL a sub box in front of the rear fuse/relay panel. by screwing the bottom plywood piece of the box into the fiberglass then building the box around it. sheesh people
 
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