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8.1 won't stay running.

Agreed but it just seems odd that it runs always for 4 seconds and shuts off. Seems a bad ground would be more intermittent. There are so many wires going in all directions it hard to even see where they go.
 
To me, with good fuel pressure, the logical thing is something is telling the injectors to turn off, or they are just doing it on their own. Is there a way in that rinda to tell for sure if the injectors are firing?
 
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You should be able to see the commanded pulse width....and a noid light on an injector should be able to verify it is triggering.

Best to check the wiring in the service manual to verify how the injectors are wired/triggered....most are in two banks on a V-8....
 
Remote fuel supply was simply pulling hose off of fuel tank and putting it in a 2 gallon fuel tank. We did not bypass low pressure pump.
 
Bt Doctor, am I following you correctly? Do you think this relay is turning on initally then shutting off after 4-5 seconds?
 
If your losing system power this relay controls the 12v ,it is activated by a ground from the ecm. Replace the relay and try again DISCONNECT THE BATTERY, locate the purple wire at pin 4 cut it and ground the end away from the ecm. This will cause the relay to remain energized as long as the battery is "on" so be careful.
That or a sensor is not seeing something with the engine running and telling the ecm to shut down, rpm feed, coil feed, cps feed, etc

Or if wish not to cut it, locate pin #87 in the relay and cut that wire and jump it to a 12v feed
th
 
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ecm`s control things by giving it a ground thru relays and such. your basically going to hot wire the system . If the motor now runs you have a ecm that is being told by a sensor to shut down or a ground lead that is a intermittent ground.

Sometime you wire in a panel light to a circuit .If the light stays on, that circuit is ok, if the light goes out, that the circuit that needs testing.Locate #87 hook a test light to it . Hook it to the ign coils 12v side , light on at start, light goes out ,an ign feed problem.
 
Ok, here's the latest. Starboard engine runs fine. Changed the map sensor side for side. No change. Still runs for 4 seconds, shuts off. If we pull plug on map sensor on port engine it runs fine. Doesn't matter if we use port or starboard map sensor. Thoughts?
 
So tonight we pulled and cleaned all sensor plugs, started engine with map plugged in. Ran for 5 seconds, shut off. Removed map sensor plug, ran for 5 min! Plugged map sensor back in and ran for 5 min by itself. Never shut off! Good news is it's running. Bad news is, I'm sure it's not "fixed". We ran it with scan tool and at idle we had 99.9% IAC duty cycle. Is that normal? I've read where that can get hot and start a fire. I see there is an IAC sensor and an IAC motor. Which one is the one that gets hot?
 
Doing a bit more research it appears the IAC should not be at 99.9%. someone on another site thinks that is wide open so too much air leaving a lean condition. Pulling map sensor causes a richer condition so it runs. We ran an IAC test with the scan tool but no matter how far we changed it(something like +/- 100% the engine didn't change rpm or sound. During that test should something change? We are now thinking bad IAC valve but we get not codes saying it's bad.
 
You're right, IAC should be maxed out at idle.....

Before condemning the IAC, I'd make sure the MAP sensor was somewhat accurate - The manual has a chart crossing the voltage produced with the vacuum applied.

I'm not familiar with the IAC test on a 555 ECU but i'd think the test would exercise the valve thru the entire cycle.....
 
I interpret 99.9% to be functionally equivalent to 100% .....

the exact value varies (& again, the 555 isn't my strong suit) based on engine's mechanical health and state of tune.....I'd expect 20-25% being a reasonable spot. Unfortunately, i don't have access to my manual set right now so can't see if there's a nominal value published....

It's always possible that the port the IAC regulates (for idle speed control) has a restriction in it....my theory is a clog would limit the air delivered, independent of the IAC valve setting requested, and wouldn't cause a code to be set....
 
that would be the best approach....and while you are there, you can get a baseline for the MAP and other sensors of interest....
 
Starboard engine runs good. We were able to cycle IAC valve with rhinda scan tool and it changed the idle on starboard side.we changed IAC's and we can still change idle in starbord side but not port so I'm assuming wiring is messed up to Port engine. But iac is only for idle, right? We can get it up to 2500-3000 but it hunts from 2230-2500. Is it possible that the low pressure pump has failed and it's only running on high pressure pump? Fuel pressure is fine. As well, when we tromp on the throttle it wants to die. Similar to a carbureted engine when accererator pump goes bad.
 
sammi said:
We did that! Problem stays with same engine!
Click to expand...
If you changed the ecm and the problem stayed with the engine and you cannot actuate the IAC with your scan tool....I would say you have a wiring harness issue. Problem is.... if the harness is bad.... there is no fixing it. You would replace it as a unit.

one more question
You ran the engine with the fuel pressure gauge attached out on the water under a load, what was the pressure while running?
 
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O2batsea. That is what we are wondering about supply pump. We can feel by hand it's doing something but who knows if it's pumping fuel. I'm thinking we have 2 problems. A fuel issue and a wiring issue when IAC won't activate.

We never got it out on the water but fuel pressure was good. 43 but I don't remember anymore.
 
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