454 mag mpi chuggles/stalls

Fun Times

Fun Times

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tpenfield said:
You mentioned a new long block and the previous engine had the same issue. Did the intake manifold come from the old engine to the 'new' long block? (sorry if that was already discussed)
Click to expand...
This question on post 61 seemed to go unanswered...?
As in some reference, is item numbers 2 and 3 in place?, https://www.mercruiserparts.com/bam/subassemblydetail/37744147/28149300
dubs283 said:
Check the vacuum lines that connect to the fuel damper/regulator at the back of the fuel rail, port side of engine. There should be no fuel present in the line

That damper can fail and cause an overfueling/rich condition at idle. It will be evident by checking for fouled spark plugs

If this is indeed your cause, the damper is nla from merc and GM. In the past I've plugged the damper vacuum connection and the vacuum line at the damper to solve the issue
Click to expand...
Also post 13 needs attention.... Is there gas in the vacuum line / coming out of the fuel regulator? See hose A / 46, https://www.mercruiserparts.com/bam/subassemblydetail/37744147/28149300

Also in one of the videos above, the flame arrestor (#38) appears extremely black and dirty, have you cleaned it? ran the engine with it off and/or another one when you swapped plenums? Hope the engine isn't starving for air.

One sensor wasn't physically mentioned as being swapped out and tried but I suspect it was tried with the swapped out plenum is of the MAP sensor itself.
Have you tried a new/another used MAP by itself? I saw you unplugged it, etc. but have you inspected the MAP seal too (Item number 20)? They become compromised.
This may sound dumb but in the past I had found 2 bad MAP sensors by accidentally putting/resting my forearm down on the top of the (454/502 MPI) map sensor while the engine was running and found the particular issue the engine was having as the weight changed the engines behavior to normal... Try touching the MAP sensor...

Try swapping item number 17 just because, https://www.mercruiserparts.com/bam/subassemblydetail/37744137/28149300

Engine temp is reaching 154 degrees minimum? I saw 132.8 in one of the posts above not answered.

Item number 18 in place, https://www.mercruiserparts.com/bam/subassemblydetail/37744139/28149300
 
vroom ZOOM

vroom ZOOM

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468
Fun Times said:
This question on post 61 seemed to go unanswered...?
As in some reference, is item numbers 2 and 3 in place?, https://www.mercruiserparts.com/bam/subassemblydetail/37744147/28149300

Also post 13 needs attention.... Is there gas in the vacuum line / coming out of the fuel regulator? See hose A / 46, https://www.mercruiserparts.com/bam/subassemblydetail/37744147/28149300

Also in one of the videos above, the flame arrestor (#38) appears extremely black and dirty, have you cleaned it? ran the engine with it off and/or another one when you swapped plenums? Hope the engine isn't starving for air.

One sensor wasn't physically mentioned as being swapped out and tried but I suspect it was tried with the swapped out plenum is of the MAP sensor itself.
Have you tried a new/another used MAP by itself? I saw you unplugged it, etc. but have you inspected the MAP seal too (Item number 20)? They become compromised.
This may sound dumb but in the past I had found 2 bad MAP sensors by accidentally putting/resting my forearm down on the top of the (454/502 MPI) map sensor while the engine was running and found the particular issue the engine was having as the weight changed the engines behavior to normal... Try touching the MAP sensor...

Try swapping item number 17 just because, https://www.mercruiserparts.com/bam/subassemblydetail/37744137/28149300

Engine temp is reaching 154 degrees minimum? I saw 132.8 in one of the posts above not answered.

Item number 18 in place, https://www.mercruiserparts.com/bam/subassemblydetail/37744139/28149300
Click to expand...
Yes, the intake came from the old engine, and that is the only part I have not tried moving from the other engine, aside from the transmission. I will move it over today.

As for parts 2 and 3 there isnt even a hole for them in the intake.
No fuel in the vacuum line to the regulator.
Flame arrestor wise, the other engine runs with either or. I tried swapping them to no avail. I can see light through both so they should pass enough air to idle. If they were restricted I would see a very high vacuum as the engine starves for air. definitely not the case here.

Tried a new oem GM map sensor and tried the one from the other engine. Also tried swapping the distributor jumper harness.

That little connector (#18), where does it go? I do not recall seeing one.
 
vroom ZOOM

vroom ZOOM

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Weird update #102380703023!
Today, I swapped the intake manifold between both engines as that is the ONLY part I have not tried. Put it on and the engine started then quit. Unplugged the coolant sensor and it did much the same as before.

*Flashback from a couple of months ago*
I remembered another boat I was working on (just an old carby setup) with a pertronix module. On that thing, after installing a new module the timing was WAY out of wack. After turning the distributor it just randomly started loosing spark. Turned the dizzy back, and the spark came back (but really out of time). Without another thought, I moved each wire over one post and then the thing was close enough that I could time it up and make it run just fine.
*end of flashback*

Well, I decided to try this same thing here. Turned the dizzy way over so the rotor pointed at the next post, then moved the wires over. Also while messing around I realized I had unplugged the hose to the outboard tank I was running it from. Plugged it back in, purged the air from the rail, and tried to start it. It fired a couple of times but quit pretty soon as usual. I removed a spark plug, and I was OVERJOYED to see it soaked in fuel... This engine finally had too much fuel instead of not enough! I plugged the coolant sensor back in so the engine would stop dumping fuel in, and it just started.... and stayed running. No missing, no IAC hissing. just running.

I shut it off and started it again and it ran good again. I don't know if it will start tomorrow, as this engine has been a bunch of curveballs, but we are making progress.

My only theory here is that I somehow changed the time at which the injectors fire relative to the intake valve opening and that helps it take on more fuel... Which is kind of silly considering the sensor in the distributor does not know which cylinder is at TDC and this engine uses a batch fire system. super weird.

I am sitting here thinking if it was the intake manifold swap that did the trick or if it was the distributor...
 
alldodge

alldodge

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Glad to hear your running, but have issue with the cause
 
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