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454 mAG efi TWINS-ecm OR efi PROBLEM??

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Old 06-02-2003, 09:18 PM
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Question 454 mAG efi TWINS-ecm OR efi PROBLEM??

A real world brain drainer here. Twins, '97 454 Mag EFI's, .030 over, rebuilt, no hours. One engine is great but the other is like a alien from Mars!! idle speed is ok for both, but the port engine wanders, doesn't respond to throttle movement just off idle. Runs approx 400 rpm slower for any given throttle position. When throttle is advanced 1` click- no change in rpm... 2nd click the engine may accelerate to 1600 rpm & then slow down almost to idle again. EGT is higher on the port engine & reaches dangerous levels @ 3000 rpm even under no load. (see chart).
All readings taken with a Mercruiser scan tool & duplicated on both engines. No codes are ever recorded other than the "checksum" number which means nothing to me......
Computers have been returned to Arizona Speed for checking as there seem to be timing issues on the port engine also. Even though the timing says it is at 28* advanced per a timing light on the crank, the scan tool says only 18-20.1* advanced..... (starboard says 28*) but 3000 rpm timing is a matched 40.1*.
If the distributor is turned ever so slightly at 2000 rpm the timing goes straight to 40* or more!!

HELP!! EFI Wizard needed here ( many of these same indications were there before the rebuild also). Distributor gears are new & shafts tight. ?????????
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Old 06-02-2003, 09:36 PM
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we try to attach again...
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Old 06-03-2003, 03:03 AM
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have you checked the fuel pressure? Sounds like fuel starvation.

On the timing; did you put the engine into service mode when setting the initial timing to 8 degrees? The scantool and the ECM assumes 8 degrees of initial timing when displaying the ignition advance. If the initial advance was something else the ECM and scantool will show a false value.
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Old 06-03-2003, 10:22 AM
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fuel pressure is 45# at idle, increasing to 55# at full boost. Injectors are clean, two fuel filters (before & after Aeromotive A2000 pumps).
Yes, base timing was set in "service mode". The base timing is holding as is the 28* if read on the crank, but the scan tool shows 18-10.1* & varying at 2000 rpm which it should not do. The second engine is steady at 28* indicated on the scan tool.
????????
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Old 06-03-2003, 10:47 AM
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Tried swapping the ECMs between the engines?
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Old 06-03-2003, 01:31 PM
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I sent the ecm's back to Arizona Speed to check them out. No I did not swap them.... yet!! That's next..after the IAC's are tested and reset.
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Old 06-03-2003, 04:18 PM
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I donīt know what the ignition curve is supposed to look like on a blown engine but 40 degrees advance at 3000 rpm and above is definitely too much on the standard MPI engines. They usually are around 30 degrees in the 3000-5000 range. Also ,in 2000 rpm area, if the ECM thinks the advance is something different than it really is (18-10 instead of 28) it may do all kinds of funny things in trying to find the optimum advance. It may explain the hunting .
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Old 06-03-2003, 05:17 PM
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Another thought; If the ECM thinks the advance is something different than it really is in one part of the rpm range but you have a match in another part , the SW must be screwed up.
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Old 06-03-2003, 06:48 PM
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all good ideas to do first, you might also hook your engine up to a vacuum gauge, compare to two engines, this will let you know if you have any cam- are valve related problems, should be smooth and steady, if the needle is bouncing something is up, also spray carb cleaner are use propane to check for vac. leaks, around the intake, lower and upper, injectors, and throttle body, might also take a look at the spark plugs, I know you dont have any hours on it but its worth a look, let us know, also check your knock sensor's for damage
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Old 06-03-2003, 10:17 PM
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I guess I should have added that this engine did exactly the same things before the rebuild, I just did not have a scan tool at the time AND I was dumb enough to think it was normal as my other engine had a dead cylinder in it.... I was trying to "limp" thru the summer/fall last year with a "semi-working" boat.....
then the cold came, did the rebuilds & didn't start them until I got the cast off my leg in the middle of May.... it's hard to launch a boat with a cast on!!
Since the problem was there before, it seems unlikely to be a vacuum leak... but that is an idea to look into.

I will first reset the venturi plates to identical openings and reset the IAC sensor to the same initial voltage as the good engine.... therefore starting a "new" baseline of reference after the computers are verified by Arizona Speed (they got them this afternoon). I am learning, but it is hard to find "marine" mechanics that REALLY know what they are doing around here.....
so I am looking for the OSO expert help desk!!
Good ideas, but keep it coming.... especially about the timing variation @2000 rpm & the EGT trouble..... see the "bad" engine consumption is higher, so it is not lean & should be actually cooler EGT not hotter!!
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