BillR

I need some more suggestions on what to look for.
Recap: I just had my motors (Merc 575SCi) rebuilt by Joey Griffin. All in all they run 150% GREAT. Start right up, idle well and run very well. The computers were sent to Mark in LA to get them to not be so rich and to raise the rev limiter to 5600.

Here is the problem:
While at idle, if I shift into reverse (sometimes forward) the motor will either stall or almost stall and drop to 300-400 rpm then surge up to 1100ish, and then settle down and run fine until maybe I shift again. When it does stall, it will re-start immediately. Also when flushing on the hose I try to run it @ 1400 rpm, but instead it will Roll, lope, surge until I move the throttle. This does not happen ALL the time. Only happens at the worse possible time. Vacuum is steady the whole time too.

Took the boat back to J. Griffin and he checked and adjusted the IAC. IAC base timing is supposed to be 15, it was at 36 on both motors. He adjusted them to 22 (both motors) and that gave the best recovery. He confirmed the thottle plates are not sticking. The adjustments he made didn't really change anything. So, he also sent the computers back again to Mark in LA and had him increase timing (not sure how much) and increase idle to 900.
Now the problem is WORSE. The motor will stall almost every time. Also, now the problem motor does not idle at 900 like the other motor. It is around 750-800 and just doesn't sound (very subtle difference) as smooth as the other motor. (The idle diff could also be the tach too)
ONE NOTE: When the motor is still "cold" and not totally up to temp, there is no problem, shifts 100% fine. It "may" drop rpms a tad, but recovers fine.

I am not tech, but it sounds like a computer PROGRAM issue.?? My thoughts:
Before rebuild, motors ran 100% fine. Nothing was done to throttle bodies during rebuild - other than removing them. After rebuild, J. Griffin water tested the boat with no issues mentioned. THEN the computers were sent off to have the rev limiter raised and leaned out as Merc runs them real rich. Computers installed by me. First time out, problem as mentioned above. Took boat back - IAC adjusted and computers sent to have idle raised and timing increased. Computers installed by me again, now the problem is much more pronounced and as mentioned above, the idle on the motor did not go up. (yes computers were swapped side to side also)


Someone here should be able to help. I really DON'T want to tow the boat back to Joey. I do have a freind who is a Merc tech, and will have him look at it later this week. I spoke with him about it, he wants to check some things, but no ideas came to mind.
Thanks in advance for all responses.

US1 Fountain

Do they use interupters on drives other than Alphas?

GOODT

on a lot of high hp and blower setups they do

customryder

ck ground wires

800XCR

Did someone tell Mark what the problem was or to simply increase the timing. There are some other parameters that he can change to help the situation described. He also needs to know where your base timing is set.

Another possible issue is misadjustment of the throttle cable and or tps.

Give Mark a call, he'll take care of you.

BillR

No shift interupters. plus that wouldn't explain the engine rolling @ 1200ish RPM.

Not 100% sure what Joey Griffin told Mark to do program wise. I did speak to Mark before he upped the idle and timing. Told him what it was doing. He then said he'd call Joey Griffin back and talk to him before doing the program.

I "assume" Joey Griffin checked all parameters when the boat was back down there to correct this issue. I also "assume" the only thing he found was the IAC adjustment. I was there with him the whole time and the only thing he adjusted / commented on was the IAC.
He expected to see on of the throttle plates slightly stuck open, but that was not the case.

I also just ordered a new IAC and throttle position sensor - just to be on the safe side.

Anyone have a computer for a Merc 575SCi that is not being used? I'd love to try it just to see if the problem gets resolved. All expenses paid!!

BillR

Update:
Just spoke to Mark. Very helpful and knowlegable. (Thanks Mark)
Joey Griffin was also at Mark's shop getting a motor dialed in, so they both conversed about the issue.
Mark & Joey think that one (or more) of the injectors could be at fault causing a lean condition. I have also ordered a set of injectors and will see if that helps. On the top on my injectors are these #'s 25170301-ACR and opposite of it is 4051-GM.
Is this a GM part #?



I also emailed Scott Buteyn from Merc Racing (I know him) and he sent back this:

If I remember correctly you have a dual IAC kit installed. To check for this remove your flame arrester. Standing in front of your engines looking down at the throttle bodies a one IAC system will have an IAC on the front throttle body. This will be about a 1 1/2" to 2" round item located at about 1:00 - 2:00 with a three wire connector. A dual engine IAC will have one also on the rear with a Y harness connecting the two. If you dont have a dual IAC, this would help.
PCM cal is different base on being a 1 IAC system or a 2 IAC system. I'm not sure who Mark in LA is but make sure the cal is appropriate for the number of IAC's. Check with a feeler gauge the throttle plate openings on both front and rear plates. They should be close to even and that should be around .012". Both plate adjustments are located at 6:30 position on the side of the throttle body. It is a torques type screw. The front throttle
body comes from us with the hole siliconed. The rear throttle body has a welch plug in it. Use a small drill (1/8" or less) to drill the welch plug. Then use a 5/16" bit. This will allow to get a torques bit in to adjust the throttle plate. To help matters you may find that if the rear plate is open more then the front it will help. The combined average should be around .012". So you could set the rear at .013" and the front at .011".
This throttle plate adjustment is only a starting point. Final test is using a Mercury scan tool or a Renda tool to set the IAC position electronically while running the engine. Quiz Griffin on how he set the IAC position. Make sure he put the boat in the water. The only way to set IAC is as follows: Have boat in water with propellers and boat tied to the pier. Allow engines to warm up (above(140 degrees) Shift engines into forward gear with throttle all the way back. (make sure the throttle cables are adjusted correctly) Watch for the IAC count to maintain a stable position. If higher that 20 open the plates, if between 0-8 close the plates. Shift the engine out of gear and them back into gear a couple of times allowing time to watch the IAC count stay in the 8-20 area each time. Then throttle up slightly in gear and back down to make sure once again each time the IAC returns to the 8-20 range. Check that the IAC valve is not carboned up. I have seen where the IAC has carboned the shaft. The IAC is held in with a couple, I think 7/16" head bolts. The IAC has a metal shaft with a plunger on the end. Made sure this shaft is clean. Wipe off with engine solvent or equivalent