Mercruiaer 350 Timing jumping around. Low WOT

[fishngolf]

Ongoing issue with 94 mercruiser 350 5.7 EFI. Have low WOT approx 3100 RPM so switched out ignition control module back to original and wot jumps to 4000 but won’t idle smoothly. Took video of the scanner. Timing seems to be jumping all over at idle.
https://youtu.be/DysPJkdCak0


Serial 0F230168

 

[Bt Doctur]

do you have it in "base timing mode"

 

[muc]

Yes that’s normal for ECM controlled timing.

 

[Bt Doctur]

No you have to manually put it in base timing mode with the scanner and raise the throttle control to 1800 I believe.

 

[Bt Doctur]

1. Connect timing light to number 1 spark plug wire.



2. Start engine and run at 1300 rpm until it reaches normal operating temperature.



3. Stop engine and connect the scan tool or timing tool to the DLC connector on the EFI/MPI wiring harness. Depending on the production they will stick that DCL a few different places. But in most cases it is on the front top left of the engine as your facing it. If you do not have a timing tool or a scan tool, what you can do is jump pins A and B on the DLC together with a jumper wire or paper clip. Click this link below, this will bring up a picture of what I am talking about.

http://i.imgur.com/HBPIMG0.jpg



4. Start engine, allow rpm to stabilize.





NOTE: MEFI-1 models only, manually adjust remote control throttle lever to get 1200 engine







rpm.





NOTE: MEFI-2 and MEFI-3 models only, ECM will automatically adjust engine rpm to

approximately 1200 rpm when put in the service mode on a scan tool or when using the timing tool.

 

[alldodge]

When the motor is idling my guess is you can hear a rattle in the transmission. This would come from the motor is missing. The miss can be from the ignition, but can also be from cylinders not having same compression.

Also noticed the voltage is 13.5 (+/-) which should be one volt higher

 

[fishngolf]

I do receive error code 42 as far as codes go. I’ve had the ECM tested by OBD diagnostics which tested out good.

 

[alldodge]

Code 42 open or shorted Ignition circuit
I'm thinking bad ground

 

[QBhoy]

Should that TPS not have 5v to it ?

 

[QBhoy]

Or maybe I’m just used to the mpi. Does the efi have a TPS ?

 

[alldodge]

TPS should see 12V

 

[muc]

all EFI have a TPS
TPS uses the 5v reference
1/2 volt @ closed throttle is normal
Only thing out of the ordinary on the scan tool was low temp. Always have the engine up to operating temp when scanning.

This Malibu has had 2 long block's replaced under warranty. Guessing it has been rode hard.
Suggest check compression and read spark plugs.
Check ALL grounds and wiring.
Check total timing advance and while you have the timing light connected, shine it at the injectors while slowly advanceing the throttle up to about 2500rpm. Take a close look at the injector spray pattern.

 

[alldodge]

Woops, was the IAC that uses 12V

 

[fishngolf]

Interesting. How can you tell about the replacement engines?? ECM says 730 hours is that total or just on this block? Compression checks out now at 148-150 across the board. #8 was originally very low after it had been sitting a few years (stuck Rings). I checked all the grounds and cleaned everything up. No change.

 

[muc]

First engine failed right away and the replacement failed in 1999. It's in the warranty files. Only long blocks were replaced so ECM should be original to the boat. Edit... But I don't know for sure. To check that you would need to call MerCruiser with the ECM info to see if it's the right calibration loaded in it.

Have you checked fuel pressure and manifold pressure at W.O.T.? If so what are the numbers? Then recommend the items in my first post.

 

[fishngolf]

Haven’t checked the fuel pressure as with the different ignition control module rpm was able to get up to just about 4000 but didn’t idle well. Current ignition control module idles ok but only gets up to 3100 rpm or so. There’s no test port so I need the special tbi adapter and I don’t think it’s the fuel with the different ignition control modules obtaining different wot rpms. Checking the timing is beyond my abilities so I’ll have to take it in. Any shop recommendations in CT?

 

[Bt Doctur]

You put it base timing mode with the scan tool and point and shoot like a normal timing light
Go to a junk yard and acquire the 2 sections of fuel line tubing, with the schrader valve on it , join with a short piece of hose. remove fuel line from throttle body, screw in your end and screw the other end into the original fuel line. attach pressure gauge, your looking for 31-32 PSI

 

[muc]

I do receive error code 42 as far as codes go. I’ve had the ECM tested by OBD diagnostics which tested out good.

Sorry, I missed this last time.

Code 42 on your engine means that the ECM isn't able to take control of the timing.
There are only 3 possible problems that can cause this code.
1. Ignition module, Is the module from MerCruiser? Some aftermarket module's will have this problem.
2. Wires between ECM and module. Service manual #17 has a very clear and easy method for checking this, it does require a test light and VOM
3. ECM. I know you sent this out for testing, but did you tell them you had a code 42? Without that knowledge they probably wound't test that circuit ---- If they are even capable of testing for this code?

I'm in Minnesota so don't have any recommendations on a shop. other then it should be a MerCruiser dealer with a certified tech that will be the one working on your boat.

 

[kenny nunez]

When I first got my Donzi It had a lot of problems, after working through them the last thing it was doing was a rough idle and sometimes just stop. The TPS was the problem, since then it finally runs right.

 

[fishngolf]

I had replaced the TPS earlier this year hoping it would be that easy. Unfortunately the same issue persists. I also changed out the IAC while I was at it. Today I completely disconnected the perfect pass and just did a straight connection from throttle cable to control. Much smoother acceleration and I can now get up to about 3500 rpms. Ignition control module is really finicky. Even just moving the connection wires slightly at idle will cause the engine to die. There are two connections on the module a 4 pin and a 2 pin. Which is the ground so I can track it back through the harness?