1998 7.4L MPI Stalling

Getaway

Well-Known Member
Oct 13, 2010
1,077
Bay City, Michigan
Boat Info
1998 290DA Sundancer
Lowrance electronics, Fishhawk, Scotty Downriggers
BoatWheels Tri-Axle Trailer
Engines
Single big block 454 MPI Mercruiser engine and Bravo III outdrive.
I searched and could not find where this had been addressed in the past.

I have the engine stated in the topic. Mercruiser 7.4L MPI, 1998 vintage, Bravo III outdrive - 1998 290DA.

Runs perfect, however, when above dead idle, if you pull the throttle quickly to neutral or up against the neutral detent (but still in gear), it periodically will stall.

It's like the motor can't recover (idle wise) from bumping the ignition interrupt for shifting from forward into neutral.

It seems, the computer idles it down too low or the recovery time is too long when getting into the ignition interrupt from a higher idle point. If this makes sense..

If I'm at dead idle (just bumped in gear), no problem at all. In and out of gear for docking is great. But if I'm up at 900-1000 r's and pull it quickly down to dead idle or into neutral, she quits.

It will always quickly restart. If I'm careful and shift slowly, no problem. It's that quick neutral pull that causes this issue.

I've already changed TPS, IAC, Fuel Pump, Fuel pressure regulator and a few other things. The engine actually runs phenomenal other than this little annoyance. I'm being told by a mechanic that this is a typical problem and "they all do this". Well, I'm not buying it. There are probably 50 of these engines in our marina and I'm the only one having to restart when I approach my dock...LOL.

Any thoughts? I'm thinking there must be an ECM update or something that corrects this..?? Maybe I can make an adjustment mechanically to prevent this?

Thank you all in advance.
 
One thing is for sure, that combo does not have an ignition interrupt. Can we assume that you have had a complete tune up, wires cap and plugs ?
 
One thing is for sure, that combo does not have an ignition interrupt. Can we assume that you have had a complete tune up, wires cap and plugs ?

Yes. Complete tune up has been done including wires, cap, rotor and plugs.

Did not realize it doesn't have the ignition interrupt. Thanks for the clarification.
 
You're right to second guess that comment of "they all do this"... They only "do this" when things aren't right. That engine should run very smoothly with nice, clean shifts.

Correct - no shift interrupt on the B3. Different type of gear set, doesn't need it.

In addition to the above (which is probably the most common cause), if you're still having issues after cleaning, put a fuel pressure gauge on it. You mentioned you changed a bunch of things, but before you spend more money changes things on a whim, do some testing. Monitor the fuel pressure as you shift - especially when the issue is happening.
 
Had something similar going on before I replace my injectors. You should have it scanned to see what the ecm is showing for your IAC count. That ecm function can fail on the mefi-3
 
Check and clean throttle body and throttle plate.

Had it scanned, no codes, checks fine.

Fuel pressure is perfect 38 psi and steady. Bought a gauge and that is how I found the fuel pressure regulator was faulty. New pump and regulator fixed everything but this little glitch. Was 28 psi and fluctuating, but now steady.

Tech Mitch, can you explain your comment a little more in-depth? Have not addressed the throttle body yet...

Captainjeh, I guess misery loves company.LOL!!
 
Had it scanned, no codes, checks fine.

Fuel pressure is perfect 38 psi and steady. Bought a gauge and that is how I found the fuel pressure regulator was faulty. New pump and regulator fixed everything but this little glitch. Was 28 psi and fluctuating, but now steady.

Tech Mitch, can you explain your comment a little more in-depth? Have not addressed the throttle body yet...

Captainjeh, I guess misery loves company. LOL!!

Couldn't quickly find a picture of yours but this how clean it should be inside the throttle body especially around the edges of the throttle plate itself. After it's clean, remove ALL power to the ecm for about 10 mins before restarting.
https://shop.advanceautoparts.com/p...GRZxjYcGPTV5UuO0WYxoCJH0QAvD_BwE&gclsrc=aw.ds
 
Couldn't quickly find a picture of yours but this how clean it should be inside the throttle body especially around the edges of the throttle plate itself. After it's clean, remove ALL power to the ecm for about 10 mins before restarting.
https://shop.advanceautoparts.com/p...GRZxjYcGPTV5UuO0WYxoCJH0QAvD_BwE&gclsrc=aw.ds

Thanks! I’ll get into the TB and Check that all out. Ran some of the Merc Quickcleen through it a few times to try and clean the fuel system. Didn’t help much.
 
Got it!!!!!!

The previous owner had some work done with the shift cable that runs from the engine back through the out drive. The threaded end was stripped and not allowing alignment of the shift pattern.

When my service guy pulled the engine to do the shift pin repair/replace, he discovered the shift cable threads were stripped out and the cable was not secured into the bracket. :rolleyes:

The shift cable was replaced and now she shifts PERFECTLY!!! No more stalling or stiff throttle. YES!!
 

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