MPI troubleshooting help

alk

alk

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After 12 years with a carbed 350 in my boat, I finally dropped back in a replacement for the original motor, a 7.4 mpi.

I saw the replacement motor start right up and run fine with a test harness when the motor was sitting on a palette. Got it into my boat last week, finished hooking everything up this morning- but can't get it to start.

It will crank. And when first hitting the key it sounds like it's about to fire, but wont. I was thinking fuel, because it does sound so close to starting. But thinking it may be spark, I put a timing light on it - to see if it was flashing.

When I turn the key and motor starts cranking, I get ONE flash from the timing light. Doesn't matter how long I leave the starter cranking, don't get a second strobe.

When I lay off the starter for a second, and try again right away, I do NOT get a timing light flash on next attempt. But if I wait about 5-6 seconds, until after I hear a relay located on the back of the coil 'click', now I do get the one flash when cranking and the cylinder fires, but again continuing to crank never get another spark to the cylinder I'm hooked up to.

I thought I had everything wired correctly, with all my grounds good. If I had no crank, or no spark ever - I would assume I missed something on the hookup. But it's like something is tripping to protect the motor by shutting of spark, a second or two after I start cranking.

love the whole MPI / ECM system when it's working, but really in the dark trying to troubleshoot this. Anybody have any ideas who these things work? thanks.
 
Alk,

Guess as you know you need to determine if it is "spark" or "fuel". Try pulling a spark plug to see if it is wet (smells like you have fuel). I am not sure if you can do this, but maybe you can shoot some ether(SP) into the throttle body? Wait to hear from others before you do that. To check for spark, I assume you can pull a spark plug wire and use the old screwdriver deal to check for spark. Unfortunately, I am not knowledgeable on MPI, but just shooting out some ideas.

Walter
 
I can pull a plug, but the fact that the timing light flashes at me as the motor is spinning, but only one time, has me pretty sure I will also see one spark.

My guess is that there is some kind of shutoff in these ignitions that kills the spark if it senses some other condition - and I am for some reason sensing this condition. But just a guess; trying to research online, but looking for an expert as I'm not finding much.
 
Only one flash on the timing light makes it a spark issue. Not being adept with all this new technology (I still have a rotary dial cell phone) methinks either a wiring issue or the ECM-if you have one-needs looked at. The relay clicking would be the first thing to look at-what controls that? Keep us updated on what you find.
 
Could the clicking relay be related to lower voltage getting to the ECM during cranking, shutting it down and removing voltage from devices the ECM controls like ignition and fuel pumps, injectors,etc. ? Starter causing excess voltage drop with high current
? Maybe replace the on-engine fuse for the ECM even if it looks & tests OK?

Or possibly the ECM is not detecting signal from the CKP/crank position sensor ? But if that were the case I wonder why you get the one spark. Speaking of which , if you put the timing light pickup on the coil wire instead of a plug wire ( if that's where you tested) , do you see any add'l flashes at all?

Does the oil pressure gauge move up at all when cranking? Oil level rechecked on proper dipstick for that application and good after oil has circulated slightly ( filling remote filter and lines)? Is battery fully charged and testing Ok? Any lanyard kill sswitch key in place?

On a tangential note, the jump from 5/7L carbed to 7.4L MPI offers a lot of potential for fun . Just wondering if you upgraded transmission ( if I/B) to handle the big jump in torque, and increased exhaust hose , muffler and transom exhaust ports's size to handle the increased air flow to prevent excess back pressure? None of that would be causing the 1 spark predicament.

A marine diagnostic scan device with proper adapter... could ...save a lot of guessing , even to help rule out many suspects. Sooner or later (like now), with an MPI engine you are likely going to want to invest in one and the ignition diagnostic manual. That said , I'm not sure how much data an attempt at a scan will provide with ony 1 spark while cranking.

Do you have a service manual with wiring diagram yet?

What is the back-story on this 7.4L MPI? Year/model/rated hp/ser.# if Merc. ( for parts check)?
Is a new turnkey engine , or used/rebuilt/remanned?? What all did you have to add or wire up?
Does it have the Delco EST distributor , or flat-top cap on a "high voltage switch" that looks just like a distributor, or distributorless ignition?

Disclaimer: Justaboater
 
If you have not, check the wiring again looking for bad connections. Were any sensors used on the test rig removed and replaced with your own?
 
I saw the replacement motor start right up and run fine with a test harness when the motor was sitting on a palette. Got it into my boat last week, finished hooking everything up this morning- but can't get it to start.

Was the test harness wired the same as you harness plug, do you have a serial number of the replacement motor?
 
rainy day today, didn't have much chance to look at anything - but I did look around again for loose wires, burnt or missing fuses - and didn't find anything. Trying to start today, same thing. Turn on the key and the fuel pump cycles, plenty of fuel pressure as evidenced by the fuel which sprayed all over me when I checked the shrader valve at end of fuel rail. With timing light inductor on coil wire I get 5-8 quick flashes when motor starts cranking, really sound like it's going to fire but then spark cuts out. Wait 5-10 seconds, relay clicks, fuel pump cycles on - and ready for another 5-8 sparks.

The motor has the standard merc 10(?) pin plug. The shop I bought the motor from had a key-switch he plugged into the harness, and cables from the battery to back of starter and block. That was it. I must have broke or blown something when I installed the motor - I have same harness, plugs right in. I know this boat is wired / fuel plumbed / geared, etc correctly for this motor - as it's the identical setup I had when I bought the boat new in 1999. When I put the small block in in 2006, all I changed was the props.

Motor serial number is 0L028306. This was a 'running take out' used motor from some guy who had it in a Formula that he barely used. He died, boat wasn't worth much because vinyl, canvas,and everythign else was very worn - but motor ran great. Scan tool showed about 450 hours when we ran it in the shop.

i have the clymer and seloc books, I think boatfix.com has the merc manuals online still? The factory manuals are great, but they operate under the assumption you have all of the merc diagnostic tools, which I don't.

I am leaning towards pulling the motor back out, and taking it back to the shop I bought it from. Not ideal, but he has all of the scan tools ( which are freaking expensive) -- so hopefully he can get it running on the pallet again. He did tell me I could bring it back if I had any problems. Or maybe I will tow the boat up there, and see if he can fix it still in the boat ( that probably won't be free though). Left them a message Saturday, hopefully will be able to talk to them Monday.

The smallblock I pulled still runs fine - I picked up a straight inboard ski boat this winter that had a blown motor. Plan was to put the SBC into the ski boat, and then get a rat motor back into the bowrider. But summer is coming, worst case, I will just drop the carbed 350 back in, and forget about the ski boat until I get the 454 straight.
 
The culprit is in here somewhere :D :

http://www.marineengine.com/parts/mercury_marine_parts/sn/0L028306/4542067LS/2705_60

I once had an MPI engine that wouldn't start but cranked fine. Turned out there was a very slight, very hard to discern bend in one of the fuel pump relay connector pins . Once that was straightened and connector reconnected, the fuel pump energized and the engine started right away when key was turned.
So you might check each connector that was apart and look realllly carefully for anything that might be amiss.

You could try temporarily disconnecting the OP switch leads too.

The #94070 Rinda Techmate Pro kit is about $500 with one adapter, straight from Rinda. Rinda at least used to be happy to swap out the usually included 94005 adapter ( for GM MEFI ignitions ) for the 94006 adapter which I ...think... would be appropriate for your Mercruiser EFI (MPI) engine's diagnostic connector ( but check with Rinda if interested in a purchase.)

http://www.rinda.com/acro/TechMate_Pro_Specs.pdf

What would one visit to the shop for them to scan likely cost you? And you can't keep the shop tech with you on the boat. Well, not for $500, right?
 
If it boils down to taking it to the mechanic, take it in the boat. Otherwise you could wind up right back here after the test.
 
the engine plug should be a match to yours. Did the PO/mechanic use a harness or just jumper wires on the motor plug?
 
he had a 'homemade' harness.
 
found a local shop that let me rent their scan tool - showing two errors code 42 - EST System Gounded. and something about low oil pressure telltale has been set. Which I don't think tells me anythign useful.

I am going to pull the motor back out, and see if I can get it running on the stand again. The access in this boat is so tight that it's almost less work to pull the motor first just to change the starter.
 
Can you start it with the harness used when on the stand while the motor is still in the boat?
 
Taking it to a knowledgeable mechanic and having him troubleshoot the problem HAS to be cheaper than pulling the engine...putting in on a stand and trying to see if anything is wrong. You need the problem sourced and fixed in your boat-not on a stand. Then again, if you have more money than yanno what to do with, I have a boat that could use a cash infusion.
 
It wasn't my harness, belonged to the shop where I bought the motor - several hours from home. But I did order a male 10 point merc plug yesterday that I can use to build my own harness. I think I have an extra tach, temp and oil pressure gauge somewhere in my garage - so I should be able to rig up a pretty cool little harness - just need to find an ignition switch , or I suppose a toggle and pushbutton.

Finding a knowledgeable mechanic ( or even a clueless one) willing to look at a boat around here, this time of year, is pretty much not possible. At the Mercruiser shop close to my house, where I go for a lot of parts, I looked in the shop yesterday, they had so many boats in there it was hard for them to even walk around. I asked them how backed up they were in service as I needed some work done - he just laughed. If I leave my boat tomorrow, no guarantee they would be able to look at it before end of JULY! There were two other decent shops in my area - one of them closed a few years ago when they leveled the whole block to put in a Courtyard Marriott, and the other stopped doing service and only sells parts now. Most of the marinas near the beach stopped doing service years ago - only a few left and they are expensive and busy

Trying to pull off a double engine swap on the cheap, starting in late April, was not the wisest move I ever made -- but no regrets yet.

The benefit of pulling the motor is that if I ( or the guy I bought it from) can't get it running right again on the pallet -- I drop the small block back in, and I'm ready to go boating. If it does run right, I will know that the problem is on the boat, not the motor. I know, not the most efficient way to diagnose a problem- but considering I can't even see the front or back of the motor once it's in, and I couldn't afford to pay someone competent to fix this thing even in the impossible event I found someone willing to look at it -- if the new harness I make doesn't get it started, motor is probably coming out one evening later this week.

Pulling the motor is surprisingly easy - and since I haven't aligned it or put the drive back on yet, now would be the time to do it.

Getting a little worried by the 42 fault code it's throwing, my limited online research says to replace the ignition control module and/or ECM. If I have to replace both of them, that's about more than I paid for the motor - so I may go another direction.
 
Start simple and cheap. If the boat has a kill switch lanyard, ensure it is attached. I stranded myself for an hour once with your symptoms because the lanyard end was halfway off the kill switch.
 
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