7.4 MPI No start

[ynnad]

I have been trying to get my 7.4MPI to start after about a year storage in Florida.

I filled it and treated the fuel (ran it to get it all the way through the system) before I stored it. It was running fine when I put it away.

When I first tried to start it, it wouldn't crank. Turned out to be corroded ground at the engine. (sits on a hoist, but we have salty to brackish water that seems to cause everything to corrode).

After I cleaned the ground it cranked, but no fire. I had the fuel tank pumped dry, put in fresh fuel and a new filter. Again no start, not even a pop.

I pulled the plugs and found them from black and sooty to some with rust!

I pulled the distributor cap and found all the terminals had white corrosion as did the rotor.

New plugs, cap and rotor...now it fires (pops) on the 1,3,5,7 bank but not on the 2,4,6,8 bank..It turns like it wants to start, but it will not catch and run.


I have never had this problem before even when it was stored without treating the fuel...I do have fuel in the system. I checked at the schrader valve on the fuel rail and it squirts fuel.

I am not sharp on the MPI system, so I don't know if I have stuck or plugged injectors...it does seem odd that only one bank will fire.

Any experience on this?

Thanks in advance,

Dan

 

[Chris E]

a couple of things - first - the battery you have should be 1000 amp. the efi system needs a full 12 volts just to power up. if you battery is ok, then my thought is the gizmo (i'm sorry i can't remember the name) it's in the distributor - oh yeah - ignition sensor. 2 wires come off it. they are prone to failure. other than that, make sure it is in neutral, and make sure the kill cord connection is good - i'm all about looking at simple stuff first.

 

[ynnad]

Chris thanks...

I thought about the sensor in the distributor, screws were really corroded. Back to the Mercruiser dealer for another big $ bill..

I'll give it a try.


Dan

 

[powerstroker]

isnt there a inline fuse that goes to the starter on those? mine was blown once and i coundnt figure out why it wouldnt start but i checked that out and it was blown!

 

[daren34]

sorry to ask but did you take all the plug wires off at the same time or change them out one at a time

you need to test spark on a few different wires to eliminate bad wires or a bad cap

sounds like maybe a few plug wires out of order

you would think the treated fuel would keep the injectors clean

the plugs were black because of weak fire to the plugs

i dought it is the module in the dist

usually works or it don't not half way

good luck daren

pull number one plug out and bring the motor up to top dead center with your
finger in the spark plug hole when the air blows your finger out start looking
for the timing marks
helps to have a freind or a remote start button

pull the cap and make shure it is puinted at number one wire

if you bring it up on the exaust stroke for number one the rotor will point to number 6 wire

the rotor should be clocked at 11:00 at tdc

you can use a timing light on number one while cranking and see if it hits the timing indicator to verify it is in the right position on the cap then the
rest of them follow 1-8-4-3-6-5-7-2 clockwise

good luck daren

 

[ynnad]

Daren 34 and Powerstroker

Thanks for the input.

I checked the fuse at the starter and it is fine.

When I changed the distributor cap, I transferred one wire at a time.

I verified that all the wires were good, and made sure #1 cyl was up at TDC, as well as the distributor on #1 for proper timing.

The dealer doesn't stock the sensor (not that I wanted to pay $116). Like you, they said it works or it doesn't...wouldn't give me firing on only some cylinders.

The tech at the dealer said sounds like weak spark...just like you said, black plugs means weak spark.

They suspected the coil was going bad, or lack of adequate voltage to the coil was producing poor spark.

When I pulled the new plugs after my most recent attempt, they were wet with fuel...no fire.

Maybe my earlier cranking to try to start it with the badly corroded cap and bad plugs hurt the coil...?

I believe that they can check out the coil if I take it in...so that would help the diagnosis.

New coil not in stock, but available on Monday.

I have cleaned all grounds and all positive connections between the batteries, starter, and feeds to the coil.

Possibly a poor ground somewhere in the system?

Since this thing has an ECU, is there something that the dealer can plug into it to help diagnosis?

Thanks again

Dan

 

[kingsbiship]

Check your 'kill' switch!

 

[daren34]

try the screwdiver test at the coil have someone cramk it over with the
blade grounded slowly move away from the tower should have a blue spark and jump at least a 1/2 inch gap

i preferr a wood handle or you can use a 12 volt tist light with the lead to ground

check the coil wire also no more than 7 ohm's per foot

the ecm on boats is about 1/4 as smart as the one in most cars

it will store codes but no scanner hookups

seems strange that you had spark before and not now

a coil is the last thing i would suspect

good luck

 

[ynnad]

Thanks again for your ideas...

I checked the kill switch first and it works fine...

I did get a spark off the coil, but not a big fat one.

At the suggestion of a local friend I have been checking all the grounds and hot leads for corrosion. With several folks saying my spark is not hot enough to light the fire, I am looking for anything that will cause a drain or poor juice to the system.

He said that bad grounds figure in most of the electrical problems on boats with ECU, especially around salt water.

Something about poor grounds suck up all the juice (especially when cranking) and make the coil, ECU, and other things see much less than the required voltage.

He told about a time when he had a laptop plugged into the cigar lighter and into the ECU on a boat that was not running right.

With the laptop, it worked fine, but when he unplugged the laptop, the problem came back...the power and ground for the laptop through the cigar lighter were providing just enough extra to the ECU to overcome a bad system ground...

They found a badly corroded crimped terminal (not corroded at the connection, but the wires in the crimp were corroded)...this fixed it.

I found a similar situation late today on the main hot wires for the engine harness off the starter (at the connection to the big fuse at the starter on my MPI).

While the connection is clean, the wires were all corroded in the crimp and I wouldn't have thought twice about it unless he had tipped me off.

Tomorrow I'll get a new terminal and see if that does it.

Dan

 

[happy]

rust on any spark plug is a sign of bad news, no fuel additive or any thing else will help this situation.. run a compression check and post a few pics of your manifolds and risers.. while it happens, its rare that your computer is at fault. the basic abc's will answer these questions air? how much compression on each cyl, a spark check, and how much fuel pressure your running.. (with a guage)

unfortunate as it sounds, you probably need a valve job at minimum, and new exhaust

 

[ynnad]

Happy

Thanks for the guidance, I was hoping it was something simple (never the case).

Fuel Psi is 40. Manifolds and risers were replaced less than 10 hours ago (not long before I stored it).

It was running fine when I put it away about a year ago. It sat on a lift the entire time.

The bad news is that the compression check shows 4 bad cylinders!

With the heavy salt environment, the fluctuating temperatures, I can only guess that salt condensation caused several valves to freeze up...

#4,6,8 are all 25-60 lbs compression...#5 is zero!

I know I need to pull it apart to see what gave up the ghost, but was just curious since you pegged valve job...

I have heard that 7.4 MPI had a reversion issue, but like I said it ran fine when I shut it down.

Thanks

Dan

 

[happy]

Hey Dan, glad you found the problem, I'm sorry it has to be the costly side, some days i feel like the grim reaper..
The key on this one was rust on the plugs, bring a red flag up the pole so fast it'll make your head spin.. what happened here is she reverted the last time she ran, and had water in her when you shut her down. then sat for a year. Please really consider a full freshen up on the block too.. your rings may be rusty too, and cause you more trouble in the near future.

Now some really important information here.. If your manifolds were purchased from a mecruiser dealer, and you have the reciept, and its at or under 1 year get the dealer you bought them from to see if merc will warranty the engine for you due to manifold failure.. (they will, i've seen it more than once, and they will probably have to get the rep involved) I hope this is the case, and you can let the merc dealer fix your boat and you can enjoy margaritas or your favorite beveage.

if you let me know what type of exhaust you have or are able send me some pics so we can figure out how to solve the reversion problem before it happens again on a new engine..

 

[ynnad]

Happy

Unfortunately I didn't get the new manifolds from a Mercruiser dealer. I want to pull them to see if and where they were leaking.

The old manifolds I replaced were leaking into the bilge. I only noticed because I kept seeing anti-freeze coolant from the closed cooling system in the bilge. I finally felt the bottom of the manifolds weeping anti-freeze coolant through the cast iron...maybe the damage was done by the old manifolds and the engine died after the new ones went on?

I have seen on other blogs (various boat brands that used Mercruiser 7.4 MPI) that there were known reversion problems with 7.4 MPI even without leaky manifolds or risers.

Something about cam overlap causing exhaust water to get sucked back into the ports when running at idle. Not enough exhaust velocity to make it all go out the pipe.

I know Vinny has said that cams are critical on boats to avoid this situation, that and dumping the water out as far back from the manifold as possible. I always assumed that stock Mercruisers did not have this issue until I read those blogs.

I plan to pull it all apart, but I want to get it on the trailer first. I don't relish working on the lift.

I have already been looking at new/rebuilt marine long blocks vs. just taking it all down and rebuilding it, including the bottom end.

Pricey stuff!

Thanks again

Dan

 

[daren34]

i would call whoever you got the manifolds from to get thier response before i tore it down

sorry for the bad news though

good luck resolving this

daren

 

[happy]

vinny is absolutly correct about cams and revesrion, and years ago he wrote a post on this site that was out of this world. and i dont know if his typing got any better but he used to chicken peck, and had to take him quite a while to type that hole thing out.. more power to you vin.. (and that post would be before rep power) and i'll give you some when i figure that out.

I'm not so sure that this is the problem in this case, as mercruiser does think about thier product, and doesn't wish this problem on any engine. Now lets assume that the boat came from the factory the way you have it.. no engine swaps, no upgrades, bone stock.. How many hours are on the engine? how long did the old exhaust leak? Does this vessel have a history of reversion?? if when and how was this handled? what is the base measurment from static water to riser height? how does the boat sit in the lift? ((lean forward lean aft)) do you know the previous maintenance on the boat?? is it verifiable??

There are other reasons how water gets in the engine besides the cam, ei bad manifold, cracked block, lifting incorrectly, engine misfire, or a weak cylinder to mention some of them.. and as you had mentioned, the problem may have happened with your old manifolds, and not the new, it just took it a bit to give up the ghost. it would be nice to know some if not all of these answers before running a new engine, to ensure that proper steps are taken to not let this happen again. Once again i'm assuming your manifolds are fresh water cooled, and the risers are sea water cooled.

typically what happens is (on a fwc system) is the manifolds themselves do not corrode away, however, electrolosis eats the joint between the exhaust manifold and the riser away, soon one see's weeps in this area and are often ignored or painted over because the engine is still running.. it is my experience if its leaking on the outside, its leaking on the inside.. now i've pulled thousands apart, and there are no traces of water on the inside, but have pitted valves because the water is being burned off when it hits the valves, in this situation the valve is taking a beating, and there is no visual proof of why its happening. (other than we know what it is, we've fixed this before) now putting new manifolds on before the engine goes caput??? does that help? does it slow things down?? depends

i'd venture to say 85% of the engines go down in this type situation after running what the owners say is fine all day.. untill they go back some time later to find they wont start. so right now i have to bet that you don't have a cam problem, you have a problem thats not found yet..

there are countless boats out there that get run hard and put up wet and never cared for, and sold and now the new owner has tons of problems,

I'd reccomend this, rebuild your engine, since it turns over, more than likeley you have mimimal lower end damge, and from what i've seen and heard from that way florida is not that busy right now, so your chances of getting a better labor deal are quite good.

labor wise at a shop you should be looking at 6 hrs engine removal and install, 10 hrs for dress and undress the engine. plus macine shop charges.. now thats gonna vary, you should pull out of a shop down there for less than 5k easy

hope that helped