Dead injector?

[1990dtgl98]

So here's the deal.


I bought a project 1999 searay 230br. Got it running decent after a bit of back and forth. I still have an issue with it not revving over 3600 rpm under load.


I replaced cap/rotor/coil/plugs and wires last season. Set base timing with a techmate.
Had to replace the fuel pump as I only had 20psi.
Now I have spark and good pressure at the rail.
However it still won't rev over 3600, and the hole shot pulling skiers/wakeboarders up still feels subpar.


So this weekend I did a spark test, pulling wires and seeing if it sounds different under load. #5 and #6 had no perceptible change.
I pulled some plugs before having to put the kids to bed and here's how they look.


Looks like #5 is dead. Could it just be an injector? I had so much with the cool fuel and am hoping it could just be the years of neglect? Plug doesn't smell gassy or look wet, like it was a clogged and spraying bad. Just looks like it hasn't been used.

Buy a set of 8 injectors and be done with it?

 

[achris]

Boat and engine are different manufacturers. They can even be different years (have a look at my boat!). When I say '1972 Bertram 20', do you immediately know what engine is in it? A car on the other hand, maybe. If I said '1999 Toyota Landcruiser', you'd think either 6 cylinder diesel or V8 petrol... See the difference? (but in this case you'd be wrong anyway, I have a 6.5L turbo V8 diesel.)

Please state, engine model, year and serial number... So far, all we know is it's a V-engine with injection...

Before you go throwing money in an effort to fix this thing, injectors are incredibly reliable. Over 20 years of working on injected engines, I have not had a single failed injector.

Chris...

 

[1990dtgl98]

My bad. Thought I added that.

1999 Mercruiser 7.4L L29. Serial 0L399641

I've only had 1 injector fail in anything I've worked on as well.

 

[achris]

If not an injector failure, then maybe something got passed the filter and is in the line (or in the injector itself)... ??? I know it's not easy to change those injectors, but swapping them to a different location might be a good diagnostic tool. (I just hate throwing money at things hoping something will stick)

Chris....

 

[dubs283]

Do a cylinder drop test to confirm issues with suspect cylinders. Then you can try an injector swap as suggested

 

[alldodge]

Drop cylinder test won't work on the L29 because it uses batch firing.

Its possible its a wiring issue
If you do buy injectors don't buy them from ebay, get them from Merc or GM

This is a 555 but shows how batch firing works. Your MEFI 2 will use different pins

 

[1990dtgl98]

If not an injector failure, then maybe something got passed the filter and is in the line (or in the injector itself)... ??? I know it's not easy to change those injectors, but swapping them to a different location might be a good diagnostic tool. (I just hate throwing money at things hoping something will stick)

Chris....

Usually i don't either.

However it did sit for 3 years. I replaced the fuel line, fuel filter, anti siphon and pickup, fuel pump and regulator after siphoning the tank and only getting 14 psi at idle with the old pump.

Now I get 34-36 at idle. Vacuum is a touch low to me at 14", but seeing that #5 plug with about 10 hours on it have zero signs of combustion makes me think something did get past the fuel filter (or something came off/rusted off and is clogging that injector.

I might re compression test that cylinder specifically, but the first thing I did when I bought it was a test, and I don't remember the exact numbers, but all were within spec and 10% of each other.

Don't remember any detonation, no knock or pulling spark according to the techmate. But maybe it bent an intake valve somewhere along the line on #5?

 

[dubs283]

Drop cylinder test won't work on the L29 because it uses batch firing.

Fully aware the 7.4 mpi mefi controlled engine uses batch fire.

I'm not suggesting pulling injector leads for the test but pulling plug wires from the cap which I know works and have used many times to isolate issues on these motors

 

[alldodge]

He did that see first post

 

[achris]

This is a 555 but shows how batch firing works. Your MEFI 2 will use different pins

I checked the serial number, it's MEFI3... But same, batch firing.

Chris.....

 

[dubs283]

He did that see first post

Got it, missed that part

#5 and #6 fire with separate circuits so driver/ecm issue isn't likely. Could be wiring, continuity test would show an issue if that's the case. If all checks out next step would be remove and test suspect injectors individually. Sitting for three years could have gunked them up and they need cleaning/flow testing or they have failed. Swapping positions with known good injectors/cylinders could show issues with suspect injectors

My guess is having injectors cleaned and flow tested is cheaper than replacing all 8

 

[Scott Danforth]

My guess is having injectors cleaned and flow tested is cheaper than replacing all 8

Yes

 

[todhunter]

My guess is having injectors cleaned and flow tested is cheaper than replacing all 8

Yes, my guy charges $100 to clean and flow test a set of 8 injectors.

 

[1990dtgl98]

So I'll try to do a play by play as I go.

Had some kid free time.

Took out the plugs.....have spark at each cylinder at the plug.

#5 and #6 cylinders Def don't have combustion.

 

[nola mike]

So I'll try to do a play by play as I go.

Had some kid free time.

Took out the plugs.....have spark at each cylinder at the plug.

#5 and #6 cylinders Def don't have combustion.

Don't know how easy it is to throw a noid light on the suspect injectors, but that would be my next move...
Or swap injectors.

 

[1990dtgl98]

Plenum needs to come off.

So will need gaskets. And a couple more hours.

 

[nola mike]

Plenum needs to come off.

So will need gaskets. And a couple more hours.

Yuck. Gross.

 

[1990dtgl98]

Compression test:

1- 160
2- 160
3- 150
4- 155
5- 158
6- 161
7- 151
8- 160

 

[1990dtgl98]

Injectors all ohm'd between 12.3 and 12.5
Power and pulse to all wire.
Pulled the rail and got 1 bank off so far. Injectors are all heavily clogged. Rail doesn't have any pieces in it.

Do I need to worry about the new injectors clogging or do you think the rust was a combo from sitting for so long and the fuel pump being bad (which I replaced)?

 

[Scott Danforth]

Send the injectors to be cleaned. Clean the fuel rails