1991 Mercury 135 V6 only firing on 3 and 5.

[bryanwess2000]

This motor came with a junk boat on a trailer I wanted. I tested compression
all 6 are 120-125lbs. I hooked up the wires on the switch boxes then
checked spark at 7/16'' and only 3 and 5 were firing. I swapped the # 1 and
5 coils and #1 was firing but then became intermittent # 5 didn't fire after
the swap. I tested the rectifier and it checked out ok. I tested all the coils
between the positive terminal and the plug boot and all read .90-.92 ohms
except #1 before i swapped them it read .82 ohms. The test between the
positive and negative read 0.0 on all.

The lady I bought the boat from said the stator was replaced due to hard
starting, it ran good for three weeks and developed the same problem. Her
mechanic said it needed another stator. It looks like the stator, at least one
switch box, and rectifier were replaced as well as a couple clip together
connections located between the coil packs. The coil packs and trigger
look original.

The boat doesn't have a kill switch lanyard which I thought was odd. The
motor would crank and run for maybe 10 secs occasionally so there may be
some weak spark on other cylinders. I need help on what to check next to
diagnose the problem, and any test equipment I might need. All I have is a
digital multimeter. I have a 1991 90hp that I could use the coils off of but
do not want to risk ruining them .

 

[j_martin]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

With compression like that there can't be much wrong with the engine. I have seen a stator wiped out by a bad top main bearing. If you pull the flywheel, you would see signs of contact on the stator.

I don't know what you're using for an ohmmeter, but the readings you say don't make much sense. Might be on a 1k scale, or internals in the meter might be bad.

It would be well worth your while to get a merc maintenance manual for that engine, and a DVA, or a dva adapter.

 

[Barnacle_Bill]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Those readings on the coils are good. They should be .81 - 1.09 ohms. But keep in mind they can still have other problems that won't show on a VOM.

 

[bryanwess2000]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

The meter is a GB instruments GDT-11, it's a cheap model digital multimeter
the measurements were with it set on 20k, on 2000 the coils read 910-920.
Wold any dva adapter work or should I buy a particular one?

When I commented on the compression readings looking good the lady that
owned it said " They should be,I had the motor rebuilt when I bought the
boat and I followed the mechanics instructions about running the engine
for a certain time at different speeds."

If I can get the motor working cheaply I'd like to mount it on my 19' starcraft
that has a 90hp.

I guess I can check the 135hp's coils on the 90hp, I think they have the
same coils and switch boxes. Both are 1991 models.

 

[j_martin]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

The meter is a GB instruments GDT-11, it's a cheap model digital multimeter
the measurements were with it set on 20k, on 2000 the coils read 910-920.
Wold any dva adapter work or should I buy a particular one?

When I commented on the compression readings looking good the lady that
owned it said " They should be,I had the motor rebuilt when I bought the
boat and I followed the mechanics instructions about running the engine
for a certain time at different speeds."

If I can get the motor working cheaply I'd like to mount it on my 19' starcraft
that has a 90hp.

I guess I can check the 135hp's coils on the 90hp, I think they have the
same coils and switch boxes. Both are 1991 models.

Pay attention to this statement:

Systematic diagnosis is the best way to limit the cost of replacement parts.

That said, it looks like there's been a bit of circular part destruction going on. Going at it systematically will get to the part or parts that are failing. Be careful about switching in one good part from a known good engine unless you know for sure what's going on. It's a known fact that the apparently good switchbox of a pair may have a failed bias circuit in it that will take out the replacement other.

Another item that is critical for both operation and longevity of ignition parts on this engine is good grounds.

A DVA is a peak storage and display meter. You can make an adapter that will work on a standard meter for about 5 bucks in parts. Any true DVA should work. They are easiest to read if they are an analog meter.

It sounds to me like you got a jewel, maybe with one missing ground strap and a bad ignition part that resulted.

 

[sschefer]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Since you are producing enough voltage to fire at least one coil and the coils that are firing are 1, 3, 5 the stator and trigger are working to at least some extent. The fact that 2, 4 and 6 are not firing leaves one thing in common and that is their switchbox. That switch boxes bias circuit could be affecting the switchbox for 1, 3 and 5. Always replace switchboxes on V6's in pairs.

 

[bryanwess2000]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Thanks for the help so far guys! Mr. J Martin could you tell me the parts to
get to make a DVA, I'll research it and I found one for $25 so that may be
the easier route since I'm not very savy with electronics. Also after thinking
about it, I was thinking it might be safer using the questionable coils off the
135 on my 90 to test them or could bad coils cause another problem with
the 90. I'll probably just wait till I get a DVA and check everything. The cheap
seloc manual that was given to me has some CDI electronics troubleshooting
procedures in it. I was going to swap the blue and red wires going to each
switch box and see if I get fire on the opposite bank of cylinders. The manual
says thats a way to tell if a switch box is bad. Unfortunately I think only
one switch box was replaced as one looks brand new and the other doesn't.

I think it's going to take a while to get this motor straight. It's got bolts
plugging tubing that go to the oil injection, some wires disconnected, etc.
I'm guessing the oil injection has been disabled, the lady I bought it from
gave me 10 gal. of premix gas. I'll try to post some pics of the motor soon.

 

[bryanwess2000]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

How can I tell if I have a 16amp or 40amp charging system? After looking up
parts for this motor I noticed both were made for this year/serial # motor.
The newer stator thats on the engine is a 16 amp model# 398-5454a34, but
after hearing the lady I purchased the boat from complaining about giving
the mechanic about $2000 and the motor still not running right makes me
not want to assume its the right one.

 

[Dukedog]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Need some pictures. Sounds like you may have a "sschefer" motor. All production motors went to 40 amp systems in '89/'90. So its been changed or tha whole powerhead may have been changed. PICTURES!!!!!!

 

[j_martin]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

How can I tell if I have a 16amp or 40amp charging system? After looking up
parts for this motor I noticed both were made for this year/serial # motor.
The newer stator thats on the engine is a 16 amp model# 398-5454a34, but
after hearing the lady I purchased the boat from complaining about giving
the mechanic about $2000 and the motor still not running right makes me
not want to assume its the right one.

Judging from your description, the "mechanic" is a hack. Oil injection can be removed, but it is neat, and doesn't destroy any parts.

Best hang it on a stand, get a manual, go at it like you're building it up from scratch, making sure every wire is in the right place, etc.

If the oil injection has been disconnected and the pump left in place, the best bet is to remove the pump, replace it with the proper block off plug, and clean up the rest of the removal. There's multiple threads on the subject here.

a 16 amp flywheel has a pattern of bolts in the hub. A stock 40 amp flywheel has the hub cast into it. A 40 amp flywheel over a 16 amp stator will do what you're saying happened. A hack "mechanic" could do that.

With pictures, we can tell you just exactly what you have.

hope it helps
John

 

[bryanwess2000]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Here's some pics. The only numbers I found on the block were 05 16 90
which I guess is a manufacture date. I couldn't find the serial number on
the powerhead anywhere and couldn't find a welch plug but the serial# on
the tag is 0D015203. The flywheel had # 74787 1B XK on the underside.
The switchboxes have different #'s 1 has 114-7778 the other 332-7778c
I know the stator was replaced, I just don't know if the right replacement
was used. Depending where you look, some sites say the 398-5454A34 goes
through 1991 others say 1988

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[bryanwess2000]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

One more, I'll get a pic of the top of the flywheel

 

[j_martin]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Need a picture of the top of the flywheel.

John

 

[j_martin]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

It's a 16 amp stator and a 16 amp rectifier on the switchbox mounting plate.

What's the flywheel?

Oil alert module is that box on the port side. Idle stabilizer is the box on top.

The switchboxes should be matched. Only a hack would put in different numbers.

 

[j_martin]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Need a starboard side carb/crankcase shot also.

John

 

[Dukedog]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

'90 model "fat" block. Supposed ta have a 40 amp. which is all they used after '88 on ALL 2.0,2.4 and 2.5 production motors. Someone has changed it. Like John says, need ta see tha flywheel...............
You need ta give both tha plastic boxes (oil and idle stablizer) tha "float test".

JAN John. Tha first 40 amp flywheels were "flex plate" style just like tha 16's only bigger. They were also red and/or black...................D

 

[j_martin]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

'90 model "fat" block. Supposed ta have a 40 amp. which is all they used after '88 on ALL 2.0,2.4 and 2.5 production motors. Someone has changed it. Like John says, need ta see tha flywheel...............

JAN John. Tha first 40 amp flywheels were "flex plate" style just like tha 16's only bigger. They were also red and/or black...................D

I know. You can tell by the height and the depth of the center hole. I don't think there were a lot of flex plate 40's though. I'm betting on the hack thinking he can convert to 16 amp with a rectifier and a stator.

Baffled about the extra red/white wire that's plugged off, though.

John

 

[Dukedog]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Tha 40 amp "flex plate" style is kinda kept quite by tha "hot rod" crowd. Think '89 and '90 were tha only years for it. Went away 'bout a year before tha water cooled reg. went away.
Yeah, tha wireing looks suspect. There is no red/white attached to tha switch box from tha stabilizer. Also looks like a white from bias goin' ta a red/white? Can't tell how tha regulator is wired................
Also looks ta be some kinda junk wired inta tha switch box goin' no tellin' where.....

 

[j_martin]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Tha 40 amp "flex plate" style is kinda kept quite by tha "hot rod" crowd. Think '89 and '90 were tha only years for it. Went away 'bout a year before tha water cooled reg. went away.
Yeah, tha wireing looks suspect. There is no red/white attached to tha switch box from tha stabilizer. Also looks like a white from bias goin' ta a red/white? Can't tell how tha regulator is wired................
Also looks ta be some kinda junk wired inta tha switch box goin' no tellin' where.....

Idle stabilizer miswired. Could 'splain some damage.

Could the junk be the lubalert harness? OMG, smoke time.

That engine is supposed to have the 40 amp wetback regulator on it.

Getting anxious to see the top of the flywheel.

John

 

[Dukedog]

Re: 1991 Mercury 135 V6 only firing on 3 and 5.

Idle stabilizer miswired. Could 'splain some damage.

Could the junk be the lubalert harness? OMG, smoke time.

john

Looks ta be MORE than enough for tha alarm..............