IH MV404 gasoline engine misfire -- help!

[Elliot Naess]

I have gotten the carburetor jetting sorted out, but my 1981 MV404
still fails smog check. It puts out too much hydrocarbons at 2500
RPM. The source of the problem seems clear enough: the #1 cylinder
is not firing properly. It doesn't show up on the scope, but when the
analyzer cuts out each cylinder, the #1 does not drop any RPM.
Of course, we verified this the old way also by pulling the plug wire off;
no RPM drop. So I've been driving around on a 7-cylinder engine -- well
a 7 1/2, or so.

We switched the plug with another; the problem stayed on #1 cyl.
The plug wire measures 10.000 ohms, just like the others. The inside
of the distributor cap looks good. Compression is 120, just like
the others.

What da heck??

Could the ignition system be failing to fire one cylinder properly? It is
an electronic distributor. There is a "star wheel" where the points cam
would be on an older unit.

How about the governor system? I have no idea how that works. There
is a little electronic box on the firewall that says "electronic governor
control", with three wires. What does it do? Does it pull the carburetor
back or does it kill spark?

Help! What are we overlooking?

 

[Elliot Naess]

Pulled the valve cover; no broken spring. Ran the engine with cover off;
normal valve movements and good oil flow on rockers.

????

 

[Griff-SKO]

Have you looked at the contacts of your distributor cap? Even though it is electronic, it still has a rotor button that translates the spark to the idividual wires. If the contact is burnt / broken, it may not fire properly, or if there is a crack in the distributor cap on / near the #1 cylinder tower, it could cause such a problem. (I had that happen on one of my POVs a long time ago, the distributor cap tower for that cylinder was the culprit.) Good luck!

 

[Elliot Naess]

The cap looks good inside, but you are the second guy to tell me that a
cap can be bad even though it looks good to the naked eye, so tomorrow
I'm going to NAPA for a cap and rotor. And plug wires while I'm at it.

I was hesitant to invest in cap, rotor and wires if the problem was a flat
lobe on the cam! But now that I know the valves move OK, it's time to
go back to the ignition system. Thanks for the input!

 

[the_experience03]

If you get it to fire and it still fails, go get yourself a used MSD6AL or similar sparkbox off eBay. You'd be amazed what a difference the hotter spark can make. It would appear that the RPM range they test you at is low enough that you would still benefit from the multiple spark events from a box too.

x2 on the cap, rotor, and wires. I go through probably 2 sets per year on my toyota. Even though they look great, I can feel the difference with my seat of the pants dyno and in my mileage.

 

[Elliot Naess]

Two sets of ignition parts per year on your car?! Wow! Well, I sure don't
doubt it, because I know I can feel my car runs MUCH better after I
change the oil! I guess I'm re-learning how important these things are --
mechanical things thrive on maintenance. (As do human things, but that's
a different bulletin board! ;-))

And I have heard good things about the MSD units for years, so that's
probably a good idea all around. (MSD stands for Multiple Spark Discharge.)

A friend suggested I might have a mouse nest in the intake port. Not
entirely impossible, since the bus sat for two years at the bus barn
before I bought it. But what are the odds?!

Thanks for the input! A pile of ignition goodies coming up!

 

[Steve-SKO]

A friend suggested I might have a mouse nest in the intake port. Not
entirely impossible, since the bus sat for two years at the bus barn
before I bought it. But what are the odds?!

Actually that happens more often than you would think. They will also make homes in exhaust pipes and fill you cylinder with crud through the exhaust valve.

I have a vintage car in my garage that was parked only a couple of months and when I started it up last week a bunch of walnuts shot out of the exhaust pipe because some critter was hording them in there.

 

[the_experience03]

The only "reasonable" solution I can see to the mouse nest problem is a 14-71 supercharger with a mechanical injection and huge injecter hat coming out of the hood. Show those mice what boost really means.

 

[Elliot Naess]

You mean like this little doohickey on my street roadster?

All right, it's fake. Full of radiator tank and carbonator and air filter and flat cap disturbinator.

Back on topic: Do any of you know anything about the electronic ignition
on my 1981 MV404? A friend has a 1983 SV392 from the same school
district and it has POINTS! So I'm wondering if my electronic is
aftermarket. It has three wires; the white one goes elsewhere and the
engine runs without it.

Good attitude, '03! It might come to that!

 

[the_experience03]

The white wire is probably a tach signal wire. Ever notice if the tach stops when you unhook it? I won't claim to know specifics of that ignition, but they're all pretty similar. The only way you could be having a problem with spark on one cylinder that I can reasonably see is the cap and rotor combination since this is the only place in the system where the spark energy gets defined for being for a specific cylinder. A coil would have to be pretty intelligent to skip every 8th spark event

I saw in you post the you tried different wires with the same problem. Have you physically tested for spark on the #8 terminal? Take a nice long wire and put it on the #8 terminal with a plug in there and gorund it out to something while you crank it. Yes, it's possible to get shocked. Yes, they sell the correct tool for this, but it costs money and I'm cheap. Finding out if you're actually getting spark to that cylinder will go a long ways to solving this problem.

 

[Elliot Naess]

Right, the white wire is probably for the tach. The tach does not work, so...
(Anybody know what redline is supposed to be for a MV404?)

Let's see... It is the #1 cylinder I have trouble with. Oh yes, I have spark there --
ouch! But it seems like I have good spark some times and other times not.
Hard to say. We ran the "kill-one-cylinder-at-the-time" test on the scope and it
showed no RPM drop on #1 each time.

I think we are down to an invisible flaw in the cap as the most likely suspect.
(Or the mouse nest!) I'm going "to town" tomorrow (Sacramento) so I'll get parts
there. Rechecking the vacuum advance, I found that it leaks a little bit, so I'll
replace that too.

I can get a MSD 6A "box" right here in Clearlake for $200,40 out the door.
I suppose that might "cover up for" various other weaknesses that might exist
in a 1981 engine.

Will be gone for a week. Appreciate any ideas you guys might have in the meantime!

 

[bdavis441]

I'm also a huge fan of the MSD 6A. It's one of those things that shows up more on the "seat of the pants dyno" than anywhere else. My 392 has a petronix aftermarket electronic ignition, seems to work fine.

 

[Jarlaxle]

Check the compression...I'd bet money #1 will have little or none.

 

[Elliot Naess]

Quoting myself:
Compression is 120, just like the others.
How much money did I win? :wink:
I'm home from a week on the road and I have bought $400 worth of
ignition parts, including a 6A. Stand clear!

 

[Griff-SKO]

. . . and I have bought $400 worth of ignition parts, including a 6A. Stand clear!

I know it will take longer to do it but, if you replace those ignition parts one at a time and check the result, you can determine exactly which component caused the problem, and I, for one, would like to know what the actual fix was. :?

 

[frank-id]

Wow all that money for ignition

Do they still make gas engines for buses??? I'm convinced that diesel is the only engine power. I'm gonna get a diesel powered lawn mower. Ahhh yes the smell of diesel on an early autum morning. The work is about to begin... Frank in Idaho.... no smog rules

 

[Steve-SKO]

My only diesel is my mower and yes the smell does make it more enjoyable!

 

[Elliot Naess]

The really funny part is spending $400 for ignition parts -- on a $250 bus! :shock:
Of course, I spent $2209.40 on tires!
Long term, the tires can go on a newer bus, and the "hot rod" ignition parts
on my street roadster or an other car. I consider this old gasser my
"practice bus", while I keep an eye out for a bargain on a 40 foot Bluebird TC2000
with diesel engine.
Now I need to get out there and work on it -- going on a trip Thursday!

 

[eggman-SKO]

$400 for ignition parts on an International Gasser?? Holy cow!! For that, you couldve had fuel injection. Question is, did that take care of your problem?

For some info on IH gassers and on some of the diesels, try http://www.binderbulletin.org

 

[the_experience03]

Re: Wow all that money for ignition

Do they still make gas engines for buses??? I'm convinced that diesel is the only engine power. I'm gonna get a diesel powered lawn mower. Ahhh yes the smell of diesel on an early autum morning. The work is about to begin... Frank in Idaho.... no smog rules

Ah..the smell of ether and the words of frustration on a cold morning when your lawn mower's block heater fails to start it.

As for the fuel injection...sure he could have had it, but that doesn't fix a weak spark if that was in fact the problem.

I know it's a long ways away from you, but the guy who does the bus sales at United Truck Body (where I bought mine) in Duluth came into our store a few days ago and said they have some real nice ones coming in. One is a 72 pass. TC2000 with a 5.9, air brakes, MT643 (IIRC), 4.44 ratio, and a host of other goodies. It was always stored in a heated bus barn. No block heater on that one and we're darn near in the tundra up here. Best part was the price...$2700....

You can try their site, but I'm not sure that it has been updated. Either way, don't pay attention to the prices. Mine was listed at $2000 and I paid $1250 without any negotiaion.

http://www.unitedtruckbody.com[/quote]