I am still having some troubles with Baby Blue. Today we continued to have the rough running condition occasionally on start up. I also had a condition when coming back to idle where the RPMs would oscillate between 600-900RPM. Giving it a quick blip of the throttle would solve the oscillation.

I will be changing the fuel filter, checking all plugs and wires and check the connections for the sensors. I will also be cleaning the fuel water seperator.

If that doesn't work I am looking at getting a scan tool or even a data logging system to be able to log data whe nthe problem is occuring.

Any idea if VP uses OBD1 or OBD2

They use GM's ECM? Should be OBI II if it's even used...

Sounds like a possible dirty or worn throttle position switch.

SB, it's neither OBD1 or OBD2. Those terms refer to the automotive industry.

More than likely your problem is a dirty throttle body. Do you know how to clean it?

CNY: I thought the 8.1's used port injection? I could be wrong...

It does. The throttle body on a port fuel injection engine lets the air in.

When the throttle is closed, there is a small amount of air that enters the engine around the throttle plate. This is referred to as "minimum air rate". The minimum air rate is calculated into the calibration of each engine. The computer "fine tunes" this with the idle air control valve (IAC). Basically, there is a secret passageway around the throttle plate for additional air to get in. There is also an ugly valve monster in the passageway that the computer can control to change the amount of "bypass" air that gets into the engine. When the engine is cold, for example, more air is required for a higher idle speed. This is how it is accomplished, through the controlling of the valve monster.

What happens on many PFI engines is "coking" of the throttle body. Gas and oil vapors tend to build up in the area of the throttle body where the plate and bore are, after the engine is shut down. This alters the minimum air rate (reduces it), and the computer can detect through the engine speed sensor that the engine is going to stall, so it orders the IAC valve monster to back off and let more air in. Then it realizes that there is too high of an idle speed, and closes the bypass air down again. This will happen several times, hence the idle fluctuations, before it can find a happy medium.

The fix is simple - open the throttle all the way (ENGINE OFF, OF COURSE) and spray carb clean on a rag and clean the gunk in the bore and on the throttle valve edge. An old toothbrush helps too. Don't use any more carb clean than you have to, and be very careful about spraying carb clean into the throttle body (Superglue the straw into the nozzle first - the straw can blast off right into the engine). And that's it.

This should be part of your winterizing procedure on PFI (MPI or GSI) engines.

The old EFI engines (TBI or throttle body injection) do not have this problem.

Thanks for the info! Thanks!

Great info CNY. Hadn't thought about doing that in the boat. I have to clean the TB in my 5.3 powered Suburban about every 3 mos. when it develops a sticking (closed) throttle. Very annoying when the pedal is initially hard to push then breaks free and you lurch forward. So whenever it happens I spray the carb/TB cleaner in and all is good again.

Glad I have TBI then!

Thanks CNY. Shouldn't bee too hard since the arrestor is coming off anyway.

Couple questions for you.



Could this also be a cause of the rough idle on start up that smoothes out after about 30 seconds or should I be looking somewher else for that?

You mention supergluing the tube the the carb cleaner. Are you implying that I should spray carb cleaner into the throttle body? I thought that was a no-no since it can wash crap into it which will then cause the engine to ingest it.

They make both a carb cleaner and a throttle body cleaner. Does it actually matter which one I use?

I also found the port is called MEFI and there are versions 1-5b. I am going to talk to one of the local shop owners I know to see if I can borrow their scan tool.

I may still get a data logging set up if I continue to have issues, but they are a bit over $500 and I would prefer not to spend the money. But I would rather spend the money for the equipment than to pay $200-$300 for someone to tell me what is wrong.

RX,

What really is happening in your Burb is the minimum air rate adjusting screw and/or stop has worn a bit, allowing the throttle plate to sit too far into the bore. The very smallest amount of coking causes the sticky throttle, and in some cases, a clean throttle body will actually still stick because the plate is too far into the bore.

What I do on the 4.3L and the V8's is adjust the minimum air rate clockwise about an 1/8 of a turn in. The screw is a small Torx, T10 or T15 I think. An 1/8th turn isn't enough to upset the minimum air rate calibration.

It's hard to say whether your rough idle is due to a dirty throttle body or not. An idle searching or hunting on a PFI engine, especially on a cold start, is usually due to a dirty throttle body.

Boats are different than cars, in that the way a misfire or rough idle feels, because of the engine mounts.

For someone who has never cleaned a TB before, I don't recommend spraying carb clean directly into the throttle body because I am afraid of them spraying the entire can into the engine and hydrolocking it. Burning a small amount of carb clean and the gunk is not a concern, and throttle body cleaner is just marketing (you can use either carb clean or TB cleaner, it's basically the same stuff).

I don't know what kind of relationship you have with your dealer, but asking to borrow their scantool is "interesting". Obviously you didn't buy the boat there. I hope you know them REAL well..

The idle hunting actually happens when I come back to idle after running a bit. As soon as the baby goes down for the night I will pull the flame arrestor.

I have a pretty good relationship with the shop. In fact, they are getting out of boat work and I am going to try to score some of their specialty tools. If not, I found a place to get a data logging set up to get real time data from the ECM.

I'm not familiar with cleaning throttle bodies, but I get the hint of not spraying a can down there. I'll do it primarily with rag and see how it goes.


On a side note, what do you think about sea foam or deep creep to spray down while running to clean the intake. Just curious.

Every engine that I've ever taken apart has a "dirty" intake manifold. It doesn't bother anything and I don't recommend any induction-type cleaning other than TB cleaning.

Keep us posted!