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!

I took off the flame arrestor. There was a film, but nothing hard or crusty. The flame arrestor seemed pretty dirty and there is a sensor in it (MAT Sensor) so I don't know if it is cleanable like the one on my 5.0GXI was.

Couple of thoughts---

buy "throttle body cleaner" instead of carb cleaner. Does the same thing but leaves less residue and evaporates MUCH faster.

--about the 'valve monster' (I like that), aka the IAC (idle air control) valve--if you're TB is so dirty you need cleaner, it's possible that the IAC itself is sticking. They can be removed and cleaned, but I'd suggest a repair manual...

And remember our thread on dirty MAF sensors? That could cause many of your symptoms...

I will have to look into removing and cleaning. I have the EFI manual already and will hopefully have the engine maunal by next week.

I don't see a MAF sensor on the schematic.

Those sensors and valves are expensive. Makes me a little scared I might mess them up. Even the o-ring to take the IAC off is almost $14.

There are no MAF sensors on I/O boats, only MAP sensors.

SB, the amount of coking that causes problems is very small, and what you cleaned sounds like the normal build-up. I am not familiar with the flame arrestor on the 8.1L, but if it has a MAT sensor, can't you move it? I clean my flame arrestor in mineral spirits (parts washer). I don't think mineral spirits will hurt the sensor, but you have to be careful not to physically damage it, obviously.

GM IAC valves very rarely cause problems. Ford, on the other hand, has had problems with theirs on cars and trucks since, oh, the beginning of time.

I have cleaned probably over 1000 throttle bodies since the 80's using regular old spray carb clean. It works just fine.

SB, how many hours are on Baby Blue, and what type of spark plugs are in it (Delco Double Platnium or the old Delco MRxxyy)?
Did FLB ever have them changed?

I'm actually going to check the part # for the plugs tonight to see what they are. I did some research about a month ago and I found only one number and it was not a Delco #. I'm hoping these have a good number to cross-reference off of.

I tugged on the MAT sensor which is a temp sensor I guess. It will spin, but it doesn't come out. I will try to get a mirror and see if there is a clip on the inside. The flame arrestor is a wierd design geometrically so there is not much access.

Baby Blue has about 330 hours I believe off the top of my head. I don't know if they are the original plugs. FLB might have told me, but I don't remember at this point.

Glad to hear the GM IAC valves cause few problems. I think I will not touch it for now, but I will order the gasket so I have it if I need it in the future.

I happened to have Throttle Body Cleaner already so I used that. I only used a rag to prevent getting any in there. I did not spray any in the intake at all. I just sprayed it on the blue cotton paper towels and wiped out as far as I could reach in with my fingers.

I don't have the energy to deal with mineral spirits, but I think I will use some water and simple green to see if I can get it cleaner using a toothe brush from the outside. If I mess it up I have a new one on order already (almost $100)

My biggest problem is our longest boat trip of the year is next week and I don't want to have issues on the lake, nor do I want to cause damage by not fixing something. I'm up against a wall and we don't have local dealers that stock parts. Everything has to be ordered in.

Keep the questions and progress reports coming. I'll do my best to help, but it's tough to diagnose over the internet.

Thanks for all your help. Hopefully I can take it out on Saturday and see how she runs after checking over everything. I think I will be ordering the data logging system tomorrow and it will be here by Friday. It would be nice if they put a check engine light in the boat. At least you would know if a code was present.

May have found the (a) problem.

Actually found 3 issues while digging around the motor tonight. I don't know if they are the cause of the issues.

1.) The spark plugs were installed in May of last year. They are RS12PYP which is the same plug that my 5.0GXI used and I thought the plugs were different plugs. So, perhaps the wrong plugs. Perhaps not.

2.) One of the plugs was not even finger tight. There was not much soot around the plug so it doesn't seem to have been leaking bad, but it definitely could have caused some issues.

3.) Whoever did the wiring on the motor was having a bad day. The harness is not in the proper position creating an issue with one of the plugs on the ECM. First, the plug is pulled to the side which could be a problem. Bigger than that is that because of this, the insulation was damaged on at least one wire.

4.) There was something else I found, but I cannot remember at the moment.

So, I need to determine the right plug. If these are wrong change them for the right ones and retorque all of them. Take apart some of the hoses on the engine and reposition the wiring harness. I also need to seal those wires with liquid electric tape to ensure there is no moisture or corrosion issues.

The good news is that through this inspection I found the serpentine belt to be just about worn out. So I have a new one on order so I can change that out.

B.O.A.T.?

More like 1/2 B.O.A.T right now. But it could go to full B.O.A.R. Hopefully not.

I didn't know EFI boats DIDN'T use MAF sensors, good to know!