b2.6 liter stumbles on acceleration any1 know Y?

The beast runs!!

sigh... but there is white smoke coming from the tailpipe.

Looks like the fog rolled in covering the houses in the afternoon.

I think I have to change the headgasket now.

A continuity tester won't beep when connected to an undamaged resistor. They only beep on short circuit conditions.

Bear in mind that to test a component accurately it must be removed from the board, or at the very least have one lead lifted. Otherwise your test meter(s) will see other components on the board too so the results will represent those components connected together in a system and it may not be possible to determine which of the components has failed.

Does anyone know the function of the upper clutch switch, mine is broke so I unplugged it thinking that at least it would not tell the ECU that the clutch is depressed.

That upper clutch switch is used to tell the computer when the clutch is engaged. It's used in conjunction with the neutral switch to determine when the engine is under load.

Clutch engaged + tranny in neutral = no load
Clutch disengaged + tranny in gear = no load
Clultch engaged + tranny in gear = engine under load

The ECM will then allow additional bypass air (it bypasses the throttle via the IAC/Bypass Air Control Valve) to the engine depending on many other conditions (several other inputs to the ECM.) One of the scenarios when it adds air is when you are at idle (in gear/clutch engaged.) This allows the truck to maintain the same idle speed as you are idling out of the driveway or down the road.

It will also add air when decelerating with the throttle at idle. If the clutch or neutral switch is bad, you my get some stumbling on deceleration.

If you have a factory injected truck and the clutch switch is unplugged, then the ECM will think it's in gear 100% of the time. In this scenario, when you are at a stop light, as soon as you put the transmission in gear, you will get a very slight increase in idle speed.

If the switch fails and creates continuity with the pedal released (clutch engaged), then that would make the computer think the engine is never in gear. Each condition would cause drivability issues.

According to the factory manual, the carbureted trucks trucks have a clutch switch that works in reverse to the injected trucks. With the clutch pedal released, you should have continuity across the switch. Depressed, you should not.

So one thing to keep in mind is that if you convert a carb truck to factory EFI, you may need to swap out the clutch switch.

I posted some info and test procedures of the switches on this thread:

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I have a factory injected B2200, help me understand this... if my idle raises when I put it in gear then my Neutral switch is bad?? and can cause issues? or is it normal for it to rise when putting it in gear?

I have had a stumble for all 10 years of having my B, *only with a cold engine* Idles perfectly all the time but during throttle tip in (idle, neutral, clutch pedal up) and also when gassing into the next gear after shifting, stumbles for a second and jolts back to life... all the sensors (under the hood) check out fine, plus once the engine is warm it runs like a champ. Could this be the culprit?

Thanks.

EDIT: NO, the Neutral switch is good, the clutch switch is bad. If either clutch or neutral switch is bad, you will have issues. And NO, It's not normal for the idle to increase just because you put it in gear. I have spoken to people who insist that it is because their truck as been doing since they bought it. But that doesn't make it normal. It just means that the Clutch switch was bad when they bought the truck.

It can and will cause drivability issues. Been there, done that. However, I'm not 100% sure that all of your issues are caused by the clutch switch. I think you may have something else going on too since you have a difference in warm and cold operation. But I would start with the clutch switch and make sure that's it's working as it should since I know of no other reason the idle would increase just because you shifted from neutral to a gear.

How much does the idle increase when you put it in gear, anyway?

Here is a quick and easy way to test out your switch and idle issue. On an injected truck, when you depress the clutch, the switch should make continuity - just like a brake switch. So rather than taking the switch out and trying to test it with a multi-meter, you can just unplug the connecter and put a jumper wire across it. This will tell the computer that you have depressed the clutch.

If your truck has cruise control, then you may have two connecters going to the switch - one for the ECM and one for the cruise computer. In that case, I would jumper both. Now start the truck and see if there is any change in idle when you put it in and out of gear. I wouldn't necessarily go driving it that way was the computer will think that the truck is no engaged. You're just trying to find out if this switch was causing your idle issue.

Also, check the condition of the "bumper" or "Stopper" pad on the clutch pedal. The switch will slowly wear a depression in the middle of the pad and it may be enough so that it is not completely closing the switch (i.e., the switch is in perfect condition.) If yours has a depression in it, you can try taping a penny over the pad to make sure it fully closes the switch.

Here is a shot of the pad...



Yes, I know the stopper is missing for the lower switch - I was in the process of replacing it when I decided to take the picture.





And here is the switch itself. This is for a B2600i. You might double-check the p/n for your truck before you replace it. And of course, make sure that it is in fact bad first. It might just need to be adjusted.

My idle only raises 100-200 RPM when I put it in gear.

I'm sure there are other problems with it but it has been doing this for 10 years and 2 different 2.2 engines so I think it will be fine. I will test out the switch at the pedal and tranny this weekend... Oh and no cruise control.

Thanks guys!

I've seen it do 200 or a little more, but most of the time, it is less than 100 rpm increase - maybe only 50 so it's hardly noticeable unless you are closely watching the tach.

Idling up in and of itself is not a big deal when sitting still and certainly won't cause you any problems. But if it is bad, and you do correct it, it will improve the drivability.

I'll bet your tranny switch is just fine - afterall, that is the only thing that is changing when you put it in gear.

Let us know what you find out!

Any info on how to actually test the tranny switch - I never even THOUGHT of these switches as controlling the ECU like that!