Okay, first off this isn't on my Dakota, but lots of knowledgeable old school guys here, so a quick question.

I have a GMC Syclone, that seems to have developed a dead miss on one of the cylinders. It's been modified over the years with an MSD coil pack and standalone EFI setup.

First thought is obviously pull the plugs and check each one for spark. Well, to do so on the passenger side, I have to take nearly half the engine apart...all the turbo/intake/down tubes run in this area. Second thought is to check the Fuel injectors with a Noid light, but that only tells you there's a signal, correct? Doesn't tell you if an injector is plugged.

So, is there some magic test, to first determine if I should be looking at spark vs fuel? I do have a wideband A/F gauge, and I've noticed after it goes closed loop it wants to run lean around 15 to 16 A/F...that tells me maybe it's a bad injector? If it were no spark, I'd have too much fuel and the A/F should be lower. If it were a bad spark, wouldn't I be washing the cylinder and have either fuel vapor leaving the exhaust or a strong smell of fuel. I have neither. I tried pulling one spark plug off the distributor at a time, but the engine is so strong, damn thing will run on only 4 cylinders (I even pulled 2 at a time), so it's hard to tell. I don't hear any significant worse stumble or RPM drop when removing each plug from the distributor.

Some of you old school guys, school me in your magic ways.

 

If your A/F guage is showing 15-16 it sounds like it is starving for fuel.
Do you have any way to check the stand alone efi and see if it is trying to add fuel?
Can you access the injector plugs easily ?
If so, could you unplug one at a time and see if you get a change ?
FWIW I too, suspect a bad injector.

 

I can probably get to the injectors easier than the plugs...but since it was hard to tell any difference pulling plug wires I assumed pulling injectors would be the same result.

 

Put a brand new set of plugs in.

Drive it about 200-300 miles.

Pull the plugs and read them. Be SURE to label where each plug came from per cylinder.

(Does the stand alone EFI not have a monitor port? Any way to datalog?)

RwP

 

lol...I know I can do that...was trying to narrow it down to spark because it's probably a 4 hour job to remove the plugs.

 

Quote:

Originally Posted by robertmee

I can probably get to the injectors easier than the plugs...but since it was hard to tell any difference pulling plug wires I assumed pulling injectors would be the same result.

I would think, that if it is an injector not firing properly, you would notice more then plugs. I think, it one is weak, it will show the least drop in rpm when unplugging each one at a time.

Another suggestion, can you use an infrared thermometer to shoot each exhaust port and see if there is a temp. difference? That may point you in the area where the miss is.

 

That's a great idea! Yes I have an IR gun.

 

Not sure how much this applies to your engine, But on my corvette, you can get somewhat of a false reading, if you dont bring idle up a little to check the temps. The cam duration can cause a misfire at idle, causing cylinders not to heat up as much.......

 

When doing a power balance test, you need to disable the IAC, otherwise, the computer will compensate for the idle drop as you disable each cylinder.

 

is that as simple as removing the connector?