4.3 vortec misses on 3 cyl

I have a 94 s10 4.3 vortec which is missing on #s 2 4 6. Compression is good. spark is good. injector is new,fuel pressure is good. plugs are new. converter is gone. What would cause a miss on those 3 cylinders? It happened all of a sudden. Engine has about 70, 000 miles. It appears to be flooding the plugs on that bank. O2 sensor reads rich all the time.

Try replacing the wires, router, and the distributer cap.

Cap and rotor are new and wires scope out fine. Thanks

Check your distributor shaft for play. Have seen more than one with bad bearings. What happens is that the reluctor hits the pickups and will cause a no fire.

I think the injector is faulty.

When a bad injector is seen, it will flood a bank like that.

I have been there this baffeld me for a whiel You may have already replaced the injector spider and seen fuel on one side of the manifold
the issues it the lines in the back of the manifold that feed the fule are very high pressure and the tiny hairline cracks in then after they get old dump fule into the manifold whiel running .. so if they have never been replaced then you will need to do that. it is all one kit that includes the piece that the lines are attached to. you take them off from the back of the manifold and slide the new ones in. Good luck tis fun.

This can be diagnosed by seeing washing in the passenger side of the plenum.

If it is on the passenger side, it is the CPI injector again.

I will see in the morning. I have another new injector and ordered a Nut kit also. I cant see how the nut kit can cause a leak on the passenger side but the lines have 176K miles on them and has a small rub mark where the injector line were rubbing. Is it possable that the vacuum is pulling fuel past the pressure regulator orings even though it is new 0 miles? I pressureise it with the upper plenum off and it does NOT leak. Gary

Well, Another new injector and a new nut kit and same thing still. Not running on the right bank and the plugs are flooding out still. Tested the wires with a ohm meter also and still ok. Seams to run ok at high rpms just not below 2000 or so. Distributer shaft seams to be tight. What else could cause a miss on 3 cylinders?

Ok, let's go through your list:

Compression is good
On your second CPI unit
Plug wires ohmmed out good
Fuel pressure is good
New plugs

1. Have you checked your cap for any cracks?
2. Have you inspected the reluctor in the cap for cracks?
3. Do you have a brownish color dust on the inside of your cap?
4. Since it is the entire passenger side that is not firing, have you checked to see if all 3 wires are not pinched or twisted together?
5. Was any work done on the engine prior to this happening?

Yea, seems like maybe a bad cap and rotor problem.

Cap and rotor are new. They were really bad but no change. Wires are correct and have the correct resistence. There is plenty of spark to the plugs. When sprayed down with water they do not arc. Changed the plugs twice. Distributer shaft is tight. Going to try a different distributer tommorrow but dont put any faith in to it. I actually ran better with the big hose to the brake booster off (got in hurry and forgot to hook it up by accident) so it is diffently getting too much gas. Scanner shows rich condition all the time. Egr is closed. ECT is reading correctly. Going to try a different ecm tommorrow even though it doesnt make any sence. As far as I can tell this injector fires 6 times for every revolution and is common to both sides. Worked on a freind tow truck 2 weeks ago and it was missing on one bank and it was beacuse the ecm was loosing ground to one side under load.

Hold on a minute. You sound like you have a little knowledge here. What you are saying can be true but the CPI has only two wires to it. If the one bank works the other will also.

As far as the distributor goes, when you changed the cap, was there any brownish rust in it?

I just reread your original post. Did you just install the CPI unit?

Cap and rotor are new. They were really bad but no change. Wires are correct and have the correct resistence. There is plenty of spark to the plugs. When sprayed down with water they do not arc. Changed the plugs twice. Distributer shaft is tight. Going to try a different distributer tommorrow but dont put any faith in to it. I actually ran better with the big hose to the brake booster off (got in hurry and forgot to hook it up by accident) so it is diffently getting too much gas. Scanner shows rich condition all the time. Egr is closed. ECT is reading correctly. Going to try a different ecm tommorrow even though it doesnt make any sence. As far as I can tell this injector fires 6 times for every revolution and is common to both sides. Worked on a freind tow truck 2 weeks ago and it was missing on one bank and it was beacuse the ecm was loosing ground to one side under load.
Well I though I had a lot of knowlage untill working on this truck now I am wondering. Cpi is new on Monday and again to day. I dont think there was any rust but the carbon from the center electrode of the cap was gone. Could not see the gas stain on the fuel regulator like I saw a year ago when I dd one of these on a 95 Blazer. Fuel pump holds pressure very well and trucks starts perfect. Nothing else was dont to this truck. It was running fine till 48 miles ago and it happened all of a sudden. ?

Check your EGR valve.

You have done a lot here in a short time and please don't take what I say here the wrong way. Do you think that you may have solved your problem but introduced another?

For example, are you sure you put the proper injector in the proper port?

Sure you didn't cross any wires on the one side?

I'm sitting here running this over in my feeble mind and trying to see what is common to the right bank only.

Yes, I want you to know I am happy for any help you may offer. I have checked the firing order. 1 6 5 4 3 2 in clockwise direction. First thing I did was check the fuel pressure because I have seen bad nutkits before and pressure would leak down and it would be wet on driverside not passenger side. Blown regulator will cause leak on pass side. I installed a genuine Delco$$$$$$ CPI unit and I installed lines the way the old ones were.I dont think it matters although because it fires all poppets at the same time on this year. Newer ones are different.......slowly going bald one handful at a time. Called a neighbor of mine who has been a GM tech for 30 years and he didnt have any answers either?

BTW I tryed to pull EGR al the way off and one bolt on the passenger side is very tight and could not get but 3 turns out of it. But i could pull out the other bolt and was able to get my finger in it and egr is clean. I have changed many of these and it is not the problem. My scanner shows the egr to be in the closed position. Thanks

Here is an idea,,, You appear to have a good background so I will make it short and sweet.

Do you think that perhaps the lower intake gasket on the one side let loose?

Funny you say that. I am going to try to run propane into the valve cover to see if it runs different. I already checked for external leaks. My only problem with that is it should be lean and not rich.

Says HELP? Anyone? Any one?

Says HELP? Anyone? Any one?

Waiting to hear back on what happened with the propane.

Propane enrichment ....No help. Vacuum leak was a good Idea but not on this one. Has any one seen a bad run of CPI units. These were both Delco units. I couldnt find a test disributer. So I havent subed that yet but I have good spark and the injector is pulsing or it wouldnt be flooded. i a going to change the wires just because biu it is just throwing money at it. Gary

Well, I popped the exhuast pipe loose on passenger side and it seams like it is clearing up. Plugs are fouled but with soot not gas dripping off them. I was told these have double wall pipe and one may have colasped. Any body hear of that? The converter has been cut off and a small pipe was welded in its place. That is why I didnt drop pipe 2 weeks ago. I will let ya know tommorrow.

Did you check the nut kit yet?

Well, I popped the exhuast pipe loose on passenger side and it seams like it is clearing up. Plugs are fouled but with soot not gas dripping off them. I was told these have double wall pipe and one may have colasped. Any body hear of that? The converter has been cut off and a small pipe was welded in its place. That is why I didnt drop pipe 2 weeks ago. I will let ya know tommorrow.

Son of bee with an itch. I have seen that before but did not think of it cause I didn't know these were doubled wall. It sounds very plausible.

Well......NO, It just sounded better. Still flooding. Got it hot and pulled upper intake off again, 7th time and it is still soaked. Have third CPI unit coming now. I got a different brand this time. And yes the Nut kit is new with the second cpi unit.

Did you use the o-rings around where the nutkit attaches to the injector?

Yes it has new Orings and yet a third CPI unit. This one from another vender. No change. I give UP.

I still think it has something to do with the cap and rotor.

If the rotor or cap was out of alignment somehow, it would explain why the one bank is not burning properly if the spark is having to jump an increased distance in the cap.

The cap and rotor are lined up fine. I have had them off several times. It is missing every other wire in the firing order not one side of the cap, one side of the engine.

We had the plenum off today and caught it spraying fuel out of the regulator area when cranking. It only did it once and was not able to check the fuel pressure so I dont know what is was reading. Too much pump pressure? Fuel pressure gage is viberating when engine is idleing but not under accel or decell.

We had the plenum off today and caught it spraying fuel out of the regulator area when cranking. It only did it once and was not able to check the fuel pressure so I dont know what is was reading. Too much pump pressure? Fuel pressure gage is viberating when engine is idleing but not under accel or decell.

Isn't that your third CPI unit? Well, if it is doing that, that would explain that bank being flooded.

I have never noticed the guage vibrating while at idle on a CPI unit. I believe it would be possible if the regulator was screwing up. I know you have dumped a lot into this but perhaps, since you saw it with your own eyes, you might want to change the regulator only.

Thanks every one for your help. I found an old post and emailed the poster. He had a similar problem with a broken valve spring. Replaced the valve spring on cylinder #6 and it runs like a top.

?

You said the regulator was spraying fuel.

That is the problem, replace it. It is supposed to be dry at all times.

Thanks every one for your help. I found an old post and emailed the poster. He had a similar problem with a broken valve spring. Replaced the valve spring on cylinder #6 and it runs like a top.

I assume that this was an intake spring?

Yes it was, and it passed the cranking compression test 3 times before it failed. It did not fail till we tryed a different compression tester.?

Again, you said the regulator was spraying fuel again.

Did you replace the whole injector or just the regulator on the side.

Apparently the fuel was building up in cylinder number 6 and after enough of it built up it would blow out of the cylinder and soak the injector. We did not replace any thing in the fuel system this time only the valve springs. Yes this was a very strange problem but I guess I am not the first. It would never spray out when we were directly looking at it only when we turned our head for a second and that is why we could see the fuel on the injector but not where it came from. The spring that broke was broken under the little cover on top so you could not see it with out removing the sping from the engine. I wont soon forget this problem.