Question...

I understand that the TPI system is batch fire.

Given that, will the firing always occur at #1 TDC? That is, evertyime the engine is started, it will always fire at #1 TDC?

What I'm contemplating is this...

The idle misfire is always at the #2 cylinder (though I've verified that the cylinder is very healthy mechanically and that I have adequate fuel and spark as well). In a batch fire system, with #2 being the final cylinder in the firing order, I'm wondering if somehow #2's portion of the overall fuel distribution is being robbed by other cylinders before it's intake valve opens. The runners in the MiniRam are short enough to have a clear view of the plenum and at idle speeds, the engine is running slow enough for this to possibly be occuring. If the above is indeed happening, the next thing is to figure out why...

 

There isn't any cam sync signal, so no, can fire on any cylinder.

RBob.

 

What RBob said.

In anything other then a true Independent Runner Manifold there will always be some *cross filling*. This can be evidenced by the fuel staining in the intake manifold. Enough to matter?, I dunno, the only evidence that might justify it was that a guy made 17 more HP on a 1,000 HP by optimizing the individual injector PWs.

** Not a guru, I just usually stay at a Holiday Inn when traveling**

 

Guys, thanks.

Basically, I've been fighting this problem since about Nov-Dec 2003, and it's defied all attempts at a diagnosis thus far. Even professionals can't figure it out.

This combo was running darn near perfect for six months prior. All of a sudden something just crapped out.

As far as smells go, what smells worse? Rich or lean? Does rich necessarily smell like raw fuel? Mine smells like some sort of combustion by-product, but I can't make it out. It simply gets all over my clothes and my poor wife almost pukes when she smells it. Yet it puts out no visible smoke.

When idling against the converter, creeping along at about 1-2 mph, it bucks pretty severly. Looking at either the driver or passenger side O2, I see no difference in readouts. I'm almost convinced that the root of the problem is global and the most severe symptom (a misfire) happpens to be localized at the #2 cylinder. However, off idle, the car is a rocket and smooth as silk.

 

Do you know anyone around there that's really good with a scope?. Maybe a Jr College?.

Almost sounds like maybe a poor spray pattern.

A leak-down test would tell if the chamber's being sealed, then a new plug, plug wire, cap, are about all that's left. Ignoring a vac leak, which some that go from the runner to lifter valley are hard to find.

 

Grumpy... yeah, been there done that...

Leak down test showed everything A-OK

Compression test... same thing

Already swapped injectors for another set... no change

Completely new ignition system... no change

Resealed the manifold for the third time a couple of months ago... no change

Believe me, you name it, I've tried it.


A friend from the Second Gen Camaro Owners group recommended someone to me recently. He's nearby, so I'll probably head over there when I get a free weekend. Supposedly he's really good with thirdgen stuff. I'll tell ya, if I don't lose all my hair naturally, it'll be because I've yanked it out!!

 

You didn't mention igntion scope.

 

Houston, we have misfire.

Could be a stuck EGR valve. That'll quickly cause similar problems.

Get the timing light out. Verify top dead center with a piston stop and check the balancer.

Pull the valve covers, and spin the engine by hand. Look for differences.

EGR valve gets my bet though.

edit:
DOH, miniram..... n'ermind that EGR thing. Look in the distributor.

 

Yeah, hopefully that guy I mentioned has one. Hopefully it'll tell me if it's ignition related or not.

Did those two weeks ago.

 

Pickup coil in the distrib?

They cause all kinds of fun things from unidentifiable(seemingly) steady misses to randon ignition cutoffs to that surge here or there. Early 90's trucks ate them to high heaven if u ask ang GM tech near you. Our cars (yours to a lesser extant) are abusive underhood environments due to the low hood profiles and lack of space underneath the hood for fresh/free air

Every GM car I had with a distrib had ate a pickup coil at one time or another . I've taken out ditributors and had only one pulse felt when u spin the shaft. (should feel 8 pulses for the coil/reluctor).

My last one till I swapped out a borrowed unit would actually run the car when u could feel only one pulse when it was removed. Ran like poop, but still ran.

Check the pickup coild and the wire leads to it very carefully. They should be out of limits to each other and the the ditrib casing itself(not shorted) and should generate .35-.5v AC when cranking. Also the wires inot the coil crack were they are bent up into the coil itslef(use a mirror) and the insulation also gets burned over time and comes off the actual coils. One strand is all it takes to short or miss.

I have also seen cracked reluctors in the dissies as well. Cracked and together and cracked where pieces are visbily missing.


Hope this helps u out,
Jeremy

 

Want to find out what's going on... have you gotten it to buck and just killed the ignition and checked out ALL the spark plugs? They tend to tell you exactly what's going on and they'll tell you which cylinders etc. If you notice something funny about a spark plug, clean it and swap it into another cylinder, repeat the process and check plugs. You'd be amazed how fast I figure out problems just checking plugs.

 

Hmmm... so you're saying if I bring the car up to temperature, idle up the street and pull into the driveway, that's enough time for the plugs to register the operating condition?

 

Should be enough. In just 1 second at 1200rpm each cylinder has fired 10 times. A couple seconds and it'll tell you a lot.

 

You can tell if the problem is internal or external with a scope and a sharp operator. The firing voltage, and slant of the firing line, can tell alot about what's going on.

 

Well, I tried this and as expected, the plug looked exactly like all the others. A really light tan color and clean. No residue, oil, gas, etc.

This is what has been so maddening about this whole thing. No amount of inspection or diagnosis can detect anything wrong with this car! It just freakin' misses at idle! Every electrical connection is perfect, fuel pressure is dead on, I have fuel spark and compression on every cylinder, no cylinder head problems, no vacuum leaks, no exhaust leaks, no fuel system problems whatsoever, no sensor problems, no codes, tried countless variations on spark timing values, O2 bias constants, fuel corrections, multiple different ECMs, tried a factory AUJP PROM (VATS deactivated, of course).

I guess I'll just have to see what the scope turns up.

Almost ready to post some sort of reward notice for anyone who can figure this thing out!

 

Have you tried unplugging the IAC?
Have you moved the fuel injectors around? Ohmed them? What about switching plug wires, and injector wires bank to bank.
How have you varified it's the 2 cylinder?

 

do you have a different set of injectors that you could swap in? Or perhaps move the injectors to different cylinders to see if the problem follows the #2 injector or any injector.

Probably something silly that's hiding just out of sight. Maybe try moving spark plug wires around too.

 

Well, here's everything I've done thus far (not necessarily in this order). Nothing has been able to correct the misfire/rough idle:

1.) Checked or replaced every component in the ignition system- including a brand new distributor. All spark plugs show a light tan color and are clean.

2.) Checked every component in the fuel system for leaks, cracks, pressure, dirt, filter cleanliness, etc. Verified fuel pressure. Swapped injectors around to different cylinders, swapped all injectors with a different set. Current injectors are are new within 5000 miles.

3.) Ran leak down and compression tests on all cylinders. All cylinders were fine. Cylinder heads have been pulled off and checked out by Air Flow Research. Rechecked the valve lash.

4.) Verified the emissions system is functioning properly. Consists of Charcoal cannister purge and PCV. AIR and EGR have been properly disabled within the EPROM.

5.) Scanner shows nothing out of the ordinary. Fuel correction values (long term and short term) are right on the money at 128. All sensors are new and show the correct values on the scanner for idle conditions. Ran sensors across a sensor tester. Tried sensors from other like-vehicles to try to isolate any potentially bad sensor.

6.) All new vacuum hoses. Replaced all manifold/throttle body gaskets. Engine is pulling 16" Hg in Park and at 650 rpm. Idle is steady (not "hunting").

7.) Had the car in two different shops in order to diagnose the problem. Neither one could figure it out.

8.) Rewired the entire EFI system with a new harness from Painless (even after I ran a continuity and voltage input/output check on the old SLP harness). I didn't find any problems with the old harness, but I figured what the hell? Also replaced the ECM twice. I've re-verified all the grounds, power wires, sensor wires, etc by backprobing the ECM connectors.

9.) I've also done a tremendous amount of reprogramming on the PROM (spark timing, fuel, O2 constants, air temp constants, etc.) trying to tune the problem out, but to no avail.

10.) Swapped valve lifters with a different set (thinking I had a lifter(s) go bad)

11.) Took out the original ZZ4 cam to inspect it. It was fine. But while I had it out, I put in the current Comp Cams one that I have now.

12.) Had the alternator checked out to verify no AC current leakage. Also ran the car without the alternator to re-verify (making sure the ignition system was still receiving a full 12V).

 

When you find the problem let me know. My car has done the same thing since the rebuild. (I'm betting on the sticking EGR or weak pickup coil on mine.....)

 

Well, new doesn't always mean works right.

How BAD is the misfire. Is it a bump every second? Just runs really rough at idle? Every few seconds per miss?

I've seen fuel pressure regulator diaphragms tear causing general problems. Is it referenced near that cylinder?

 

How do you know it cylinder #2 that's misfiring?

 

I've verified each item with another one to be certain.

Most times it's a very definite harmonic with a discernable frequency. Other times it just feels rough- even like a multiple cylinder misfire. However, after about 1200-1500 rpm, it all disappears or at least becomes undetectable. The power output at that point is fantastic as well as smooth.


As a matter of fact, it is. It's referenced on the passenger side, forward vacuum port. But the closest cylinder is #4 which has no problems. But wouldn't a torn diaphragm cause pressure problems? I have correct fuel pressure at full vacuum and low vacuum.

 

When I go around the engine and remove one spark plug/fuel injector plug at a time, the #2 cylinder has little or no reaction as compared to the others. The scanner registers no response. I have an O2 sensor on the passenger side as well as the driver side, so I'm able to look at both sides of the engine.

 

And you're showing the right side is running richer than the left on the O2 sensor? If so, have you traded the 2 O2 sensors' sides?

Have you checked the distributir for run out and possible worn gear? How about the cam sprocket for the distributor gear? Look okay?

 

Actually, both sides run the same! You'd think the passenger side would display differently, but it doesn't. And I've swapped sensors too. Believe me, two and half years is a lot of time to do diagnosis. Unless there's some really screwy thing that nobody is thinking of, I've done everything... (yes, except for the scope, Grumpy! )

 

BTW, I really do appreciate everyone's input and willingness to stick with this.

 

What is the timing doing when you're idling?
Have you swapped the injector connector sides bank for bank?
Get yourself a yellow crayon and mark each header tube, watch them closely and see if the #2 cylinder takes longer to burn the yellow to brown.
Have you tried unhooking the tan wire (ESC bypass) to disable the ecm's spark advance? If so, what does it do?

 

If you have a temperature gun, you can check the exhaust temp for each cylinder. If one is misfiring it should have a lower temperature.... That could indicate fuel fouled plugs.... They would probably dry out while the engine is cooling down (depending on how bad they are fouled) and cause you to miss them.

I hate to ask this, did you check the heads for cracks???? Also, what O2 sensor are you using? A three wire sensor would react faster than a single wire unit (or so I'm told, hope to find out in another week when I have the time to install mine) and it might make a difference.

Another thing to look for, and I thing it was mentioned above, check for a spun outer ring on your harmonic balancer. That's normally the mystery miss on a TPI...... everything has to be in perfect balance with a TPI otherwise the distributor pulses get off slightly and throws things for a loop... That's why I normally run a Fluidamper and a Mellings 7 vane oil pump.....

 

Holds steady. I disabled the spark advance/retard rpm correction.

Yup.

I used the "squirt water on the tube" approach. At operating temperature, I squirt a little water on each tube. On tubes 1, 3-8, the water boils off instantaneously. On #2, it takes significantly longer. Cold tube equals a rich running cylinder does it not?

Yeah. Not much change. But it runs a little rougher.

 

Like I said in the previous post, I used the poor man's temp gun- a squirt bottle with water in it!


Air Flow Research examined heads for me last year. Didn't find anything wrong with them.

I'm using a Delco AFS-74 heated O2.


Are you saying that the outer ring of the damper can move relative the crankshaft position? How would I even inspect that? What would it look like?

 

If you have a standard factory harmonic dampener the outer ring can move. It doesn't have to move much to cause an imbalance. This imbalance will cause a miss that you can't fix by changing plugs, wires, dist. cap, etc....

I have spun the outer ring on my first 1985 Z28 with the TPI 305. The car I have now had a new TPI 305 in it due to the outer ring slipping. The imbalance caused the main bearings on the previous owner's engine to go out.

The balancer on that new engine went out 10K miles after I got the car. I installed a 6.25" Fluidamper and it ran fine for the next 50K. Installed that same balancer on the first 350 in the car (with lightweight pistons) and ran it another 50K. I changed it for a 7.25" unit on the current engine since I couldn't seem to find the miss and was afraid the smaller balancer wasn't enough to handle the heavy pistons currently in the engine. That in itself gave it a surging idle until the car warms up. Could be due to the larger amount of fluid in the bigger dampener needing to warm up as well.

How to check for a spun blancer: Look to see if the rubber between the inner and outer rings is cracked, torn or bulging. That would be an indication. Other than that, swapping for a buddy's that you know is good is the cheap way.... Again, just a thought..... BTW, I borrowed the temperature gun from work over a weekend.... :-)

 

That cylinder is getting intermitent spark. If it was fuel, even if it were rich or lean the exhaust would still be very hot. From hear on out work on the spark. When you say you've disabled it you mean you've unplugged the tan bypass wire and set the base timing to 6 degrees at idle?
As far as the balancer thing is concerned just pull the number 1 spark plug out and get yourself some coat hanger. Rotate the crank over using a large strong screw driver on the flexplate and trans housing. Find the top and the "TDC" should align with the pointer. If not your balancer is off and so all your timing is off. Are you running a virgin GM bin until you figure this out? The timing on the GM bin's is very conservative and will help you figure out the problem. Might try a hotter spark plug and see if that helps, although at idle it shouldn't but it might be fouling.

 

I was thinking about the balancer thing, but I may have disproved that when I verified top dead center a couple of weeks ago.

Used a piston stop to locate #1 top dead center on the damper vs the timing mark on the timing chain cover. It was dead on.

In addition, the balancer looks to be in good order when I inspected it last night.


On the bypass wire, I currently have the base timing set at 10° BTDC to match what I have as the base timing in the constants table in the EPROM cal.

However as a test, last year I put in a factory AUJP cal and set the timing to 6° with the connector unplugged (in order to see what would happen with a factory cal). It didn't make any difference.

I just know that when I find out what's causing this, it's going to be something so stupidly simple, I'm going to have to leave the hot rodding world out of shear embarassment!

 

Something that may or may not be relevant but thought after all you'd been through I spit it out
When I installed my Sportsman II's I drilled the EGR passage per the specs.
The place where it comes from is one exhaust port on each side.
Maybe there is some reverse flow going on at certain times or something causing that cylinder to go lean.
I don't remember which cylinder the port is drilled into but disturbed me a little that one port was used and that backflow in the exhaust from other cylinder discharge would be required to get functional flow to the EGR all the time.
I don't know if there is something there to look into with your problem.

 

Only thing is, the AFR's don't have any EGR. Neither does the MiniRam.

But thanks for the input. At this point everything has to be laid out on the table.

 

I think I got it. It's got to be those stuborn unobtanium piston return springs! You know, the one's that push your piston back down so they can come back up .
Really though, I think you're best bet might be to install an EGT and get a friend with an o-scope to poke and prod because no multimeter is going to figure this one out.

 

You'd think a bad cam lobe would show up on a compression test....

 

A bad lobe is easily found by pulling the dip stick and checking for metal glitter.

 

Just discovered another piece of data today.

When I pull the PCV valve out of the rocker cover (vacuum hose still attached) and I put my finger over the valve, there's no change in the engine RPM. There's definitely a suction pressure, but no change in RPM. I would think that if the engine is drawing air through the valve, blocking it off would cause the rpm to go down?? It's a TPI L98 PCV valve.

I disconnected the IAC motor to verify no RPM change it (since I have the idle speed set such that I have zero IAC steps in Park at 650 RPM). I wanted to make sure the computer wasn't altering the IAC inlet to compensate.

Don't know if this means anything...

 

A guy at work described the same type of problem with his GTA. Found the throttle shaft in the TB to be excessively worn causing a vacuum leak, replaced the throttle body and problem is gone.

BTW ULTM8Z love the 2nd gen real nice ride.

 

As far as vac leaks there is a trick I use in hard to find cases. Please be carefull , spray a small amont of brake clean and watch O2 Mvs if they change you found it .

Also does mis happen at cold ect or does it come on and get worse after engine is up to temp?

 

Ya know, that cam lobe idea maybe something to consider. IMO, using an oil analysis co., might be worth the $$.

On pinching off the PCV, it sounds like your idea, maybe rich.

 

Guys, I can't tell you how much I appreciate your thinking about this issue.


Cam lobe: I had the same problem before I changed out the ZZ4 cam for the Comp Cams one. The ZZ4 cam showed no signs of excessive wear. I even measured it to be sure.

Throtle body leak?: I thought about this one to. However, on a MAP car like mine (barring a leak directly into a cylinder) wouldn't any vacuum leak become part of the overall airflow into the engine at idle? I've adjusted the throttle blades to give me zero IAC steps in park at 650 rpm. That adjustment would have taken into account any other air leaks around the throttle body, wouldn't it? On a MAF car a leak occuring after the MAF sensor would be air that the engine didn't measure and would be a problem.

I'd really hate to spend a lot of money on a new throttle body only to find out that it's not the problem. Is there a test I can perform on the one I have?

I've already resealed the manifold gaskets three times and have checked for leaks above the ports by putting a little bit of water there. Nothing was sucked in.

Rich/Lean?: The other day, I went into the constants table and adjusted the rich/lean threshold at idle down to .250. Can't say it runs any better, but the BLMs went from 128-132 down to 118-120. And again, both sides have BLMs that are within 2-3 points of eachother. Does that tell me it was running rich?

 

Have you tried forcing an open loop? If the problem isn't there then check the spark plugs again to see if you do have an intake leak on the #2 cylinder, it'll show up leaner than the rest.
In anycase I think a wideband o2 might be in you're near future. You'll be able to see exactly what the AFRs are doing.

 

I did that a little while ago. But I forgot what the results were. Maybe I should go back and try it again. I don't recall any light bulbs going off in my head when I did try it though...

 

ULTM8Z - did you know your website was down?

 

I've seen some odd behaviour from worn throttle shafts. I haven't dealt with any EFI throttle shaft probs, but on carbs, they can be a royal PITB to find.

 

From the handful of loose throttle bodies I've tinkered with the only effect was an increased idle. My worn shaft on the Holley TBI was a real pain. It wore evenly (a return spring on either end unlike OEM) but because it wore to one side and down the throttle blades started catching and not closing! In other words the worn shaft wasn't hard to find, it pretty much told me with the high engine speed .
With a carb I bet that would be really annoying.

 

Yeah. I already contacted my ISP about it. Hopefully it'll be back up soon.

 

Guys, is 3 ms too high for injector pulse width at idle speeds?