Pass side miss,huff,chug

[wcamaddox]

DELPHI Part # CZ20003 is the one I bought. And I would love to report that after putting it in it cured all my woes but alas I cannot. It gets warmed up misses in cylinder #4 P0304 code. stftrm -50% ltftrm -15%. I am completely out of ideas...... I can tell you what its not. opti, plugs,wires,O2 sensor, TPS, compression, fuel pressure, injectors, vacuum leak.

Now my question is this. The passage for the IAC in the intake itself. Does that passage run to each individual cylinder? If they do could it be possible that just the #4 passage is clogged, making it run rich, causing my misfire and the O2 sensor to read over rich and thats how I get my fuel trim in the negatives?

I know a long shot but I am running out of things to check/change lol

 

[paart]

The IAC is simply a PWM controlled "pintle" valve that directly connects to the ECM to control the idle speed by controlling the airflow. It's attached to the side of the throttle body and ports directly into the intake plenum. I don't believe that it could affect just one cylinder.

As I understand things, the engine runs correctly (number 4 fires normally) when dead cold, but misses on #4 when warmed up.

When the engine is cold, the mixture is controlled by the ECM, and will typically start out rich, leaning out some as the signal from the temperature sensor increases. At a certain point when the temperature sensor indicates about 180 degrees, the system switches to "closed loop" mode and relies on the O2, MAF, and MAP sensors (and others) to calculate the fuel trim. I have to admit that it is odd that only one cylinder would fail to fire only in open loop mode. I'm guessing that the rich condition reported by the O2 sensor is simply the unburned fuel from #4.

I think you mentioned that you have a "spark plug tester". I'm not sure you'll see anything, but I'd try and look at the quality (blue-strong) of the spark under both "cold" and "closed loop" conditions.

I'd pull the electrical connectors off both the #4 injector and the ECM and look for any sort of corrosion or similar problem.

Do you have access to an oscilloscope?
Did you say that you replaced all the injectors?

 

[wcamaddox]

Yep, replaced them with a set that was cleaned, back flushed, flow matched, new basket filters etc. I had two I know were bad. I have an older oscilloscope. Well my dad has it so in turn I can use it lol. I did today start looking at basics again. pulled valve cover watched the rockers work.... just so I was absolutely positive they were. Still have like 154psi compression. Cleaned the plug up. I checked the #4 injector wiring for breaks. Tested the resistance of the sensors I could. TPS, IAC, MAP, I am getting 11.4 or so volts at the injector plug at key on. I will check the ECM wiring and plugs here in a bit, I have a leg problem so I do things in spurts......
I still have a reading from my O2 of .720 - .730. Thats the farthest it fluctuates..... In closed loop. Open it moves from lean to rich like what I would consider a normally functioning one should...... I dunno. I am fairly certain its probably something stupid that I would bash my head against a wall after I figure it out..... I know a leaky exhaust manifold gasket would cause the O2 to think its lean, the opposite couldnt be true could it?

 

[paart]

I'd try to look at the pulse width signal on the #4 injector, during cold and warmed up conditions, and compare that to say, #3 or #5. I'm wondering if #4 isn't lean, and when it goes closed loop, it leans to the point of misfiring. If you are certain the cylinder doesn't miss when cold, I'd figure a way to keep it in open loop. Disconnecting both O2 sensors ought to do it, perhaps putting the old ones back in (unconnected), if you plan on running it long.

The O2 sensor on my '01 Chrysler minivan is dead, despite several attempts to repair the issue. It runs as good as ever and gets better fuel mileage than with the O2 sensor functional.
..........but that's a story for another time. 🙂

 

[buickwagon]

The scope is best, but failing that a noid light will at least tell you if the injector is getting any voltage at all. With either the scope or a noid light, compare to an adjacent cylinder.

 

[wcamaddox]

Well if anyone is interested the LT1 intake does indeed have a separate set of air passages that the IAC air runs through to each individual cylinder. Take off the heat shield on the underside of the intake. There are 5 large pipe plugs. Remove those and viola, IAC passage. Mine were definitely nasty. Dunno if it will help my issue but I know cleaning it up will not hurt it any. I am also thinking about changing all the plugs. Maybe after it sitting a while when it first started it done something to them. I don't know for certain but there cheap. Waiting on leads for the oscilloscope, the price was right for it so I wont complain about buying leads......
Still haven't a clue whats going on so grasping at straws I guess. Weird thing is it only does it at idle, above idle its like I burned off/pushed the extra fuel out the tailpipe and it runs better than it ever has. Scary at first that a car this size gets up and goes that well.
Oh well, waiting on a new PCV grommet, than I can hopefully get the intake back on and see where I stand.
Regards,
Bill

 

[paart]

Whoa! Now that's interesting! When I had my intake off, I had it "tanked" (cleaned) at a local shop. They removed the plugs, but had them reinstalled when I picked it up, so I never saw the inside of the manifold. The passages that you found are undocumented in the FSM. If your "miss" is only at idle, I'd think that you may have a reasonable chance that you've found the problem.
A tip--Use a GM PCV grommet. I purchased one at Advance Auto, struggled close to a hour trying to get it in place, and then purchased one from a local dealership (at a lower price than the aftermarket). The design of the GM one was different, and was easily installed in the manifold.

 

[200OZ]

I thought the passages were for the egr, no?

 

[wcamaddox]

Nope, not the set I found unless they do double duty. The IAC air goes in the little hole in the front of the intake, down to the underside of the main passage and each individual runner has an air outlet from this passage. Confirmed when I was rinsing out the cleaner I was using and the air hose to dry everything out. Trying to get it all together today, wanted to past couple days but I forgot the wife was hosting some kind of party so I got worked like a borrowed mule to prepare for it oh well, I will tinker today... than go to work tired but hopefully in my Roadmaster.....

 

[wcamaddox]

Well I did get the intake on today, all buttoned up and started.... well I still got the p0304 misfire... that is until I was searching for possible vacuum leaks..... one of those things I do after I swap a manifold, just in case. Well I sprayed m\by my PCV valve and my idle changed. So I removed the hose leading to it. Well the idle changed(of course) but it sounded better. So I let it idle a bit like that. Well my misfire went away. No joking So I reset the codes.... It was idling 900-950 or so, sounded good! So took it for a cruise around the country mile. Started running even better. Code never returned. Even after letting it set and idle in the driveway a bit. Sooooo my question now is anyone know what these are supposed to idle at? I know the IAC is supposed to control it but there should be a base idle. My anti-tampering cover on my idle screw is missing so maybe someone fiddled with it before and now its wrong.... 600 rpm sounds a little low to me. 900 rpm and my issues go away. so I guess tonight at work I search for a idle set procedure. Or do I just have a effed up PCV valve thats not letting enough venting air go by it?? I will go get another one there way cheap and all.
So the next adventure begins.... Thanks everyone for their input so far, you really have made me better at remembering the dang basics and what to look out for. Oh well, tomorrow is another day LOL
Bill

 

[paart]

The FSM states that the IAC will control the idle "down to" 700 RPM, but if the idle is above 800 RPM, then check for a vacuum leak. So--700 to 800 seems to be the range. The obvious question is--have you checked the hose to the PCV valve?

 

[wcamaddox]

Yeppers, I didnt have it all the way on so thats why when I sprayed it, it idled up. It had from what I could see quite a few vacuum leaks when I got it but it ran well so I didnt really look for them at that time. That and a intake gasket leak I found when the engine was out. It idles so low that turning the steering wheel makes it want to die. So I am wondering if it had leaks and as a "band aid" the previous owner idled it down at the screw, but now that I have all those leaks fixed it idles way too low? I dont know for certain. All I do know is is that with the PCV hose deliberately off the valve it idles normally(albeit a touch hi) and I do not get the P0304 misfire. The data from my scantool shows everything fluctuating like it should adjusting for what the sensors are reading. Plug it in, it idles down to below the 700-800 target you told me about and it misses out. So. It must not be getting enough air, loading up with fuel, and makes the O2 read rich and ECM pulls fuel and whamo misfire. At this point this is a "best guess" with what I know right now. I am waiting on test leads for my oscilloscope to check the injector pulses.... But like I said, it was free so I wont complain......

 

[buickwagon]

What does your scan tool say is the desired idle speed? What does it say is the idle air position %?

The system reads the value of the throttle position sensor at start up and establishes that as 0 degrees throttle for the rest of the run cycle. The PCM will try to hold the isle speed to the desired idle speed using the idle air control.

If you twiddle the stop screw to open the butterfly, the TPS value increases and the PCM sees that as giving the engine some throttle so it does not attempt to bring the idle back down with the idle air control.

Until the next time the key is cycled, establishing a new baseline value for 0 throttle. The PCM will then try to set the idle to the desired speed using the idle air control. You can keep playing this game until you reach the maximum travel of the IAC, at which point the PCM will throw an IAC code. Or possibly a TPS code if that is now out of the acceptable range for a 0 value.

If you really need to raise the idle, the best way is to reprogram the PCM and give it a new desired idle speed. Which of course is different under different circumstances, such as when the HVAC system has turned on the AC compressor.

 

[wcamaddox]

I dont have that fancy of a scantool, I wish I did but being just a home mechanic I buy the best I can reasonably afford......I am however trying to find a copy of freescan and a usb to obd2 connector. And I did replace the PCV valve with the correct one, the one I put in was for my Regal... I put them in my cart (an old medcart) I use for tune-up and oil change stuff and grabbed the wrong one.....

I didnt twiddle with the idle screw, figured that it has to be something else just think its weird that when it gets extra un-metered air that all my problems go away, like it really is starving for air which is causing my rich problem and fouling out the plug in my #4 cylinder causing my misfire. I did however adjust my tps to .69 volts (its as close to .67 as I could get)

So I am down to bad IAC Either that or my ECM is giving me fits.... there isnt a lot of info on diagnosing the fact my computer may be bad. I mean it does let me read info but how do I know its accurate? or maybe the drivers for the bank 2 of the car are acting up and cauusing all my issues. At this point I wont rule it out......

 

[buickwagon]

Did you ever have the opportunity to check the signal at the injectors? Either the waveform with a scope or the approximate duration with a scope? I know you changed the injectors themselves, but maybe #4 is getting constant power instead of a timed pulse?

 

[wcamaddox]

That is my next step. I am awaiting the arrival of my scopes test leads... they should be here anytime. I cannot complain to much though because I got it for free. Also from looking at things on it I can hook up 2 sets of leads and directly compare two test subjects to compare the directly on the scope. That will be handy testing one injector to the others I believe!

Regards,
Bill

 

[paart]

I sounds as if you've acquired a dual channel "bench" scope for good price (free)!
If so, and it is not a unit specially designed for automotive ignition testing, do not attach a lead to the spark plug wires and attempt to look at the ignition output directly. Even with a 10X probe, 2000-3000 Volts can be applied to the scope input, which will "fry" it, in most cases.
Special inductive probes that surround the plug wire are used for this purpose.

 

[buickwagon]

Not to mention that the 600v CATIII probe insulation isn't up to the task of handling ignition voltages...😱

Actually, you can probably get away with a couple of regular test leads and a BNC to banana splitter from Radio Shack for now, as long as the scope input can handle 20v or more (300v is pretty common). The signal will be a bit noisy but the injector pulse should be well above the noise. Just remember to set the input for 1x, not 10x.

 

[wcamaddox]

Well sorry its been so long since I have last posted but it seemed like the leads I ordered were on a slow boat from china..... I did get it hooked up to the car.... I made some test leads from and old pair of injector plugs so I didn't have to poke and prod my cars wiring.... well it looks like the waveform of the #4 injector is the same as the other 7. Because it is a dual channel we could impose the signals on top of each other as near as identical as I could tell at least...and it did not appear to change whether it was in open or closed loop. So for giggles the local parts store let me use a IAC... no change.... totally unplugged the injector..... O2 readings do what I would call "stabilize" I guess, they seemed to mimic the other bank... O2 reading moved up and down instead of pegged at a constant .730 so I am at a total loss here... thinking about breaking down and having the local "stealership" look at it..... and I now honestly believe it is my engine control module.... I do know its a 96 and hasn't shown a code for removing the air pump so it either had that update done and it wasnt taken of or ecm its fouled up? i dunno anyone think it may be something else? If not let me know! Or let me know if I can check something else... I will probably order a ECM from rockauto here on Monday..... and make an appointment to get it flashed and put it.....

Thanks for the help everyone it is truly appreciated,
Bill

 

[paart]

I don't think I'd go to a dealership at this point. You have a pretty unusual problem, here. At best, if there's someone who is really "sharp", on these cars ( You have to remember, these guys don't work on a lot of RMs anymore), they might find the issue. At worst they might start just replacing parts, including what you have done, hoping to find the "fix".

Two questions: 1/ since you are using "homemade" probes, are they wired to "pass through" the signal, so that the injector operates, while you are viewing the pulse? With both 'scope channels hooked-up to injectors, that is #4 and say, #3, do the pulses duplicate each other, from "dead cold" to fully warmed up, and idle to 2500 or 3000 RPM?

Question #3: Have you done a simple resistance measurement (ohms) on the injector(s)?