Ideas for a "miss"?

[sirhk100]

Hey everyone... Mine is your normal '91 model. I need to have my ride smogged by sat so kind of up against a wall here and running out of ideas. The engine was rebuilt 600 miles ago. New rings, honed cylinders, new heads, gaskets, seals, ground the valves, etc... Sat I replaced all the plugs and wires. The plugs I pulled out all looked text book perfect even with the miss. Coil pack is working cause I would think if it had a bad bank it would be REALLY missing considering it functions in pairs basically. Loose one, you're loosing 2 cylinders really... The miss is pretty minor. I replaced the fuel pressure regulator last night cause I found gas in the vacuum line. Replaced the intake air temp sensor tonight cause I found it was bad also. I swapped out MAF's last night, no difference. I have a spare throttle body but didn't swap cause I don't see how that would make a difference. Unplugged the throttle body though and it definitely runs different so I'm assuming it's functioning. Same with the IAC, unplug it, engine runs a bit goofy so assuming it's good. Sprayed every remote spot of a vacuum leak and didn't notice any change in engine rpm. I'm pretty confident I don't have any vacuum leaks as I just routed and hooked it all back up myself 5 weeks ago when I slapped the motor back in. BTW, I had the miss before the motor rebuild, thought it was due to a goofy cylinder I had but rebuild and still the same.

Kind of at a loss for ideas right now though. I'm going to hook it up to a smog machine tomorrow and just have it checked and try a couple things to maybe sneak it into the passing numbers and if I can get it there, we'll run the test. That will at least buy me some time but I still need to fix it.

I do have a minor exhaust leak at the passenger side collector I need to pull it loose and just remate it and tighten it back up but I don't see that causing it to run like it has a miss. I also would've thought I'd have seen something on the plugs I swapped out Sat but like I said, they were a perfect tanish brown color. I've triple checked the plug wires, they're all seated properly.

Ideas of other things to check? I don't see how the IAC would cause a miss, I could see a surging idle or odd idle RPM but not a miss. True? Throttle body shouldn't affect a miss?

How's it even really a "miss" if the plugs look great? It sounds like it's running on about 5.5 cylinders. Has power at rpm but idles rough. At the exhaust you can hear/feel it puffing like a miss. No pops, sputters, backfires, etc... Just a very mild rough idle like it's still firing on all 6 but just running a little off. I really was hoping and thinking it was going to be the FPR last night pulling extra gas thru the vacuum line but like I said, new one installed and no change other then it doesn't crank as long before it fires up now. I may pull the new plugs again tomorrow night just to check them again though. BTW, motorcraft platinums with bosh 8mm wires.

Ugh, stupid exploder!!! I can afford a WAY nicer ride then this with a cash purchase but I honestly really like my ride. Sometimes though I really wonder if the headaches are worth it though!

Thanks,
Khris

 

[vq5speed]

How does it drive does it accelerate smoothly
What RPM does it idle at..

 

[sirhk100]

Idles at high 600 to low 700. On acceleration you can feel it slightly. Nothing though like a true running on 5 cyl engine though. Funny thing is you can almost feel the rough vibration and hear it in the exhaust more then you notice it power wise. Cruising RPM of say 2200-2500 it's not even noticable in anyway. I don't remember the smog numbers but at RPM I'm right on the edge of passing, at idle though I'm way out of the limits. I'm sure it's just this stumble slight miss though that's failing me.

I'm going to hook it up to the machine again tonight and play with it a bit but actually on my lunch break in the parking lot I'm going to loosen up that collector and reseat it so hopefully I can get rid of the exhaust leak and we can hear the engine more itself without the stupid puff of a leak on the pass side.

 

[vq5speed]

So you already took it in for smog test and failed. I just had my X smogged last month and it passed. But I put a can of "CRC Guaranteed to Pass" into my tank. I've always done this and its always passed. Would if have passed anyways maybe..

 

[sirhk100]

Well, I took it for test this past Sat and it was going to fail. The smog test machine itself ended up having issues two times in row and it wasn't actually able to complete the test but it had already gone into the 2nd chance mode meaning it failed the first time for sure. I ended up leaving without paying and it didn't get recorded as an official fail because it never actually finished the entire test. So then Monday I swung by my local Jeep dealer of all places cause my uncle is a tech there and we stuck it on their smog machine just checking the numbers, not actually running the test and on their machine the numbers it was putting out definitely would've failed it.

That's what I'm going to do again this afternoon, slap it back on their machine to get the live reading of what it's doing and start checking a few things on it. We're hoping maybe we can kind of fake it thru a test to at least get me passed so I can renew my registration and buy myself some time. I still obviously need to fix it and will continue figuring out what's going on with it but at least then I don't have the stress of being up against a deadline of this Sat to get it fixed and registered as I have other vehicles to drive if really needed.

 

[sirhk100]

Well, I'm 37 years old and for the first time in my entire life I accepted defeat and dropped it off at the ford dealer for diagnostic... Will depend what they find on if I'm letting them fix it or not but I'm out of ideas. Only times any vehicle I've ever owned has ever been in a shop was for tire service and smog checks. Rebuild engines, transmissions, heavily modify vehicles, diagnose them, fix them, etc... All myself in my garage. This is a pretty odd feeling honestly!

 

[FR-425]

Which numbers were off?

Oxides of nitrogen?

Hydrocarbons?

If it's high on the Hydro's I would suspect the ICM. (delivering full pulse width at all times(RICH) Note: this condition will not produce a CEL or any fault code. You just gotta swap in a new ICM.

If it's the Nitrogen, then I would suspect a plugged up CAT.

Had the "puffy" exhaust "kinda miss" thing turn out to be that the front CAT melted into the second and was way over on the test for Oxides of Nitrogen.

 

[sirhk100]

Interesting! I guess I'll see what the dealer says. Like I said, I was out of ideas short of just throwing parts at it.

It was high on both. Intersting thing is on Monday at idle it was WAY over on both but at RPM is just barely would've been failing. Found the bad FPR and intake air temp sensor though, replaced those and just before I took it to the dealer I had it on the same smog machine again and this time it was really close to passing at idle and now way off at rpm. We checked a couple more things and at that piont I just said screw it, dropped it off at ford for diagnostic. I'll let them tell me what's going on with it and then decide if I'm fixing it or they are.

 

[FR-425]

My money is on the ICM.

NO real way to test it that I know of, and I doubt the dealer has the specific diag tool for the 24 year old stuff anymore.

The ICM can fail into "limp" mode and not trow a code. You would notice the sudden loss of power but other that that it'll run pretty normal in limp mode. No real-time fuel/spark commands from the PCM to the ICM and NO emissions control.. Like I said it'll run, but with limited and varied results. It's meant to be just enough to get you off the road and into a shop.

When it does this there is no communication between the ICM and the PCM and therefore can not be trouble shot with OBD.

If the dealer hooks it to their ODB test and find no codes they may be at a loss if no one in the shop is savy on the older OBDI stuff.

Or worse they find a number of codes and start throwing parts at it only to fail to fix it!

 

[FR-425]

An ICM is not cheap but I would start there and if that's not it, then you will have a trail spare.

I have a "trail spare" but it has failed and is in "limp" mode. But, it will at least run well enough on it to get off the trail.

 

[sirhk100]

Excuse my ignorance here but the PCM is the one on the passenger kick panel. ICM? Ignition control module I'm guessing? Is it the one up in front of the battery right behind the passenger light?

 

[natenkiki2004]

Correct, ICM is up behind the battery. I haven't seen the PCM so I can't speak from experience.

 

[FR-425]

You got it.

PCM - kick panel

ICM - battery and yep = Ignition Control Module

 

[FR-425]

Most important!!

After disconnecting the battery, the PCM will be "reset".

The emissions control system (programming) is "adaptive".

You will need to drive the truck for at least 30 miles. Preferably with 3 drive cycles. (shut down and restart). This will "re-train" the PCM. BEFORE EMISSIONS TESTING.

With OBDII cars it will fail if the PCM reports that it is not "ready".

However with our OBDI trucks the PCM does not report "readiness", and you will still fail.

So. after you replace the ICM, or any other emissions related electronic part you will need to do this "re-training routine.

This is probably part of the reason you got such erratic results from your last test at the shop.

 

[sirhk100]

I haven't actually disconnected the battery at all during any of this process but I would assume the dealer probably will today when they look at it so good to know! I know most cars I've just typically driven them a couple exits up and down the freeway and then gone for smog so thanks for the heads up that it probably needs to be more then that.

I'm really curious to hear what the dealer says on this...

Smog is stupid, that is all I can say! I actually have to take my '02 ford diesel van to be smogged tonight too! I've got no concern with it not passing though. 100% stock and runs excellent! I've put maybe 3000 miles on it since it passed smog last year so should be good.

 

[sirhk100]

For $126, Ford diagnostics said leaking oring on fuel injector for Num 2 cylinder. They wanted an additional $480 to fix it... No thanks!!! I picked it up and grabbed a pack of orings to replace all of them and took it home. Swapped out the orings and sure enough it runs absolutely perfectly smooth now! Going to try smog on my lunch break.

 

[larrydd999]

Thanks for the report. You've finally given me a reason to go to a dealer for anything other than a part that can't be purchased any other way!

 

[sirhk100]

LOL, I'm totally with you!!!! This was the first time I"ve EVER admitted defeat and taken a vehicle to the dealer and I was a bit worried but this time around, the money was worth it in my opinion. Maybe they're not as shady as I'd always percieved!!! LOL

 

[FR-425]

Add this one to "mental" notes... . . . ..

How did it do on emish?

 

[sirhk100]

Passed but they don't give any details unless you fail so not sure how clean it passed by. Was definitely an interesting issue though. It missed enough to sound a bit rough and you could feel it on acceleration but wasn't as bad as a true missing cyl and like I said... All 6 plugs looked text book perfect.