Random miss when warm

[Michael]

Now that my cold idle problem has been solved I have one more problem I want to fix. I first noticed this when charging my ac system last month after the compressor replacement. There is a random miss. It's misses very often, but there is no pattern to it that I can tell. In fact I never noticed it unless you just sit in the car and hold it at around 1500-2500 rpms where it is most prevalent. It's very hard to feel when driving but it is there under a load as well.

Now here is the thing, when it's cold in open loop it will be flawless. I can hold 2k and not one hic up. It's only when it goes into closed loop that the miss happens. The miss is there throughout the rpm range, it's just most noticeable and more common at 1500-2500 rpms.

I have checked the vacuum solenoid and it seems to be working correctly. I even unhooked the vacuum line and applied my own vacuum to the dist. advance to make sure it wasn't leaking.

So is there something that is screaming red flag to anyone? Plugs are fairly new but I have yet to pull them. I'm wondering if it running rich or lean once warmed up? Wish I had a dwell meter right now.

[Spittybug]

These are the tougher ones...... random misses like that could certainly be the ECU, but I'd be more inclined to look for cracks. Cracked plug insulation or cracks in the rotor or cap. Check your plug wires too. Make sure nothing has worn through and is shorting. A coil going bad (especially as it warms up) can give these symptoms too.

[Michael]

These are the tougher ones...... random misses like that could certainly be the ECU, but I'd be more inclined to look for cracks. Cracked plug insulation or cracks in the rotor or cap. Check your plug wires too. Make sure nothing has worn through and is shorting. A coil going bad (especially as it warms up) can give these symptoms too.

Thanks Owen. When I say "random" I mean it's always there when warm, it's just not a dead cylinder. You can hear a miss, half a second later 2 misses, 1/4 second 1 miss, runs fine for a second then misses...very sporadic but always there.

[NightFlyer]

To determine if it's related to the lambda system, you could always run it open loop by unplugging the O2 sensor and seeing if the problem persists or not.

[hmcelraft]

To me random means on a different cylinder each miss - where intermittent means the miss occurs at the same cylinder just not each time the cylinder is suppose to fire.

No misses when cold makes me think it is fuel mixture related first then, heat related activation like in wiring or fuel/air mixing.
Those related items could be - leaking fuel injector seal(s), bad or cracked spark plug, bad or loose sparkplug wire at plug or distributor cap, vacuum leak or mixed up vacuum lines at distributor and/or FPR, vacuum valve backwards, vacuum line going to fuel canister from bottom of throttle body is open -- stuff like that. From what you have said it is probably something that happened during the compressor change?

[Michael]

I disconnected the O2 sensor when warm and the miss is still just as bad. Side note, the miss is related to temp, but is there when cold too, just not as bad. It does get worse and more common when warm. I am not sure if it's the same cylinder or not but this video will help convey what I have here. In the video you can see the tach moving when holding a certain rpm level....The throttle position does not move once I hold it. You can see the rpms change and the engine straightens out for a second, then misses a few seconds(tach drops about 100rpms), then back to normal.


https://www.youtube.com/watch?v=WYqsglLrBDE

[DMCMW Dave]

I disconnected the O2 sensor when warm and the miss is still just as bad.]

Plug wires/cap etc. is where I'd start. See if you have a wire loose on the cap or plug. Usually running problems are fuel. This one sounds like ignition.

[hillbillydmc]

Hi, Sounds like it is running lean when warm, I would check the control pressure cold and warm to see if it is in spec.:biggrin:

[NightFlyer]

I like both suggestions :thumbup:

As a side, your alternator appears to be rock solid, regardless of engine RPM. Definitely not that way with the Ducey :biggrin:

[dustybarn]

I had a warm miss that turned out to be a bad ignition coil. It was pretty obvious, though, because it was leaking oil around the screw terminals.

[Spittybug]

Plug wires/cap etc. is where I'd start. See if you have a wire loose on the cap or plug. Usually running problems are fuel. This one sounds like ignition.

+1 again.

[Michael]

Thanks for all the advice. I will start looking there. I'm a bit anxious to replace the cap and rotor. Looks like the entire intake has to come off to do that.

PS Dave, I don't know if you caught the other thread but the ecu fixed the idle. I pulled it to send to you but I noticed it had been opened in the past so I opened it back up and saw a capacitor and a good bit of board fried. I knew then to just replace it without testing.

[hmcelraft]

You don't have to take off the intake if you loosen the fuel distributor and lift it some. Just be careful with the throttle plate housing or, remove the housing so it and the connecting apparatus are not strained. It is still tight to do and hard to see what you are doing at times.

[Michael]

Didn't find any loose plug ends. I think I'm going to try a coil first for two reasons.
A: When holding a certain rpm level, the times between the miss never changes. Doesn't matter if it's 1500 or 3500 it has a shot period of smooth running then a short period of stumbling and that period of time stays the same. I know my logic is not all that sound but this is about 20% of it. The other 80% lies in reason B.
B: Putting a coil on is a lot easier than a cap and I would rather throw a 50 dollar bill at it and hope that fixes it before going the cap route. I know its a gamble but the coil does look like it's seen better days.

[NightFlyer]

It is possible to do the cap, rotor, and wires without disturbing K-Jet at all, but it is a major PIA. I've personally done it twice myself now.

[Soundkillr]

Make sure the wur doesn't have vacuum on it once warm. It should when cold, but once warm it should not. If it does it would load up and run like crap. My switch went bad under the manifold, and would not switch out, causing it to load up once warm. Took me a bit to figure it out.....

[Michael]

A little update. Coil didn't fix the problem as expected but was hoping. Just ordered a cap, rotor, and a new set of wires. I have the Nology wires and I didn't want to replace them being they only had 20k on them but I have read a lot of disturbing issues with these wires. A lot of people report the same symptoms as I have and the "better" Nologies were the problem. I also didn't want to go through the trouble of replacing the cap and not do the wires.

So sometime this month I will do the relatively easy task (on a normal car) of replacing the cap. Not looking forward to this.

[sdg3205]

A little update.

So sometime this month I will do the relatively easy task (on a normal car) of replacing the cap. Not looking forward to this.

You'll be fine michael.

You really just have to remove the mixture unit. Even the w pipe can stay in place. Just take off the fuel lines and vacuum tubes

[Bitsyncmaster]

If you have that shielded high voltage wire on the ignition coil....get rid of it.

[opethmike]

The cap & rotor really aren't that. You really just need to either push the mixture unit forward, or for a little more room, remove it entirely.

A real nightmare of a job that is easy on every other car on the planet? Thermostat on my Lotus Elise - took 5 1/2 hours.

[mluder]

If you have that shielded high voltage wire on the ignition coil....get rid of it.

Why so?

[mluder]

I have been having the same problem - A intermittent miss when the engine is warn. I happened to have an extra idle control unit lying around that I picked up second hand from another owner "just in case." Turns out the pins on the connectors are different and the model number is off by one digit.

Any one ever encounter two different idle control computers?

[Bitsyncmaster]

I have been having the same problem - A intermittent miss when the engine is warn. I happened to have an extra idle control unit lying around that I picked up second hand from another owner "just in case." Turns out the pins on the connectors are different and the model number is off by one digit.

Any one ever encounter two different idle control computers?

All I've seen are 9 pin (stock) and 11 pin (turbo - 4 cyl). I don't test them but use the connector and case for my idle ECUs. They all physically look the same and the connectors will work if you pull the two "Keys" off the one connector. That still leaves one connector with one key so you can't mix up the connectors. But I would not expect a stock 4 cyl unit to work with our 6 cyl engine.

[Bitsyncmaster]

Why so?

They just cause to many problems. It was done just for AM radio reception back in the 60s. I think Noligy claimed some improvement but that was BS. Besides, it looks like hell.

[OverlandMan]

A little update. Coil didn't fix the problem as expected but was hoping. Just ordered a cap, rotor, and a new set of wires. I have the Nology wires and I didn't want to replace them being they only had 20k on them but I have read a lot of disturbing issues with these wires. A lot of people report the same symptoms as I have and the "better" Nologies were the problem. I also didn't want to go through the trouble of replacing the cap and not do the wires.

So sometime this month I will do the relatively easy task (on a normal car) of replacing the cap. Not looking forward to this.

I recently did a cap and rotor on my car, as well as plugs and plug wires. I'll reiterate that it's easiest to remove the mixture assembly completely; however, you may be able to take it loose but not disconnect the fuel lines. I can't speak to that as I just removed mine entirely since I was replacing all the fuel lines and fittings too.

Curious to know what your findings are after you replace those items. Are you replacing the plugs too? Might as well while you're in there I would think. FWIW, I ordered the Bosch plugs and wires from DPI, as well as the cap and rotor.

[Michael]

I recently did a cap and rotor on my car, as well as plugs and plug wires. I'll reiterate that it's easiest to remove the mixture assembly completely; however, you may be able to take it loose but not disconnect the fuel lines. I can't speak to that as I just removed mine entirely since I was replacing all the fuel lines and fittings too.

Curious to know what your findings are after you replace those items. Are you replacing the plugs too? Might as well while you're in there I would think. FWIW, I ordered the Bosch plugs and wires from DPI, as well as the cap and rotor.

Yeah I was told I could just remove the entire mixture unit without cracking the fuel system. I got the gasket for that coming with my order. I replaced the plugs a few weeks ago. I have a very good feeling it's those wires though.