Engine Misses when Hot. Need help.

SA · 02-07-2001, 10:49 PM

I need your help.

For the past few weeks my car has been missing. This only occurs when the car is warm-hot (~190-200 deg) and the engine only misses on the driver side bank (cylinder balance test verified).

This is how it starts-
I start the car in the morning. All is well. I drive to my destination (~15miles) and all is still good. Temp is about 180.
I shut the car off and restart it a few hours later and take off. I hit traffic and the temp rises to around 195, I turn my fan on and the temp drops to 180 or below. If I drive for, say, an hour like this (hot, cool, hot, etc, etc), the car starts to miss. All of a sudden –like at a stop light.
I drive it home, where I leave it to cool for a few hours. Once it's stone cold, I start it up and no problems.

This has never happened to me before. It all started when I re-did my heads (FYI -not my first time doing this). I don't think that it's anything small like a vacuum leak or a bad wire(s) or cap because it ONLY happened when it gets into closed loop (or open loop –I forget. Whichever "loop" occurs once the car is warm).

As I stated above, I have verified that the driver side bank is the one that is missing and it spits out a lean code, BUT again it only misses when it's hot (I've done the test when the engine is cool and no codes)

I remember using a magnet to pick up a bolt that fell in my driver's side h-pipe pipe. It wasn't too strong, but maybe that screwed up that side's oxygen sensor? Would a bad oxygen sensor cause a miss like this? Any way to verify?

Could bad lifters cause this? I have a "new" tick coming from the top end that I didn't have before. It's not the regular "sowing machine" sound. More like two spoons hitting each other. It starts around 2000rpm and progresses from there. I thought it was the injectors, so I bought some new ones (I needed the upgrade anyhow). I replaced the injectors today and still no luck. Mind you, power is great when it's cold -it pulls to the moon and back. :-)

I'm stumped. The thing that really throws me off is that is only happens when the car is hot.
I bought some new spark plugs today and will be installing them tomorrow (which I doubt will help). My guess it that it's something electrical.

O, almost forgot, could a bad coil do this? I would imagine that it would always miss (hot or cold) if I had a bad coil. I also have a MSD 6AL and a Vortech BTM (blower is not on though). I'll try bypassing these to see if these are the cause.

What do you think it is???

90dpscoupe · 02-08-2001, 12:13 AM

Ok, this happened to me before, and i think it was the TFI, but you would find it on a scanner, but, i would check the coil wire boot, like on the coil part, my wire was turned into ash, but couldnt see it until close inspection, hope you fix it....good luck

Do you have a FPR? and also check computer ground, how many miles on the car?

------------------
90 lx coupe: Mac cold air fenderwell, accel supercoil,advncd ignition,3-core radiatr, FMS alum D/S, Black magic fan, 3.27grs, 3chbr flows.
Best time: 13.9116(on 225/60/15 firehawks)
Best mph: 97.80
Best 60': 2.0047

next mods: subframes, mac h-pipe

SA · 02-08-2001, 12:32 AM

Thanks for replying.

So your saying that you also had this condition –engine missing only when hot?
So what was it? The TFI or the coil wire, or both?

I do have a fpr and the engine has about 70K miles. All grounds are there and them some. heh.

I have been trying to solve this dilemma for a month now. I'm growing tired. Ugh.
Key point is that it ONLY happens once the car is warm.

thanks again

90dpscoupe · 02-08-2001, 02:20 PM

Well, usualy the 02,s act up when the motor is hot, only when they're bad, but the tfi's are defective devices when they get hot, but would probaly stall the motor too. a scanner would find the 02 problem, and the tfi might not come up on a scanner unless it's hot.

I'll keep posted if i suggest it's anything else

spinemup · 02-08-2001, 02:37 PM

change the tfi

Super9089 · 02-08-2001, 05:11 PM

I had a skip/miss when warm & it was corrected when I changed the module on the distributor. I don't claim to be a mechanical wizard but thought it may be worth a look. I also changed the pick up inside the distributor.

Dangerous Dave · 02-08-2001, 05:49 PM

I had similar problems. When the diagnostic computer said one bank was running lean when hot, I changed the 02 sensor and that took care of the problem. Kinda weird but a couple weeks before that I felt a miss when it was at normal operating temp and I woul dlet it pull past 3500 rpm's. I changed the TFI and then no problems. I would say it is the TFI but since it is saying that one bank is running lean the 02 sensor is what controls that. I would put money on the o2 sensor being the culprit. The TFI module controls the spark-not fuel. the only way for the computer to tell that the left bank is running lean is through the exhaust gases measured by the o2 sensor.

------------------
1988 GT-under construction

Dangerous Dave · 02-08-2001, 05:57 PM

I chased this problem for 3-4 months before I changed those 2 things and I never had anymore problems. People told me it could be the coil, the fuel pump, the TPS, the spark plug and coil wires, anything, and I wasted alot of money on replacing parts that were not in need of being replaced.

As for your ticking problem...when you installed the heads-did you adjust them properly? If they are pedestal mount, then did you check to see if you needed any shims? I guess from what you explain it sounds like the valve train is out of adjustment.

SA · 02-09-2001, 01:44 AM

Sorry for not replying sooner. I've been working on the car all day.

I have switched caps, rotors, wires, and plugs. Played with sensors, wires, grounds, etc. Same thing.
I have yet to switch the o2s –will do it tomorrow.

But here's the thing. When I replaced the cap, the plugs on the cap that match up with the driver side bank were black, that is, the dielectric compound was black in color. I thought this was strange, so I cleaned all of the cap plugs off and tried cleaning the wire ends too. I did not add more compound

Anyways, I take the car out, get it hot, play with the fan, the usual routine –and the missing never appeared.

I don't want to get my hopes up, but I think that was it –the dielectic compound.??
I used the regular cheap stuff at the local auto store. I don't have a clue why this did what it did, if it was doing it at all.
I'll also be getting some new spark plugs wires asap (even though I checked that are out).

Next, the TFI unit. I switched distributors with a bud and no change in condition. I was faily confident that my dist/TFI units were good, but I checked anyway.

I re-did a code check again and came up with, of all things, a 29 (KOEO). The VSS. I've never had this one before. I don't have an auto trany nor cruise control, so it's probably messing with the idle-air bypass. Hum. I'll redo a test tomorrow.

On the cylinder balance test, I came up with an 8, and only an 8 for both the 65% and 43% drops. Before, I used to get the 8 in both too, but also got 5 and 6 with the 43% drop.
I isolated the #8 wire from a potential ground and have yet to re-test.

I'll drive it a lot tomorrow before dicking around with it again. If all's well, I'll just leave it alone and see what happens.

Dangerous Dave,
The rockers are correctly installed. I have gone through the adjustment many times with my heads. It's just that this time, there is a different sound that comes up around 2000rpm and up.

My rockers are stud mounted. I have side to side play in my FMS rockers (uninstalled). I believe that this play within the rockers and the angle of my valves (/////// instead of the regular lllllll) is what makes the regular sewing machine sound (of which I've had since day one, years back), but the clacking/tapping sound is what has me thinking.

Power has not dropped at all and vacuum is strong and steady.
Maybe it’s the different brand head parts I used this time (different harmonics)? It's weird. It kind of sounds like bad lifters, but wouldn't power be down?
hum.

Thanks all for the help. I'll keep working on it and give you guys updates.

02-07-2001, 10:49 PM	#1
SA Registered Member Join Date: Apr 1999 Posts: 14	Engine Misses when Hot. Need help. I need your help. For the past few weeks my car has been missing. This only occurs when the car is warm-hot (~190-200 deg) and the engine only misses on the driver side bank (cylinder balance test verified). This is how it starts- I start the car in the morning. All is well. I drive to my destination (~15miles) and all is still good. Temp is about 180. I shut the car off and restart it a few hours later and take off. I hit traffic and the temp rises to around 195, I turn my fan on and the temp drops to 180 or below. If I drive for, say, an hour like this (hot, cool, hot, etc, etc), the car starts to miss. All of a sudden –like at a stop light. I drive it home, where I leave it to cool for a few hours. Once it's stone cold, I start it up and no problems. This has never happened to me before. It all started when I re-did my heads (FYI -not my first time doing this). I don't think that it's anything small like a vacuum leak or a bad wire(s) or cap because it ONLY happened when it gets into closed loop (or open loop –I forget. Whichever "loop" occurs once the car is warm). As I stated above, I have verified that the driver side bank is the one that is missing and it spits out a lean code, BUT again it only misses when it's hot (I've done the test when the engine is cool and no codes) I remember using a magnet to pick up a bolt that fell in my driver's side h-pipe pipe. It wasn't too strong, but maybe that screwed up that side's oxygen sensor? Would a bad oxygen sensor cause a miss like this? Any way to verify? Could bad lifters cause this? I have a "new" tick coming from the top end that I didn't have before. It's not the regular "sowing machine" sound. More like two spoons hitting each other. It starts around 2000rpm and progresses from there. I thought it was the injectors, so I bought some new ones (I needed the upgrade anyhow). I replaced the injectors today and still no luck. Mind you, power is great when it's cold -it pulls to the moon and back. :-) I'm stumped. The thing that really throws me off is that is only happens when the car is hot. I bought some new spark plugs today and will be installing them tomorrow (which I doubt will help). My guess it that it's something electrical. O, almost forgot, could a bad coil do this? I would imagine that it would always miss (hot or cold) if I had a bad coil. I also have a MSD 6AL and a Vortech BTM (blower is not on though). I'll try bypassing these to see if these are the cause. What do you think it is???

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02-08-2001, 12:13 AM	#2
90dpscoupe Registered Member Join Date: Jun 2000 Location: sanantonio, Tx, usa Posts: 1,407	Ok, this happened to me before, and i think it was the TFI, but you would find it on a scanner, but, i would check the coil wire boot, like on the coil part, my wire was turned into ash, but couldnt see it until close inspection, hope you fix it....good luck Do you have a FPR? and also check computer ground, how many miles on the car? ------------------ 90 lx coupe: Mac cold air fenderwell, accel supercoil,advncd ignition,3-core radiatr, FMS alum D/S, Black magic fan, 3.27grs, 3chbr flows. Best time: 13.9116(on 225/60/15 firehawks) Best mph: 97.80 Best 60': 2.0047 next mods: subframes, mac h-pipe

02-08-2001, 12:32 AM	#3
SA Registered Member Join Date: Apr 1999 Posts: 14	Thanks for replying. So your saying that you also had this condition –engine missing only when hot? So what was it? The TFI or the coil wire, or both? I do have a fpr and the engine has about 70K miles. All grounds are there and them some. heh. I have been trying to solve this dilemma for a month now. I'm growing tired. Ugh. Key point is that it ONLY happens once the car is warm. thanks again

02-08-2001, 02:20 PM	#4
90dpscoupe Registered Member Join Date: Jun 2000 Location: sanantonio, Tx, usa Posts: 1,407	Well, usualy the 02,s act up when the motor is hot, only when they're bad, but the tfi's are defective devices when they get hot, but would probaly stall the motor too. a scanner would find the 02 problem, and the tfi might not come up on a scanner unless it's hot. I'll keep posted if i suggest it's anything else

02-08-2001, 02:37 PM	#5
spinemup Registered Member Join Date: May 2000 Location: middleboro,ma, usa Posts: 734	change the tfi

02-08-2001, 05:11 PM	#6
Super9089 Registered Member Join Date: Feb 2001 Location: Coventry R.I. U.S. Posts: 37	I had a skip/miss when warm & it was corrected when I changed the module on the distributor. I don't claim to be a mechanical wizard but thought it may be worth a look. I also changed the pick up inside the distributor.

02-08-2001, 05:49 PM	#7
Dangerous Dave Registered Member Join Date: Sep 1999 Location: Minneapolis, MN Posts: 121	I had similar problems. When the diagnostic computer said one bank was running lean when hot, I changed the 02 sensor and that took care of the problem. Kinda weird but a couple weeks before that I felt a miss when it was at normal operating temp and I woul dlet it pull past 3500 rpm's. I changed the TFI and then no problems. I would say it is the TFI but since it is saying that one bank is running lean the 02 sensor is what controls that. I would put money on the o2 sensor being the culprit. The TFI module controls the spark-not fuel. the only way for the computer to tell that the left bank is running lean is through the exhaust gases measured by the o2 sensor. ------------------ 1988 GT-under construction

02-08-2001, 05:57 PM	#8
Dangerous Dave Registered Member Join Date: Sep 1999 Location: Minneapolis, MN Posts: 121	I chased this problem for 3-4 months before I changed those 2 things and I never had anymore problems. People told me it could be the coil, the fuel pump, the TPS, the spark plug and coil wires, anything, and I wasted alot of money on replacing parts that were not in need of being replaced. As for your ticking problem...when you installed the heads-did you adjust them properly? If they are pedestal mount, then did you check to see if you needed any shims? I guess from what you explain it sounds like the valve train is out of adjustment.

02-09-2001, 01:44 AM	#9
SA Registered Member Join Date: Apr 1999 Posts: 14	Sorry for not replying sooner. I've been working on the car all day. I have switched caps, rotors, wires, and plugs. Played with sensors, wires, grounds, etc. Same thing. I have yet to switch the o2s –will do it tomorrow. But here's the thing. When I replaced the cap, the plugs on the cap that match up with the driver side bank were black, that is, the dielectric compound was black in color. I thought this was strange, so I cleaned all of the cap plugs off and tried cleaning the wire ends too. I did not add more compound Anyways, I take the car out, get it hot, play with the fan, the usual routine –and the missing never appeared. I don't want to get my hopes up, but I think that was it –the dielectic compound.?? I used the regular cheap stuff at the local auto store. I don't have a clue why this did what it did, if it was doing it at all. I'll also be getting some new spark plugs wires asap (even though I checked that are out). Next, the TFI unit. I switched distributors with a bud and no change in condition. I was faily confident that my dist/TFI units were good, but I checked anyway. I re-did a code check again and came up with, of all things, a 29 (KOEO). The VSS. I've never had this one before. I don't have an auto trany nor cruise control, so it's probably messing with the idle-air bypass. Hum. I'll redo a test tomorrow. On the cylinder balance test, I came up with an 8, and only an 8 for both the 65% and 43% drops. Before, I used to get the 8 in both too, but also got 5 and 6 with the 43% drop. I isolated the #8 wire from a potential ground and have yet to re-test. I'll drive it a lot tomorrow before dicking around with it again. If all's well, I'll just leave it alone and see what happens. Dangerous Dave, The rockers are correctly installed. I have gone through the adjustment many times with my heads. It's just that this time, there is a different sound that comes up around 2000rpm and up. My rockers are stud mounted. I have side to side play in my FMS rockers (uninstalled). I believe that this play within the rockers and the angle of my valves (/////// instead of the regular lllllll) is what makes the regular sewing machine sound (of which I've had since day one, years back), but the clacking/tapping sound is what has me thinking. Power has not dropped at all and vacuum is strong and steady. Maybe it’s the different brand head parts I used this time (different harmonics)? It's weird. It kind of sounds like bad lifters, but wouldn't power be down? hum. Thanks all for the help. I'll keep working on it and give you guys updates.