One for the experts

[02_TruBlu]

Problem: Engine has random misfires, no torque below 3k (have lost ~4 mpg), and as seen by looking at spark plugs, appears to be running lean. Have 57k miles.

The car has been at my buddies shop a few times and that is all the computer can tell him is that I have random misfires, no other codes such as crank sensor or O2's. Ford even sent him a flash for the car and it hasn't helped. Most of the time the light comes on when I am barely on the gas, just coasting. The other day it did blink for about 10-20 seconds when it came on. Short term and long term fuel trims look good.

My mods: Steeda CAI (has been on for at least 20k) and pullies (30k).

Fuel filter and Plugs have about 7k on them. MAF sensor has been cleaned a few times. Cylinder compression was good.

Anyone experience this before? Any ideas?

 

[RandyStinchcomb]

I'd have to say you have 1 or more COP's going bad. also wth todays blends of "street" fuel, its hard to get a good plug reading as wth all the adtives in the fuel today will make the plugs appear white. only way to-do a plug check right is to make a blast and cut the engine clean, kinda hard to-do on a street car nowadays.

 

[1fast03pony]

I'd have to say you have 1 or more COP's going bad. also wth todays blends of "street" fuel, its hard to get a good plug reading as wth all the adtives in the fuel today will make the plugs appear white. only way to-do a plug check right is to make a blast and cut the engine clean, kinda hard to-do on a street car nowadays.

thats what it sounds like to me. Check the COPs

 

[cooter_11]

Sounds like you may have gotten a bad batch of gas if the COP's check out ok.

 

[jstreet0204]

Random misfire codes can be tough, since there are so many things that can cause them. Something else to check would be your crank bolt. Make sure it is torqued to spec. This will cause misfires if it is even if the balancer has only moved slightly. Good luck with it...

 

[02_TruBlu]

I'd have to say you have 1 or more COP's going bad. also wth todays blends of "street" fuel, its hard to get a good plug reading as wth all the adtives in the fuel today will make the plugs appear white. only way to-do a plug check right is to make a blast and cut the engine clean, kinda hard to-do on a street car nowadays.

I had #3 replaced around 35k. But there was a code that said that cylinder. Do you think that all 8 went bad at once? I watched the MDS and it really was random misfires, all banks. The computer may clear itself and then maybe after 50-70 miles, SES is back on.

"Sounds like you may have gotten a bad batch of gas if the COP's check out ok."

Don't think so only for the fact that I have been through many tanks, different stations and used all grades since this started happening.

Now the crank bolt reply interests me for it is something that I have feared. What happens if the crank bolt isn't properly torqued? It is keyed, so the pulley shouldn't slip on the crank. When I put the Steeda pulleys on around 20 some thousand miles, I screwed up and stripped the crank threads. Had my buddy finish the job and put the crank pulley on, but there has always been a worry about it since. So if it is the bolt/pulley, shouldn't my light be on constantly?

 

[jstreet0204]

Now the crank bolt reply interests me for it is something that I have feared. What happens if the crank bolt isn't properly torqued? It is keyed, so the pulley shouldn't slip on the crank. When I put the Steeda pulleys on around 20 some thousand miles, I screwed up and stripped the crank threads. Had my buddy finish the job and put the crank pulley on, but there has always been a worry about it since. So if it is the bolt/pulley, shouldn't my light be on constantly?

The crank pulley is keyed, so it won't slip around the crank, but if the bolt isn't torqued down right, it will allow the crank trigger for the cps to float back and forth causing misfires. If some of the crank threads are stripped it can be helicoiled. I had the exact same thing happen to me. The kit is about $75 at napa, and I had to get the drill bit at lowes. As far as the light being on consistantly, no. The trigger can ride in the right place for a while then slip back and forth periodically. I'd bet that this is your problem.

 

[Gearbanger 101]

I'd look into the TPS sensor as well. Random low RPM misfires under light pedal is often a sign of a bad throttle position sensor.

 

[Dan_Soprano]

could be a host of things, like gearbanger said, the TPS, also could be the EGR or a vacuum leak.

 

[Superhereaux]

my guess is the egr



it affects all cylinders so random misfires can definately be a problem

 

[DBMSTNG]

if it was running lean, the car should be running hotter and if anything, have a little more power. i'm guessing it's running rich. that would explain the low end loss and the decrease in gas mileage.

bad COP's only throw and engine code if the miss over 2 or 3% of the time.

 

[02_TruBlu]

could be a host of things, like gearbanger said, the TPS, also could be the EGR or a vacuum leak.

Thanks for the input thus far fella's. I checked the TPS and sure enough, it was less than 8 volts. Adjusted it, light went off this morning. Will see if it holds out. But if anything, I can feel my low end is back. I don't know anything about the EGR, so does anyone have a link handy to point me the way for learning/adjusting (if it gets adjusted)?

 

[Gearbanger 101]

Damn I love being right.

 

[02_TruBlu]

Damn I love being right.

Not so fast Gearbanger. To correct myself and as not to confuse others, the TPS was less than .8 volts. BUT, even though I kept my bottom end, my light did come back on today, about 60 miles traveled before it happened. Curiously, it came back at the same spot/distance as a few times before, down a hill on the way back home. What does that mean, nothing, but interesting. Might just have to buy myself a Xmas present and buy a Predator/XCalibrator or Sniper tuner so that I can log data. My inspection is due next month, so if I can just keep the computer cleared for 100 miles my buddy can pass it and we can just continue on with diagnosing this problem as time (and $$$) permit.

Any other idears?

 

[RandyStinchcomb]

yeah, TPS voltage re-sets itself everytime you start the car ne-way. I still say its a COP problem.

 

[02_TruBlu]

yeah, TPS voltage re-sets itself everytime you start the car ne-way. I still say its a COP problem.

If so, how would you go about this Randy? Would you replace all 8 at once? What does a set go for btw?

 

[exindust]

COP's are pretty expensive... to do all at once would be costly i think they are like 60-90 bucks per COP. You could buy 2 COP's or one for that matter and check 2 cylinders at a time. It may take a long time to figure it out but if you get through all 8 cylinders and the problem hasnt gone away by testing 2 by 2 by 2 by 2 then you probably have a bigger issue.

 

[Gearbanger 101]

Not so fast Gearbanger. To correct myself and as not to confuse others, the TPS was less than .8 volts. BUT, even though I kept my bottom end, my light did come back on today, about 60 miles traveled before it happened. Curiously, it came back at the same spot/distance as a few times before, down a hill on the way back home. What does that mean, nothing, but interesting. Might just have to buy myself a Xmas present and buy a Predator/XCalibrator or Sniper tuner so that I can log data. My inspection is due next month, so if I can just keep the computer cleared for 100 miles my buddy can pass it and we can just continue on with diagnosing this problem as time (and $$$) permit.

Any other idears?

Does it still have random missfires and no torque below 3,000rpm, or is it now just the light on the dash that's on? If it's just the light, you probably just need to go to the dealer and have the codes cleared from the system.

 

[jstreet0204]

I still think it is the crank bolt. Too much of a coincidence that you stripped the crank bolt. Like I said I've been through the exact same thing. Whatever it is, good luck with it.

 

[02_TruBlu]

The light came back on. No doubt I am still having the random misfires. The TPS adjustment cured my loss of low end when I am not misfiring, but whatever the problem is, it is still there.

Whether you are right or wrong jstreet0204, it is something I need to be sure of. I mentioned it to my buddy tonite and he said he can do it if I want. Should be cheaper than buying a programmer or a set of COPs right now.

Anyone wanna steal an 02 True Blue GT complete with 18" FR500 wheels?