Part-throttle, min-load misfire, CLT - what's going on?

[DR1665]

Symptoms occur mostly when good and warmed up - proper operating temperature. Engine will randomly buck, drop cylinders. In the rare times it's happened while parked, idle will hunt very erratically, 500-1500rpm, before stalling. Applying ~30% throttle overcomes the issue, sometimes even "fixing" the problem for extended periods of time, but the misfires are still evident and it's not common for the car to die multiple times in a row in rush hour traffic on warmer afternoons.

Battery connections have been replaced/cleaned. Additional grounds installed. Symptoms happen irrespective of fuel level (ruling out aging fuel pump). CLT has been replaced. AC switch atop tstat housing has been rewired. Local harness exhibits typical loss of flexibility.

I'm gonna re-do all the wires this weekend, as I'm sick of this sh*t. What I'd like to know is:

- At operating temperature, lifting off the throttle in gear at approximately 3000rpm, what is the ECU looking for and adjusting? TPS, IAC, CLT?

That is, if the CLT reading is fluctuating rapidly due to connectivity issues, what is the ECU doing to try and compensate? Open/close IAC? Flood cylinders?

Don't have a logger, and the friend I usually borrow it from lent it another friend, who lent it to another friend. No access right now.

Besides, I'm looking more for an understanding of the way signals are interrelated during these conditions.

Thanks.

 

Is it like its cutting out ?Mine when it warms up at half throttle cuts ive replaced everything , im trying to figure it out . its driving me insanee

 

[DR1665]

Bumping this because it's still going on and it's really pissing me the f*** off.

It's not a boost leak. The issue only happens in vacuum and does NOT happen with any consistency. I can drive the car for a week and not have this happen. The ONLY common variable I've been able to tie to this thus far is ambient air temperature.

All sensors at thermostat housing are new and rewired. Still happens.
Low fuel/fully fueled doesn't matter. Still happens.

I'm ordering my Keyspan usb/serial adapter today and will be re-pinning my logger cable so I don't need the null modem adapter and can log on the netbook. I'm really hoping to get some more theoretical systems knowledge from you guys if you've got any ideas before I get to logging.

Last night, I got lucky and 464 started acting up just as I pulled into the driveway at home. I was able to open the door and really listen to what's going on when this happens. Idle speed will lurch up and down at random, then stall. It will not immediately re-start and idle on its own. I can keep it alive with throttle, but it sounds/feels like it's dropping cylinders, even as high as a forced 3000rpm "idle," I can still hear/feel it missing.

I can't force the fault, so I can't trouble shoot it under the hood. It's pissing me off! <img src="/ubbthreads/images/graemlins/banghead.gif" alt="" />

Anyone know of any correlation between heat and intermittent failures in the ignition or fuel system? I've seen OEM fuel pumps whig out when they overheat, but those symptoms seem pretty constant after the initial incident. Could the coil pack or transistor cause such issues? I'm not getting any codes, but could it be CAS or MAF? What about that little momentary switch on the TB signaling the throttle is closed?

I hope to be logging this sh*t within a week, but I would appreciate some insight as to what I should be looking for. The ONLY variable I can isolate thus far is ambient air temp. This does not occur when the engine is at operating temps below 60°F. Go figure.

Thoughts? Really appreciate your taking the time.

 

Well, I don't know if I can help much, but here's some things I thought of.

Is the MAS in good shape? What about the ECU? Any modifications done?

Below 60 degrees the ECU would be in open loop mode. If it only happens when it's warmed up, then it seems your problem is isolated to closed loop only. The ECU makes fueling corrections based on info from the o2 in closed loop. It would be helpful to see what your short term fuel trim does when this problem happens. Have you checked to see if the o2 sensor is good?

 

I had the exact same thing going on with 483, Mine turned out to be a coil pack and i had no CEL. Honestly though if you havnt already id go ahead and try a diffrent pair of wires, on the Mirage we were having a cutting out problem in the 5k range i know its a bit diffrent but i turned out that one of our brand new magnacore wires was bad.

Next thing i would try if it runs long enough while missfiring try pulling one of the plug wires off and see if it changes or stays the same. If stays the same could be that wire/plug/coil, May help you narrow down the problem.



Just my .02
Jesse

 

[DR1665]

Thanks for the feedback, gents. Appreciated!

MAS is good (visual). One of the first things I inspected was the condition of that guy. Cleaned it properly.
ECU is good as well. Caps replaced long ago and inspected last summer when socketed.

I don't have a logger right now, and the guy I generally borrow one from lent his to someone who lent it to someone else or something. Got my Keyspan adapter ordered yesterday and will be re-pinning my old Pocketlogger cable to log from the netbook ASAP. I'll definitely be looking at MAS and O2.

Thing is, the issue is so random - aside from ambient temps - I can't do any troubleshooting when it happens. I'd love to do a simple load balance test when it happens, but if I'm not on the gas pedal, it just dies. Balls.

Still. With the other Galant at the shop, I've got a known good coil pack in the garage. I might just swap it out for shits-n-giggles.

Thanks again, guys.

 

[DR1665]

Possibly resolved.

Finally got a logger on it and caught the bitch in the act. TPS is shorting out or something once it warms up enough. Seeing 99-100% @ idle before voltage fluctuates like mad, ECU can't keep up, engine dies. Anyone see anything like this before? I'm gonna swap the TPS here pretty quick, but I'm cautiously optimistic. :shrug

 

[ktmrider]

It's baaaaaack!

Was pretty warm on Saturday, 90's, and drove 464 across town to do some errands. On the way back home running about 60mph I could feel an ever-so-slight miss at around 3000rpm. It was very slight, just a tad bit of hesitation, almost like a fractional fuel cut. Hit the gas, problem went away. Drove another 5 miles to the house, when turning onto my street it was very pronounced. 25mph, 2nd gear, again around 3000rpm. Went to first, got the revs up to 3500, went away.

Drove it today ( 1000A ish ), again no issues until I hit about 20 miles then back the stutter came. Got worse as the heat of the day progresses. I'm back at the house and DILIGENTLY SEARCHING for some potential answers when lo and behold here is the same problem, same car LOL.

I do have a logger, will try and hook it up while monitoring the TPS signal. BD did you ever swap the TPS last year?!?

 

[ktmrider]

Well after talking in-depth with both Driggs and Toybreaker I think I found the culprit. When I hooked the emission hoses up I swapped the FPR and manifold vac lines at the FPR Solenoid. /ubbthreads/images/graemlins/banghead.gif

Log abnormality were the fuel trims, L was 140% and H was 131% with M at 105%. John had me moving vac lines around to try and toggle O2S and I noticed the FPR source vac was not there after a few mins of running. Hooked the FPR directly to the manifold, unhooked the battery, then went out for a spin. Issue appears to be gone, fuel trims on a short jaunt looked way better, after dinner I'll get a better run in and report back.

BTW does anyone know how the FPR Solenoid works? ie Cutoff or Open to Atmosphere when engaged?

 

[FlyingEagle]

FPR solenoid is going to raise fuel pressure at hot start to keep fuel from boiling.
FPR pressure goes up like when you hit WOT to atmosphere, so going to say that it will provide atmospheric pressure/vent function.