Well Im stumped. Code 24, 35 and missing badly only after hot starts

[GC89]

I all of a sudden have a code 24 and 35 and the car will miss very badly after hot starts. I have to drive for a good 20-30 minutes it seams like and then shut the car off and when I start it again it runs like shit and misses. Litteraly sounds like a subie and will run like this from there on out. If I let it cool down for quite a while (>3 or 4 hours) it will start back up fine and be normal. The other strange thing is it doesnt seem to let me clear these codes. I pulled the efi fuse for over a minute twice and and both times there they were before even turning the car over. I have tried changing the ait sensor, putting a 2.2k resistor between THA and E2 on the AFM plug (already have one wired in at ecu plugs) and even straight jumping them and it doesnt change anything. I dont know if the code 24 is even my problem, sounds like others have had it without issues other than an annoying code. Next I was going to check the resistor I wired in between THA and E2 right at the ecu plugs, maybe the resistor is overheating and giving screwy values??? Im really getting stumped, I have messed with several other sensors and wires and cant figure anything out. All I can figure is something is getting heat soaked and throwing bad values. I also check spark while it is doing this and it was at all plugs and good. Timing was jumping around a few degrees though?
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TWINS

 

[black91turbo]

Not insluting your intelligence but did you remember to wire the maft-pro with HAC modified ECU diagram? My resistor is at the AFM plug and it works fine.....My thought was maybe that HAC code is also causing the 24? Sorry bud im not well versed in the HAC system but those are just some suggestions.

 

[GC89]

Yep hack mod is wired in, I should have also mentioned that the car has been running perfectly on the maft pro for 6 months. I havent changed anything just did a hg and put it back together and now this. Its not pulling fuel or spark so All I can figure is the timing. I think something is causing the ecu to pull timing way back and erratically and this is a causing the missing. Any other ideas?

 

[GC89]

Ok so I left the efi fuse out OVERNIGHT and put it back in, put the diag jumper in place and as soon as I turn the key I get 24 and 35. What would cause it to not even let me erase the codes??? Im pretty lost at this point, Paging Jet Jock

 

[jetjock]

Neither of those codes should cause missing. That said the ECU is not going to clear them as long as the faults still exist. And you can't just jumper a sensor. The ECU will read that as a short and set the appropriate code.

"Next I was going to check the resistor I wired in between THA and E2 right at the ecu plugs"

^ This is smart. Do it. Either unplug the ECU connector and measure resistance or leave it plugged in and measure voltage. If voltage it must fall between 100 mv and 4.8 volts for the code to be cleared.

 

[GC89]

If the resistor is returning the wrong value to the ecu that would cause the codes but still shouldn't cause the miss correct? What will cause the ECU to pull timing badly?

 

[jetjock]

The ECU doesn't read resistance directly from those sensors, it reads voltage based on the resistance. Therefore if the resistance is wrong the voltage will be wrong.

If it's wrong enough to cause the voltage to fall outside the above mentioned limits a code will be set and a default value will be used to operate the EFI system. If the resistance is wrong but results in a voltage that falls within those limits no code will be set and the engine will operate based on the incorrect signal. Generally speaking such "shifted sensors" are likely to result in worse driveability symptoms than those which set codes.

Regardless of which form a sensor's signal takes the only way to know if it's working correctly is to check at the ECU connector and see if the signal being presented to the ECU accurately reflects the physical variable that sensor is supposed to be measuring.

 

[GC89]

I checked the voltage and the resistance and found that it doesnt look like I ever put a resistor between THA and E2. I confirmed this with the multimeter and there is no connection between the two. If I test at the afm plug with the key on I get 2.51v between the two. If the range is 100mv and 4.8v I assume the ecu puts out 5v, so I am baffled as to why I would only be getting 2.51 at the plug. Its been well over a year since I wired in the maft pro so I am going to check all my wiring and make a diagram of how I did it because there are variations. I was sure I used a resistor to simulate air temp because I remember reading that 2.5k simulated about 60 degrees and I drive the supra mainly in the summer so i went with 2.2 to simulate a warmer temp.

 

[grimreaper]

2.5 is colder, i run a 1.2K because ambient has been in the high 90's lately.

 

[GC89]

It looks Like I must have used Vo to supply a signal to THA instead of a resistor. I'm still stumped on why the 24 and 35 have popped up all of a sudden. I am wondering if my ignitor could be the source of the missing when hot. I have it located down on the frame rail under the intake and it seams to get pretty warm. Drove until warm, shut it off and then started again right away and it ran fine then I let it sit for 5 min and tried again and there was the Stumbling and miss. I put an Ice pack on the ignitor and no matter how cold I got it the miss was still there. Should I track down another ignitor or look at other things? What sensor are there that have an affect on timing?

 

[GC89]

I finally got a chance to borrow an ignitor today and it didn't make a difference. I took it for a drive untill fully warm and then let it sit for 2-3 minutes. After starting it again it was missing. Swapped ignitors and absolutely no change. JJ is there anyway the code 24 and 35 could even contribute to this? What sensors have the ability to affect timing and ignition?

 

[JimR]

Make sure your maftpro v-out is not still hooked up to THA. That would seriously mess with the voltage readings. When doing the THA-E2 resistor mod, you disconnect the original v-out wire from the maftpro. Same applies to the HAC voltage divider resistor mod.