After installation of my new, bigger cam recently my converter won't stay locked up in OD which, in turn, causes my ATF temps to creep up. Also, because of the slippage involved with the converter unlocking when it should be locked, I'm throwing two DTCs both tranny-related, P0748 - pressure control solenoid electrical and P1870 - transmission component slippage. I experience none of these problems in 3rd gear, only in OD.

Anyway, I'm pretty sure they're related to the size of the cam and the perceived misfires created by it. Anyone know of a fix? Thanks!

 

I think your problem is programming related, especially throwing the P1870 code.

 

I agree! I'm looking for the FIX!

 

The FIX involves taking your car to a tuner who knows how to program out those issues!

 

Obviously.

However, I want to know what the fix is so I can do it myself as I'm purchasing the HP Tuners software in the very near future.

 

Yikes!

P0748 indicates a continuous open or short to ground on the pressure control solenoid valve circuit. Hmmm...

The P1870 test only runs when the gear selector is in 'D' and TCC lockup is commanded, so only in 4th isn't too surprising. You can relax the test's RPM threshold limits, but you shouldn't have to - since it only runs when the TCC is commanded on you should be seeing minimum slippage (i.e. near 0) at that point.

Couple of thoughts... The service manual indicates P0748 may set in a low voltage situation. Beyond that as a potential cause, I'd look for bad/loose connections, particular those that have been apart recently. One further thought is that your programming may have line pressure too high under some conditions which I think could cause this as well. Alternatively, the PCM commands max line pressure in response to P1870 so I suppose it's possible the source of your PC solenoid code. (If this is the case, it would mean your tranny really is slipping internally.) You should be able to monitor tons of related OBD-II parameters with a scan tool, in particular the slippage. That parameter is only an esitmate but if it gradually gets worse it would suggest a non-electrical issue. OTOH, if the tranny funny business is really just a result of the misfire detection logic, there's a bunch of good info over at LS1Tech.com regarding how to disable that. However, I would only expect that to be an issue at lower RPM though and not a very likely source of issue.

Would be useful for you to have some info about your programming:
1) Changes to misfire tables
2) Changes to force motor current tables
3) Changes to your MAF table
4) and maybe changes to your TCC apply/release tables.

Now, the $64K question... Did this happen before or after the trip to the strip?

 

Before the drag strip and immediately after the latest cam installation/dyno tune. I got the codes on the drive home, in fact. Also, we did change some tranny-related parameters including some line pressure settings (higher). I really don't think it's an actual electrical problem ref. the solenoid. My guess is it's line pressure-related. However, the more serious concern, the P1870 and the converter not locking up is what I really want to address and correct. I'm guessing/hoping it's related to the bigger, 112 LSA cam as so many people have already experienced the same problem after their installations.

 

Here's a link to one of Ryan's posts. There are tons of others on the topic of misfire detection.

http://www.ls1tech.com/forums/showthread.php?t=162767

You might try disabling misfire detection altogether using the (easy) heavy-handed method first. If that clears it up, spend the time to zero in with some more selective values to get at least some detection back.

Wouldn't hurt to get the freeze frame data with your codes if possible. Curious to know which came first.

 

 

That's the kind of information I was looking for! Thanks for the help, compadre!

If nothing else, I'll either solve the problem this way or better know what I'm dealing with through the process of elimination. As I said in the other thread, I've no problem with buying a new, race-prepped tranny, but I don't want to unless it's necessary as I just can't see tossing my present one if it's still in good working order.

 

Good luck, I hope it's that simple. I agree completely about not replacing it till it really needs it (though I'd try to catch it before it blows chunks into the converter.)

 

The PCM detects misfires thru cylinder time balance the interval
of time between firing events. The overlap of the cam causes
variation in crankshaft speed. This is detected as a possible
misfiring cylinder or possibly a rough road condition. The computer will lock and unlock the torque converter going from
a fluid coupling to a mechanical lock-up to try and determine
if the condition is an actual cylinder misfire or a drivetrain, or
rough road condition. This builds heat! (Not Good)!
It also looks at ckp (crankshaft speed versus input to trans)
efficiency. You can fix with LS1 Edit by going to low rpm misfire
counter tables and putting 32767 in all cells. I would move the
lock-up to only lock-up in 4th gear at cruise speeds. Lower
the force motor amps to increase the pressure reducing friction
in the trans - Iam a trainer for techs 20 years

 

I agree though that would be the perfect excuse to get a slightly bigger converter.

 

This is VERY helpful. Thank you very much for the information!

 

Okay, I'll bite. What are you thinking about going with? And are you also thinking about a gear change? Reason I ask is I am...

 

Well, I already took car of the gear change a couple of months ago. I'm running 3.73s now and am very happy with them and their performance. Converter-wise, if I was forced to make a switch I'd go with a Yank C5 SS3200. I'm on my third Yank converter now (had a TT2800 and later an ST3500 in my '99 Camaro SS) and I've always had good luck with them.

 

Knew you had the 3.73 but thought they were much less recent. What are you thinking putting a wimpy SS3200 behind that motor? That's an old guy's converter The SS should be nice improvement w/o getting real loose.

 

As has been pointed out the most likely culprit is misfire, especially since it started to happen after a cam install. The P1870 also can be set when lower gears are installed and gear scaling is not done. It was done or you would have had the problem before. It would not hurt to check to see that at your last tune it wasn't reversed by accident. Files can be confusing.
Hope it's these easy ones and not the PO748.

 

I took a visit to see Mike/Rapid Motorsports this morning and he found the problem immediately and had it fixed in 5 minutes. LS1-Edit somehow corrupted all my part-throttle shift points (there was no rhyme nor reason to them - the values looked totally random ). Anyway, that's what was causing all the problems. I drove all the way home in OD (around a 1.5 hour, 75 mile run) and I'm happy to report the converter locked up normally and stayed locked and NO CODES!

Thanks for all your help, fellas. Just to be double-sure, we checked each and everyone of the possibilites listed here in the thread to be certain nothing was missed or amiss. Thanks again for everyone's help!