I have done searches on the topic and the answer is not quite clear. I am about to buy a 2400-3000 stall converter PT, Yank, or possibly even TCS. P1870 slip code comes from not correctly programming in a swapped gear NOT the torque converter, right? :confused: :confused:
The TC should already be locked when the PCM is looking for discrepancy between engine speed and rear end speed? :confused: :confused:

 

The excessive slippage of the torque convertor is monitored by the pcm and the P1870 code is set along with upping the line pressure to minimize the slippage of the t/convertor. You have to program into the pcm more slippage allowance or delete the monitoring to successfully use a higher stall convertor. The C5 is the only car setup this tight. F body guys never have this problem. :cheers: :thumbs:

 

If you are going for a 3000, you might want to consider the Yank 3000. Mike there told me they are especially designed to be compatable with the C5 transmission. I am running a Yank 3000 with 3.15 gears, no programing and have not gotten any codes. Low end torqe is awsome. I really like that combination.

 

FWIW I'm running 3.73s and SY3500 with the stock P1870 test limits for a little over a year. I put them back to stock last year when the gear scaling was finally fixed in LS1-Edit. No problems of any sort.

The only reason a non-stock converter will generate this code (assuming correct gear recalibration) is if the TCC allows substantially more slip than the stock setup when locked. Yes, there could be some variance here but IMHO if it exceeds the test limits it would really indicate a poor converter design. At a minimum, the manufacturer should be able to tell you what kind of slip speeds to expect (and whether or not programming adjustments would be required.) I believe most manufacturers say programming adjustments are not necessary. As an example, Yank's warranty is in fact contingent on having a stock PCM cal.

If you know what slip speeds to expect when locked, you can measure whether or not you're meeting those expectations. Watch out for things like fluid level and line pressure adjustments (either directly through hardware or software or indirectly through screwy MAF adjustments and the like) that impact the TCC's ability to function properly.



[Modified by ToplessTexan, 8:34 AM 8/28/2003]

 

I disagree. The P1870 will be set only if the TC is malfunctioning. And that wouldn't matter if it was the stock or an aftermarket high stall variety. The "slip" is only looked when the TC is locked; so that would be either 3rd or 4th gear WHEN THE PCM has told the TC to lock. At no other times is the slip (as referenced to the P1870 code) being monitored for a failure. If the aftermarked TC is of the locking type; then it should not set the P1870 code.

Gears will set the code because the comparison between the MPH and engine RPM will be outside the norm when and only when the TC is supposed to be locked

A locking-type aftermarket TC that is not malfunctioning should not set the P1870 code (assuming the factory supplied rear axle ratio is still being used).

 

Damn he's smart. :D I agree. And if you're not using the supplied differential, you may have problems and have to reprogram the PCM. I went from 2.73 to 3.42 and had problems with the P1870 code. I think Tim went from 3.15 to 3.42 and had no P1870 problems. It's an easy programming fix.

Bob
:flag

 

So I guess most aftermarket TC are built incorrectly? :rolleyes:

Back on topic, since you have a 98, they are less prone to throw codes. You should be ok with a 3000 stall.

 

you either understand... or you don't.

And if you don't... then that doesn't make the rest of us wrong.

A non-malfunctioning TC has no slip when locked. So it doesn't matter what the stall speed of the aftermarket TC is... because... BECAUSE the PCM will only throw the P1870 code if a "locked" TC is slipping.

Make sure you aren't incorrectly using the term "Locked". Locked does not describe the RPM at which a TC "grabs". :nono:
Instead, it refers to a more modern style of TC (they started using these in the early 1980's) that actually mechanically locks the input shaft and the output shafts to each other - once commanded to do so.

Changing the rear axle ratio fools the PCM into thinking the TC is slipping; and will raise the line pressure - and eventually throw the slip code.

The C5 PCM is not looking for slip in first or second gear. Nor will it look for abnormal slip in thrid or fourth gear unless it has given the TC lock command. Only in 3rd or 4th with the TC lock command given will the PCM try to detect slip.

NONE fo this applies to F-Bodies.

Most of the streetable high stall TC's are of the locking type. In fact... it's hard to find one that doesn't lock since they have been used in new cars for the past 20 years.

.





[Modified by Mike Mercury, 4:50 PM 8/28/2003]

 

While in principle correct, that's not really accurate either. You will still see slip (difference between input and output speeds) when locked although it will be small, say 10-20 RPM (positive or negative) for example. Why? Because the lockup mechanism is pulse width modulated.

If you've got a P1870 you've got a problem. IMHO, if you're blaming your converter, you're not getting your problem solved. But that's just my opinion and worth what it cost ya. ;)

Mike B are you saying you code regularly (or did)?



[Modified by ToplessTexan, 4:09 PM 8/28/2003]

 

While locked, there is a tolerance as with everything else in this world. You must have tolerances. Nothing is perfect. The problem is when the PCM sees an out of scale tolerance. This is usually caused when we change the gear ratio in the differential. In effect, if it's locked and within tolerance it's not slipping. Although it may be. This calls for a meeting and some coffee.

Bob
:flag


[Modified by Korreck, 4:42 PM 8/28/2003]

 

We're quibbling now. :rolleyes: The only reason I'm trying to be very precise is that there is SO MUCH incorrect and misleading information on this topic archived here and elsewhere.

When the PCM commands LOCKED mode, the TCC is engaged and slip decreases to a negligible amount but it is not zero. It is slipping. My point was that it's a PWM system, not a mechanical lockup and that you cannot expect to see zero slip. That's important because if you're trying to understand how your car works you had best have some (correct) expectations up front. I'd hate to see someone pulling their hair out because they still saw 20 RPM of TCC slip speed under lockup. :banghead: I'm not trying to pick nits with Tim as I know he is correctly trying to convey the idea that slip is minimized when the TCC is locked and that the test only evaluates whether the calibration defined tolerances are being being exceeded under these conditions.

I won't even bring up the fact that the observable OBD-II slip speed parameter is only an approximation of the concept we're talking about above. :crazy:

Double mocha latte for me. :)

 

You are korrect :)

I was thinking about my 1980 Corvette and its TC did indeed mechanically lock. :bb

I had a lot of trouble with that cars lockup TC.

Thanks for getting the true facts out :cheers:

But are we all seeing that a properely working aftermarket TC should not envoke the slip code?

 

I went from 2.73's and a stock TC to 3.15's and a Yank 3000 stall converter. Ever since then I've been throwing the 1870 code...under certain conditions. First, the TCC only functions when the coolant temp is above 140 degrees and the speed is over 50 mph. The 1870 code will throw when I'm in the speed range of 55 to 75 mph. Anything above 75 - no code. Any speed below 50 when the TCC is not engaged - no code. Just in the speed range noted above will the 1870 be thrown. I'm not running any special programming except with Hypertek for coolant temp fan turn -on points.

Book says the following has to be met before the 1870 code will throw:
- Vehicle speed is 35 - 65 mph
- Speed ratio is .67 - .9 (determined by dividing engine speed by output speed
- Engine speed is 1200 - 3500 RPM
- Engine torque is 40 - 400 lbs ft.
- Gear range is D4
- Not in 1st gear
- TCC is commanded on for 5 seconds
- TCC is at maximum apply for 5 seconds
- TCC slip speed is 150 - 800 RPM
- All conditions met for 7 seconds
There are other conditions mentioned such as other codes being set but I never throw any other codes. If other codes are thrown along with the 1870, the book seems to suggest a component failure such as TCC solenoid valve, faulty sensor, etc. Just an 1870 code alone along with the fact that other people going to a stall converter over stock have been experiencing this phenomena but not before doing the mod suggests to me that its just one of those quarky things that goes along with the mod but can be remedied through proper programming. With the tight specs in the stock programming on these cars, I would think ANYONE going to a high stall converter would throw the code but that apparently is not the case. After all, thats what a stall converter does is slip, isn't it? I know there's a little more to it than that so I'll leave the debate for you more knowledgable fellas.
I'm just glad I'm running an FLP Level 4 tranny so that extra line pressure that is commanded every time the 1870 code is thrown doesn't affect me. One of these days, I'll break down and get an LS1-Edit or travel a 100 miles to Ed Wright and let HIM reprogram to take care of that annoying code. :cheers:





[Modified by MikeyD, 11:29 PM 8/28/2003]

 

I hope so, I want to put off buying LS1 Edit until I get into more serious mods. :yesnod:

 

If all you're planning is a small converter with stock gearing you should be fine from a DTC perspective... Unless you have a funky MAF configuration and then all bets are off. ;) In general, things that affect line pressure are candidates for causing you grief.

MikeyD, have you considered pulling and shipping him your PCM?



[Modified by ToplessTexan, 8:28 AM 8/29/2003]

 

MikeyD

great info :cheers:

 

Kurt,

The only MAF mod I have include a hand port / polish and a MAFT. Do you think I will still be okay. :confused:

Thanks for everyone's help. This is a subject that is not quite clear to everyone and answers seem to vary depending on model year.

 

if you look at the "books" specifics; here is the order in which the PCM will
set the P1870 code:

*Vehicle speed is 35 to 65 mph
this makes sense with those reporting the P1870; who notice it happening
during highway driving.

*Gear range is D4
*Not in first gear
Why would the spec first say "D4" but then state "not in 1st gear"
By the "D4" line, they are not saying that the slip is only detected
in 4th gear... but instead are saying
"anytime the TC is locked (in any gear) if the gear selector is in Drive". And since the TC lock is only commanded in 3rd and 4th gear; then it will only try to detect slip in third and fourth gear - with the gear selector in "D" - and the TCC lock command sent.

If this is all correct, then driving around with the gear selector in "3"
will not pop the code.

I'm surprised it doesn't say "Not in first or second gear" because on my
2002 the TC will not lock in second ???

*TCC is commanded for 5 seconds.
This verifies the fact that slip detection does not occur unless the TC
is supposed to be in the locked condition.

*TCC is at maximum apply for 5 seconds
Here is the raised line pressure requirement; and explains why many feel
the hard shifts before the P1870 code will be thrown.

This listing of events may be the earlier PCM program found in 1997 to
2000 C5's. Part of the 2001 major rewrite was to minimize codes being
set, and certain parameters were relaxed. I do believe that on 2001 and
newer C5 A4's the "max apply" time was lengthened quite a bit... making
it take longer to set the P1870.

*TCC slip is 150 - 800rpm
This is the first time I have seen the actual RPM slip figures. I do
have a table that shows the allowable slip range, but it is in
percentage... not rpm.

and this explains why changing the rear axle ratio will set the P1870.
Lets say your properly operating 2.73 has 100 rpm slip (below the 150 rpm threshold) at TCC lockup when cruising down the highway at 2200 engine rpm . If you change to the 3.15 ratio... the new engine rpm will be
- roughly - 2500, and this increases the "perceived" slip another 300rpm; to a total of 400 rpm (although in reality there is still only 100 rpm's being "slipped").

The "slip" is calculated by comparing the vehicle speed sensor data (located in the rear carrier) - comparing it to the engine rpm. Thta is why the "calculate" slip in the above example will be increased by 300rpm.


Also you can see that any aftermarket TC that is lockable (and not
malfunctioning) should keep the slip rpm's below the code threshold.
With the TCC locked - an aftermarket TC should not function any different
than the stock converter.


Hey, I'm the first to say book smarts don't always mimic real life; but
this seems to all add up to what many have experienced.


.


[Modified by Mike Mercury, 11:32 AM 8/29/2003]

 

You are correct regarding the "leave it in 3" trick as a way of avoiding the code, at least around town where you don't need OD.

Once upon a time I worked through the math on the slip errors that result from running different gears with no cal changes. It's proportional to the difference of the ratios.

bats, it's exactly that sort of MAF mod that I'd stay away from. Have a peek in the service manual's auto transmission section for the TAP cells and you'll see why. (Some places they are described as being indexed by torque, others by TPS. Who knows which is correct... :cuss) I understand the goal of fuel trimming via MAF signal manipulation but I've never really been a fan (although I do have my own collection of various MAF parts collecting dust.) I'm an advocate of using the injector flow rates to deal with this, but I think even that is a hack (although one with less global impact.)