VikingTrad3r

Hi guys.

I'll save you all the history recap but suffice it all by saying that my tc is locking up immediately in 2nd, 3rd, and 4th. Creates engine lugging and is unenjoyable to drive compared to my 87 which does not exhibit any of this behavior. this is the second transmission in this 85 to exhibit this behavior. i can rule out the transmission/tc as the cause for this.

The shift into 2nd is made and then boom the tc engages with a nice lug-lug-lug as if somebody popped the clutch on a manual trans but far too soon (low rpm).

Unplugging the tcc wiring on the case, and the car shifts aabbssooluuutteellyyy beautiful. It did the same thing on the previous transmission, perfect shifting without the tcc harness plugged into the case.



The research I have done indicates the following sensors contribute to the ecm sending the lockup signal to the tcc solenoid:

Vehicle Speed Sensor (VSS)
Throttle Position Sensor (TPS)
Coolant Temperature Sensor (CTS)
overdrive switch mounted inside under the center console trim plate brake switch (the same one that lights the brake lights)

other participants in the tcc lockup sequence are: (there might be more)

wiring harness from the ecm to the tcc solenoid

ecm itself


prom tune itself maybe is telling it to lockup too soon, anybody know what the stock 85 prom chip was set for locking up tc at rpm values in different gears?



(this information was provided by http://www.corvettebuyers.com/c4vettes/tcc.htm )


Testing:

brake switch - I have tested the brake switch in that I can get the tc to unlock while driving by pressing gently on the brakes. so passed.

coolant temp sensor - (the one under the tb) I installed a new coolant temp sensor with no change in the tcc lockup behavior.

tps - i have it set to 54mv. no dead spots. seems to work great.

vss - i see no issues on the *dash* with respect to th vss. i just had the tailshaft housing off this trans and there were no issues mechanically to report.



awaiting testing:

i have not tested or even looked into the overdrive switch yet.

i have not inspected the harness for the tcc solenoid from the ecu, which is too bad, because i just had this trans out.

i have no inspected the ecu.

prom chip - i do not have the required equipment to check the tune. but i could pull the chip and verify it is the OEM 85 chip i suppose.


other anecdotal observations that may prompt ideas:

- idle, everything, running absolutely perfect, this car has never run better. this **leads me to believe** that the sensors (cts, tps) are functioning. everything about this 85 has been fixed, but the tcc still engages too soon.


- NEVERMIND THIS POINT. 85 does not have an "upshift light". I read from a post by Cliff Harris, that the upshift light uses the same parameters to come on as the tcc engagment conditions. for what its worth, i NEVER get the upshift light come on in my 85. Never seen it. I see it all the time in my 87.


- the car does throw a code 32 on cold start which i have verified is the egr temp switch which i am not very surprised about because when i disassembled the engine for rebuild the porcelain housing for the threaded "thermometer" end of the switch disintegrated and instead of replacing it, i jb welded it into place. i saw a thread where Cliff Harris did that so i thought i would try it. the code does not return once the engine is warmed up, i suspect that when i epoxied it in place, i did not put it in far enough, or the jb weld provides a bit too much insulation on the thermometer end of the harness. I have ordered a new one and that should clear that code.

^^I provide this last bit of information if there is some link between the tcc early lockup and this egr is all.


Testing plan going forward:

- my suspicion is a shorted harness. my plan is to put a test light across pins and see if the light is always on.
problem with this theory is that the tc is not trying to lockup in 1st gear which i would think it would be trying to do if it was always on.

VikingTrad3r

As an anecdotal observation, I can say that it does seem that the 85 has a surprisingly high number of threads about early TC lockup. Chugging, Lugging, and just early lockup in general. With no outcomes or solved threads.

The only thing that seemed like a solution was on an earlier threads from back in 2002 i think, I read that BJankunski switched to a 1987 prom chip from a gto and it made his trans shift perfectly.

This sort of leads me to believe that the PROM chip for the 85 is simply set to lockup the tcc very very early and at very low rpm which causes the lugging.

I find this hard to believe that people would have paid for a corvette with this type of driving experience. So i have a hard time beleiving that its the prom chip.

WVZR-1

There were MEMCAL revisions for the TCC in '85!! 1227805 was the most recent that maybe included that. Here's a very old post with comments.

https://www.corvetteforum.com/forums...utomatics.html

Anyone that commented about using anything other than an '85 MEMCAL/CALPAK for correction needs to be asked questions as the '85 was a single year ECM and used a MEMCAL/CALPAK and the '86+ applications used a PROM that eliminated the use of MEMCAL/CALPAK individual components.

*** There were 2 CALPAK for '85 - An AT and also a MT, I've no idea what the incorrect CALPAK might have on driveability (it's been a very long time). Have you ever opened up your ECM to investigate which are in it? It might be a thing to do.

Here's a typical '870 type ECM with a MEMCAL (left) & CALPAK (right)

https://www.eecis.udel.edu/~davis/z2...m870memcal.jpg

DaveP85C4 had/has an '85 and would actually maybe know what driveabilty issues an incorrect "CALPAK" not "MEMCAL" might have on driveability.

bjankuski

This is a good test plan but an FYI is that the trans will never lock in first gear, because internally it is not possible for lock-up in first gear.

bjankuski

I just checked a stock 1985 chip and it will lock up the TC at 15 MPH and higher at more then 3.1% throttle, in 2nd and 3rd gear. It will unlock once you exceed a 23% to 99% throttle depending on the speed but that is why the car appears to be lugging. In my opinion the chip needs to be adjusted.

VikingTrad3r

between wvzr1 and bjanks post, and the evidence, i feel there is enough probability of suspecting the issue is the oem non-updated prom chip that i will firstly pull the ecm and compare my chip to the latest one. this would be an absolutely simple fix on a car that has been incredibly challenging for me to fix this far and im hoping the two of you are right on the money!!!


here is a link to the noted upgrade chip identified by wvzr1.

strangely in the ad it says that its from a 4+3 but then also says its from an automatic trans.

can anybody verify the same prom chip is used no matter which trans is in service?

http://www.ebay.ca/itm/85-CORVETTE-C...-/191401742717

WVZR-1

That I'd say ISN'T the newer that the TSB seems to mention. That is an older it seems but looks to be for an A4. You need to pull yours and if the ECM is original there's likely a decal/label on the ECM proper and then the information from the actual MEMCAL might be the "telling tale". Buy NOTHING without looking!

If my information matches the TSB and I haven't looked you would like to see 3200 HLH on the MEMCAL.

VikingTrad3r

As usual, you are bang on WVZR-1. Looks like the updated version is HLH3200

mine is HLH 2292 which is the late 85 chip. There was apparently an earlier model 85 chip as well. you can see them listed here: https://www.eecis.udel.edu/~davis/z28/

i use control F and then type HLH

VikingTrad3r

I think GM did in fact adjust the chip in the 85 quite later on, making an adjustment to have the tc lockup not until 41mph (a HHUUGGEE increase over the 15mph, what were they thinking???).

They appear to have had the early 85 chip, late 85 chip, and then this updated chip.

VikingTrad3r

i ordered the new chip.
I CANNOT WAIT

oldguy'sc4

I noticed that the HLH 2292 chip mentions 22lb injectors, and that the earlier version mentions 24lb injectors. Will the 2292 work with the 24lb injectors, or will there be problems?

VikingTrad3r

that is odd.

but i can verify that i have 24# injectors in my 85 with these markings:

0-280-150-223, and 5-235-041 (application: 1985 corvette 350, 24#)

ex-x-fire

Why not install one of these? It gets rid of the 2-3 lock up.

VikingTrad3r

thanks for that. i might! if this doesnt work.

WVZR-1

I don't know how much the KIT in the video sells for presently but it would seem that it could certainly be fabricated less expensively! I noticed that the solenoid was just "butt connected" to the harness and I believe I've seen similar offerings where the wires were "butt connected" closer to the pass through. A consideration for cruise function needs to be factored into the wiring on a "driven" car. I didn't study the switching and hydraulics but it might actually be better to be "left alone" in a driver with accessories!

It might be an interesting conversation to have with the vendor! I'd certainly be talking/questioning it's application before doing a buy!

VikingTrad3r

That. And, my 87 drives perfectly fine the way it is with the computer locking the tcc as long as its over 41mph i believe. im confident that this updated chip for the 85 (which essentially brings up to the minimum speed condition as my 87) will fix the annoying low speed lockup which causes lugging and some bad sounding exhaust if you have loud exhaust!

thanks again. looking forward to inserting the chip and firing it up.

IF THIS SOLVES the problem, I cannot believe that i have not seen a thread on it before devoted to the 85. there are a remarkable number of 85 owners generated threads complaining about early "shifting" they feel which is actually early lockup which they think is the car going into 3rd gear so early (15mph). Its actually the tc locking.

If it works, I'll write up a quick tech tip for 85 owners on the subject and use all the right words so future owners can find it.

Silver85

I am running myself ragged trying to find a post as to whether or not this worked. inquiring minds want to know!!!

Did you send your chip to be reflashed or did you download and do it yourself? I don't have a way to flash them but would invest in one if I need to. I would rather simply buy a chip because I really don't see myself doing any custom tuning.

VikingTrad3r

Hi silver, i can confirm it 100% solved it. After putting this chip in my 85's 700r4 began shifting exactly the same as my 87. the 85 has a substantially higher tc stall which is why it always felt faster (and it was, my bro and i dragged each other) they changed a few other parameters in the chip as well and it helped the idle too.


the issue, as i learned, was because gm had programmed the early and mid (even mid-late) year 85 ecm's to lock the tcc way way way to early and while it got the mpg numbers they wanted, as you mist be experiencing, it sucks! i cannot, i still cant, believe anybody would have taken delivery of thier 85 as it shifted like that.

I actually just wrote about this in somebody elses thread. I sold the 85 to a very happy new owner who is sort of parking it and storing it.

so if you have this issue, its all your chip.

i bought mine from a wrecker, his name was jason.

Silver85

Looks like $129 is the going rate on the auction site. Might see if I can scavenge one from a junk pile somewhere first.

Of course.....it won't do me any good until I get the interior put back together!