Pennock's Fiero Forum
  Technical Discussion & Questions
  Shift light stays on in deceleration, stumbe

Post New Topic  Post A Reply
Email This Page to Someone! | Printable Version


next newest topic | next oldest topic
Shift light stays on in deceleration, stumbe by PatrickTRoof
Started on: 03-18-2021 02:46 PM
Replies: 19 (328 views)
Last post by: PatrickTRoof on 04-05-2021 07:16 AM
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-18-2021 02:46 PM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
My 1985 GT 4 speed has developed an issue now where the shift indicator light will stay on even when I let off the gas. Normally, if the car reaches the right speed to trigger the shift light, and you let off the gas, the light will go out immediately. Now, it will stay on when decelerating between 3-2K. This is a sporadic problem, meaning it will do it sometimes and then stop. This issue is accompanied by a stumble at around 2.5K at low throttle input. I'm not sure if the stumble is from RPM or throttle position. I can't help but think the two issues are connected.

I just installed a brand new distributor less than a week ago, and the car ran great for a few days before starting in with this. I made sure the timing was set the right way. IAC is set correctly. I just did a sweep test of the TPS with a multimeter, and from what I could tell it looked good, though I've ordered a graphing meter to get a more accurate reading of it. When that arrives I'll test the MAP sensor too.

If anyone has any other ideas, I'm all ears, please!!!

[This message has been edited by PatrickTRoof (edited 03-18-2021).]

IP: Logged
PFF
System Bot
Patrick
Member
Posts: 31446
From: Vancouver, British Columbia, Canada
Registered: Apr 99


Feedback score: (1)
Leave feedback





Total ratings: 446
Rate this member

Report this Post03-18-2021 09:18 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by PatrickTRoof:

Normally, if the car reaches the right speed to trigger the shift light, and you let off the gas, the light will go out immediately. Now, it will stay on when decelerating between 3-2K. This is a sporadic problem, meaning it will do it sometimes and then stop. This issue is accompanied by a stumble at around 2.5K at low throttle input.


The shift light is something that a lot of us, after the novelty has (quickly) worn off, disconnect. I know I sure as heck didn't want a red light continually flashing and potentially distracting me from noticing when a real issue was occurring.

Having said that, it is rather odd that the shift light would sporadically stay on when the gas is let off.

[EDIT] Heh heh... I found an earlier post of mine regarding shift lights.

 
quote
Originally posted by Patrick Here:

As has already been suggested, the best thing to do in regards to the "SHIFT" light is to remove the bulb. In case you're not aware, the "SHIFT" light is to inform the driver of when to shift gears to help maintain the best fuel economy. Is that what anyone really wants, some incessant nanny telling you when to shift... over and over and over and over again?

I found it nothing more than a constant distraction. If a red light illuminates on my instrument panel, I want it to be indicating something important.



[This message has been edited by Patrick (edited 03-18-2021).]

IP: Logged
olejoedad
Member
Posts: 14641
From: Clarendon Twp., MI
Registered: May 2004


Feedback score: (5)
Leave feedback





Total ratings: 192
Rate this member

Report this Post03-18-2021 09:25 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
Shift light is controlled by ECU.

Do you have a spare ECU that you could install?
IP: Logged
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-19-2021 04:31 AM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
Patrick, I agree that the shift indicator light, while a cool feature, is a bit distracting, especially now in my case with its hyperactive behavior. However, right now, it seems to be indicating that I have a problem and I'd like to find it, haha!

Olejoedad, I believe I do have a spare or three kicking around. Do you happen to know if they're all the same except for the prom chips?

[This message has been edited by PatrickTRoof (edited 03-19-2021).]

IP: Logged
olejoedad
Member
Posts: 14641
From: Clarendon Twp., MI
Registered: May 2004


Feedback score: (5)
Leave feedback





Total ratings: 192
Rate this member

Report this Post03-19-2021 07:02 AM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
They are not all the same.
However, any V6 manual ecu will work as long as it has the prom that came with it.
I suspect the shift light programming is contained on the prom.

And any advice I share is worth exactly what you paid for it.

Ryan at Sinister is a good resource for you on this.....
IP: Logged
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-19-2021 08:48 AM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
I think the prom would tell the ecu whether it has a 4 or 5 speed, but I think the actual switching is done by the ecu. I'll have to do some research. I know the ecu uses engine speed and vehicle speed to tell what gear the car is in, then uses vacuum from the MAP sensor to determine when to light the indicator. I think it also uses tps input, which is why the light *normally* goes out when the throttle is closed.
IP: Logged
olejoedad
Member
Posts: 14641
From: Clarendon Twp., MI
Registered: May 2004


Feedback score: (5)
Leave feedback





Total ratings: 192
Rate this member

Report this Post03-19-2021 09:57 AM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
The ECU doesn't know if it's a 4 or 5 speed, it doesn't need to know.

The shift light is a manual only feature, most likely carried on the prom.

I have attached a photo that may help you.
IP: Logged
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-19-2021 01:00 PM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
It does need to know if it's a 4 or 5 speed. If you have a 4 speed and you accidentally put an ecu from a 5 speed in there, you're going to be riding around in 4th gear with the shift light on, because it thinks it has one more gear. Thanks for the photo though, that is helpful.
IP: Logged
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-20-2021 10:53 AM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
I fixed it. When I came out from work last night, the car started, ran for one second and then died, and I knew exactly what that meant because it happened one time before. Pin C of the 4 pin connector on the ICM had come loose. Pin C provides RPM reference signal to the ECU. I pulled the pin out of the connector and bent the tab out so it would fit tighter, and plugged it back in. The car fired right up, ran great with no stumbles, and the shift indicator light worked exactly as it should.

Say what you want about the little orange arrow, but in this case it did a good job of telling me something was wrong! LOL

Thanks everyone for the replies.
IP: Logged
reinhart
Member
Posts: 540
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-22-2021 06:21 PM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
Looking at that ECM PROM chart, are the Federal and California PROMs actually different as far as programming? My understanding was Ca vs Fed cars were all the same. GM just wanted to charge extra for CA cars.
IP: Logged
olejoedad
Member
Posts: 14641
From: Clarendon Twp., MI
Registered: May 2004


Feedback score: (5)
Leave feedback





Total ratings: 192
Rate this member

Report this Post03-22-2021 07:55 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
Patrick, there is no feedback from the drivetrain to the ECU relative to what gear a manual transmission is in.
None at all.
IP: Logged
PFF
System Bot
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-23-2021 02:24 PM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by olejoedad:

Patrick, there is no feedback from the drivetrain to the ECU relative to what gear a manual transmission is in.
None at all.



I realize this. But like you said, it's in the chip.
IP: Logged
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-25-2021 05:04 PM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
Update: The issue kept returning, no matter how I fiddled with the connector. I think the connector got messed up from changing the ICM a whole bunch of times thanks to the distributor making me think the ICM was bad (see my other post: //www.fiero.nl/forum/Forum2/HTML/144767.html ). This was annoying, as I had only recently replaced the original connector with a replacement.

Luckily I had ordered an extra connector a while ago. I cut out the other one, spliced this one in, and haven't had the issue since (knocks on wood, kisses the rabbit's foot and throws salt over the shoulder).
IP: Logged
Dennis LaGrua
Member
Posts: 14031
From: Hillsborough, NJ U.S.A.
Registered: May 2000


Feedback score:    (13)
Leave feedback





Total ratings: 323
Rate this member

Report this Post03-26-2021 03:14 PM Click Here to See the Profile for Dennis LaGruaClick Here to Email Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by olejoedad:

Patrick, there is no feedback from the drivetrain to the ECU relative to what gear a manual transmission is in.
None at all.


Absolutely, I believe the ECM uses a comparison between speed and RPM's to energize the shift light. In view of this there may be different prom chips that define those speed v RPM points relative to the FDR's. Last I looked the shift light can be turned on and off by unchecking the feature flag in the program.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

IP: Logged
olejoedad
Member
Posts: 14641
From: Clarendon Twp., MI
Registered: May 2004


Feedback score: (5)
Leave feedback





Total ratings: 192
Rate this member

Report this Post03-28-2021 06:19 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
Shift light actuation is most likely due to MAP sensor vacuum signal.
I'm on vacation and away from my factory service manuals, so that is conjecture at this point.
There is probably and answer in the Drivability section.
IP: Logged
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post03-30-2021 05:21 PM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
No worries, I fixed it by replacing the 4-pin connector to the ICM.
IP: Logged
olejoedad
Member
Posts: 14641
From: Clarendon Twp., MI
Registered: May 2004


Feedback score: (5)
Leave feedback





Total ratings: 192
Rate this member

Report this Post03-30-2021 05:34 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
Good deal Patrick
IP: Logged
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post04-02-2021 07:40 PM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
Welp, I thought I fixed it. I drove the car to work today, and it started in with it again. I got to work, unplugged the 4 pin connector, plugged it back in and drove it, no problem.

On my break I went for a drive. It was fine for a few minutes, then started acting up again. I'm out of ideas.
IP: Logged
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post04-03-2021 10:27 PM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
This is going to be one of those gremlin issues that comes and goes, driving me crazy. I'm leaning toward the TPS now.
IP: Logged
PatrickTRoof
Member
Posts: 597
From: Baltimore, MD, USA
Registered: May 2013


Feedback score: N/A
Leave feedback

Rate this member

Report this Post04-05-2021 07:16 AM Click Here to See the Profile for PatrickTRoofClick Here to Email PatrickTRoofSend a Private Message to PatrickTRoofEdit/Delete MessageReply w/QuoteDirect Link to This Post
I replaced the TPS. I don't want to jinx myself, but yeah.....
IP: Logged

next newest topic | next oldest topic

All times are ET (US)

Post New Topic  Post A Reply
Hop to:

Contact Us | Back To Main Page

Advertizing on PFF | Fiero Parts Vendors
PFF Merchandise | Fiero Gallery | Ogre's Cave
Real-Time Chat | Fiero Related Auctions on eBay



Copyright (c) 1999, C. Pennock