Speedometer issues at idle - other electrical oddities

[pjkinsella]

Hey guys, new guy here.

I just acquired a 98 Viper GTS (King Snake) that's had a ton of work done to it over the years, so I know this may be a difficult one to answer definitively, but I'm just looking for some ideas of things to look for.

Weird things that are happening:
- Speedometer is fluctuating around 40 mph at idle (and yes that means odometer is ticking up!). When the car is moving, it seems to be working fine.
- The left turn signal (dash light) is faintly lit.
- After the car heated up, the shift light came on and stayed on (aftermarket, obviously).
- The oil light came on.
- The car will not idle until it's warmed up (this may or may not be related).

This has an aftermarket AEM ECU, but also still has the factory computer. That means there's extra wiring everywhere, so I have a lot to sort through. This car has been sitting for a while, but when I bought it a week ago, everything seemed to be normal.

My initial thought was that it's a low power, or high amp draw, issue (if you've been in a car that almost completely loses electrical power, everything just goes haywire). But it could also be a wire that rattled loose, or was mostly chewed in half by a mouse.

A ton of variables, I know, but if anyone has any experience with something like this and might have a few pointers on where to start, I'd really appreciate it!

[Blue96GTS]

Battery issues definitely cause weird problems with these cars, IMHO. I'd start with a good battery first, then see what is left to address.

Good luck and congratulations!

[flyingskibiker]

Pretty generic answer, but bad grounds cause havoc...

[pjkinsella]

Yes, on both accounts. I will be checking on those initially. Currently the battery is reading about 12.4v, which is a little low but doesn't seem low enough. I know I have one ground wire hanging on by two strands. I need to fix that ASAP. Could it be that simple?? Something tells me no, but that's just the pessimist in me, ha.

[Steve-Indy]

I am going to switch to this thread from the other site as it is easier to use on my smart phone

At idle, I suspect your alternator is doing little for you battery... which I am betting is older than new. One also wonders if, by chance, you have an inderdrive pulley which will make matters even worse.

[pjkinsella]

Yeah, I'll report back when I actually have a chance to dig into it a bit. Any idea what size the crank pulley should be, stock?

[AZTVR]

Yeah, I'll report back when I actually have a chance to dig into it a bit. Any idea what size the crank pulley should be, stock?

See photo in first post: http://driveviper.com/forums/threads...erdrive-Pulley An underdrive pulley is probably going to be aluminum "color."

[pjkinsella]

See photo in first post: http://driveviper.com/forums/threads...erdrive-Pulley An underdrive pulley is probably going to be aluminum "color."

Ah, okay, that's a huge difference. I believe it's stock then. Thank you!

[Steve-Indy]

"Feeds and Grounds" !!! I wonder if you have a little of both types of issues. Funny stuff at idle can still be post-startup battery state, couples with relatively low alternator output at idle. Of course, if you have driven it to warm it up, you have likely begun to restore battery charge and it will run better, and Speedo (often tach as well) will settle down.

Grounds can be a bear to track...but necessary...especially if you have turn signal issues. Sometimes spooky things happen due to micro corrosion (or macro corrosion due to flooding!!) due to damp environment which can affect switched, fuse and relay sockets, etc.

Cobbled up/poorly done wiring is another problem...suspect shift light, AEM, stereo upgrades, etc. Hell, one can even see some weird stuff after removing console for harness installation. These are only a few things that I have seen over 20 Viper-years...and, I am just a hobbyist.

Are you sure you don't want to inspect/access/date battery directly first??

[Dan Cragin]

Does his car have a speedometer recalibrator?

Dan

[steve911]

Does he car have a speedometer recalibrator?

Dan

Dan you took the words right out of my mouth!

[pjkinsella]

Does he car have a speedometer recalibrator?

Dan

Dan, I honestly don't know. I was wondering that myself. What's the easiest way to determine whether I do or not?

[Steve-Indy]

Dan's question implies non-stock diff...so, put in 6th gear at 70 mph to see if RPM is around 1350. If much higher, you have non stock diff, and more likely to have "speedo recalibrator".

[pjkinsella]

Dan's question implies non-stock diff...so, put in 6th gear at 70 mph to see if RPM is around 1350. If much higher, you have non stock diff, and more likely to have "speedo recalibrator".

I can tell you that it's at right about 2,000 rpm in 5th gear at 55mph, if someone can calculate that, haha. The only reason I know is because I was in a 55 zone, and the rpm's were pretty much too low in 6th, and at 2,000 rpm, the exhaust is SUPER droney (is that a word?). At 55 in 6th, it was jerky (lumpy cam, close to a high idle).

[BrianACR]

I can tell you that it's at right about 2,000 rpm in 5th gear at 55mph, if someone can calculate that, haha. The only reason I know is because I was in a 55 zone, and the rpm's were pretty much too low in 6th, and at 2,000 rpm, the exhaust is SUPER droney (is that a word?). At 55 in 6th, it was jerky (lumpy cam, close to a high idle).

I know in my car 50mph in 6th is pretty much bang on 1000RPM. Completely stock everything. At 75mph on the highway its 1500. Not sure if that helps at all.

[Steve-Indy]

OK... Stock 01 which has stock wheels (18") and tires:

55 mph in 5th gear...about 1725 RPM.

Will try a couple of others shortly and update post.

99 ACR, stock...18" stock(for ACR) BBS wheels: 55 mph is just under 1700 RPM in 5th gear.

96 R/T 10 stock with OEM wheels (17") and tires: 55 mph is just under 1700 RPM in 5th gear.

[pjkinsella]

Yeah, based on what you guys are saying, I must have stock gearing. I'd think my rpms would be quite a bit different if it were altered gearing.

[Steve-Indy]

Yes, I agree. 3.55 or 3.73 were often installed with upgrades. In fact, one now defunct "tuner" seemed to rely of this switch to give customer the feel of HP gain...be it real or perceived.

[pjkinsella]

I noticed last night that it does have a sticker under the rear end for an aftermarket differential company. Can't remember the name. I'll have to dig into it further.

Also, I tried to start the car and it only clicked. Apparently the 12.4v wasn't enough to crank! I'm going to fully charge the battery and see if the gremlins are still there. If they go away, I can be pretty sure that it's a voltage issue (either old/dead battery and/or slacking alternator). Will report back!

[pjkinsella]

Well, I got the battery all charged up nicely, went to start the car, and just hear the starter click. Excellent. Surely I have a bad connection somewhere.

I then hooked up my (small) charger to the front posts and put it in engine start mode. Tried cranking and it gave it enough juice to actually turn over for a half second. I could be wrong, but this tells me that maybe the full amperage of the battery isn't making it to the starter. It's just enough to run the fuel pump, gauges, and solenoid, but won't crank. I'm thinking I need to attempt to jump the terminals on the starter to rule out the ignition wire, and then pull the wheel and check the connections on the battery.

Any other things I should check in the process?

[Steve-Indy]

Check connections at starter...common to corrode and/or loosen over time. I would also check battery cables at connectors to battery...common to corrode due to out gassing around terminals. Be prepared to clean and "recondition" battery tray at the same time.

[daveg]

Unless the battery is new, replace it, mine did the same thing after charging overnight, probably dead cell.
I would never use start mode from a Battery Charger, could fry computer.

[pjkinsella]

Unless the battery is new, replace it, mine did the same thing after charging overnight, probably dead cell.
I would never use start mode from a Battery Charger, could fry computer.

This has an optima battery, and I'm very disinclined to believe it is the battery at this point. Throwing money at a problem has historically been more painful than helpful to me over the years!

As for frying the computer, can you explain why, or is that just something you've heard?

[daveg]

This has an optima battery, and I'm very disinclined to believe it is the battery at this point.

So was I until I replaced it. Check date code on battery.

As for frying the computer, can you explain why, or is that just something you've heard?

Read a few times, never had it happen to me because I don't do it. I always use a trickle charger to charge battery.

[Steve-Indy]

daveg, I know of nearly a dozen instances of presumed damage to Gen II Viper PCM's that were observed to occur when operator hit button for a starting boost of 50-200 amps. I also know that this happened to an engineer's 97 Dakota truck. Said PCM's were fine until the extra amps. While I have started MANY Vipers with dead batteries with car to car method, booster packs, and free standing batteries, I always avoid those extra amp temptations.

It is MY supposition that the Gen II jumper posts are just above and below the PCM. That, coupled with a very low and/or internally shorted battery may change the battery's ability to buffer a surge. Believe me, I have beat this to death at AM coffee in the presence of electrical engineers. Who knows for sure??!!!


I am fairly certain that there are folks who have gotten away with this maneuver, but I am unwilling to take that risk. And, yes, I have failed to start a few Vipers with jumping, and, therefore I have replaced both Gen I and Gen II batteries in some unusually tight places...which is ne fun !!