Green93

I guess it's time for the next chapter of my love/hate relationship with the truck in my signature. I cleaned up the garage today so I can pull her in tomorrow after work and take a look. Just wanting to get some advice before I start.

Awhile back I had intermittent issues with the tach. Driving down the road it would just drop to zero. At other times it would bounce up and down as I sat at a stop light. That issue seems to have switched to the speedo now. It will drive fine and out of nowhere it will jump randomly. The biggest problem is that ill be driving about 50km/hr and it will read 140km/hr or more. At that point it's like I'm in neutral. I can rev the truck but nothing happens. I then coast off to the side and wait for the issue to subside. No rhyme or reason as to when this happens.

I have the FSM and starting to read through it. I'm just over my head with electrical and auto tranny issues. Any help with where to start and what to check would be great, I need this truck up and running dependably. My thoughts are its electrical and not mechanical. Is the speedo causing the issue? Or is the tranny?

Halp, Jason.

Green 88

My guess on the tach issue would be a poor connection behind the cluster on the flexible circuit board where the plug attaches.
I think your speedometer is mechanical (plastic gear, cable, to the speedo head). If it's an electronic speedometer then I would look at the same plug mentioned above that's behind the cluster.

Co_94_PU

iTrader: (-1)

92 Models coud be electric or mech, depends on the factory and manufacture date(91?).

Assuming it's electric make sure all your grounds are clean and firm.
There are two VSS on the electric, one for the ECU and one for the gauge. Both malfunctioning at the same time leads me to grounding problems.

That has the Electrical controlled transmission, IIRC, are you running around in sport mode? (ECT lighted on the indicator panel, if the bulbs not blown) If so try the other mode and see if it helps any.

That sounds mechanical or at best electro-mechanical.

Does the throttle have any effect on the gauges when this is happening, eg the shaft(s) spin but the diff' is not connecting.

Check ALL your fluids.

Green93

Hey guys, thanks for the insight so far. The truck is a 93 and electric VSS. I do use ECT for spirited drives but have not been using it anytime this happens. There is no clunking or anything, it just seems like it's in neutral. This only happens once the speedo shows considerably faster than actual speed for a few seconds. If the speedo jumps and moves right back to actual speed there is no effect on the transmission. I just got home from work and as soon as the wife gets the truck back (crosses fingers) I'll check for codes and look at the easy stuff first.

Green93

Well I made a little progress tonight. Checked for codes and came back with a code 42. #1VSS. I unhooked the battery and pulled the dash apart. Last summer I swapped to an SR5 cluster. I tested it as per the FSM and the VSS was ok. I decided tonight to reinstall the original cluster just to isolate the problem. Took it for a drive and everything is ok so far, although he problem is intermittent. Checked codes again and all clear. Crossing my fingers that I just have to replace the VSS in the SR5 cluster and reinstall.

Co_94_PU

iTrader: (-1)

Let me clarify for you VSS#1 is the Vehicle Speed Sensor, it is mounted to the transmission not a part of the cluster. The cluster does not send any sensor data to the ECM.

second page of the "Electrical Control System" section , AT-64 not 100% sure which transmission you have but the diagnostic system is similar.

I'm going to assume you got the diag code 42 from the MIL/CEL, not the transmission (OD Off, light). The ECT diagnostics are here

The transmission type is listed on the door panel, second half of the ATM section. it should be an A340 E A or F. The index has sections for each letter type.

Green93

I think I finally have a handle on this. I got off on the wrong foot and ended up doing a bunch of extra work. First step should have been to clarify which tranny I actually have.

I have an A340H. The trouble codes I have been getting are from the O/D light. Not the check engine light. I ended up on page AT-178 for the A340F. There it states code 42 is faulty #1 speed sensor in the combination meter.

You were correct, for the A340H the #1 speed sensor is located just before the drive shaft. Live and learn.

The wreckers didn't have a sensor so looks like ill be combing Craigslist with my fingers crossed. Tomorrow ill be swapping clusters and maybe cleaning out the blower and vents before reinstalling. Also checking wiring from the #1 VSS to the ECM.