sounds like stop and go driving to me. On a serious note, a more descriptive description would help along with the year, make model and if it's auto or manual gearbox type stuff could go far in helping provide useful input. ciao chris
For starters I'd reseat (multiple times) connectors L17 and G151 and use a terminal stabilizer. If you loosen the air mass meter main clamp, unclip the connector, and take off air clean cover you'll have just enough space to reach in there, just above and a little behind the backup light switch. The big round G151 connector is under the plastic tray at the rear of the engine bay. The actual terminals there for speed pulse are #14 & #18, those wires lead to the speedo, terminals C3 and C4 (top left connector of speedo head). I'm assuming you have a 164 L, B or S.
We all need stabilizing! It's what Del calls dielectric grease. I use Stabilant 22, described thus...
Stabilant 22 is an electrically active material which stays resident within a contact-pair, there enhancing conductivity without causing electrical leakage between adjacent contacts. Although Stabilant 22 does have a detergent action it is not sold as a cleaner, just as it has a good lubricant action but is not sold as a lubricant. Stabilant 22 is used to increase the reliability of contacts. Tenfold to one hundred-fold increases are not unusual. At the present time it is used in many different types of contacts, including card-edge connectors, D-type connectors, MIL-spec connectors, signal switches, etc.
Stabilant 22 is an initially non-conductive amorphous-semiconductive polyoxyethylene-polyoxypropyline block polymer with a molecular weight of about 2800 that, when used in thin films between contacts, acts under the influence of the electrical field and switches to a conductive state. The electric field gradient at which this occurs is established during manufacture so that the material will remain normally non-conductive. Its switching speed is too slow to allow it to be used in the more traditional semiconductor applications; however, this means that signals at frequencies substantially above five cycles per hour will not be modulated by the switching characteristics of Stabilant 22.
Thus, when applied to electromechanical contacts, Stabilant 22 provides the wide-bandpass connection reliability of a soldered joint without bonding the contacting surfaces together!
Another possibility for erratic speedo is something I think you yourself reported: cracked insulation where the wires come out of the L17 sender, and moisture entering.
I used Stabiliant on a number of electrical connectors on my cars. Its hard to prove a negative, but since I haven't had any issues with connectivity on those connections since usage, I think that its working??
VW and Audi thought it was a good enough product that they gave it an internal part number, and recommended usage in technical bulletins.
Its completely different from Dielectric grease. Dielectric grease is not conductive. Its an insulator. Its great at keeping out moisture in wet-prone connection areas, though, that would then lead to corrosion of the connections. It doesn't do anything to enhance an electrical connection.
My rule of thumb is if it gets wet and dirty and has moderate or high load, go with the grease. Generally dry and lower/more sensitive connectors, go with the enhancer. For whatever reason, I'm under the impression that the enhancer is also not to be used for O2 sensors...
Here's a good quick summary of the contact enhancers that I ran across a number of years ago:
Then again, it could be the actual gauge. This is basically a small motor with a thin shaft and pointer needle attached. If the motor is collapsing, will be erratic or stop all together. Taking it out is a hassle so check all other possibilities first so you don't go digging into the dash unnecessarily. Did you specify the year and model? Different years use different size motors, pointer needles, etc.
That's certainly possible. My speedo was acting up the last weeks of the summer, suddenly cutting out for a few seconds then coming back, then longer periods of cutting out, like 5 minutes. The reseating of those two connectors and treatment of Stabilant 22 has, cross the fingers, has had positive results for two weeks in a row, so like Andy I have to say, "I think it's working". Having a speedo cut out on an "S" (or QV) will make the CDS suspension default to rigid because the CDS ecu thinks the speed of the car is zero, or standing still. On another discussion group, also about speedo problems, I read the sentence, "are you getting all your pulses?", which suggests to me that the "S", besides the possibility of loosing your speedo completely, may also be subject to loosing the CDS if the "quality" of the pulse is not good. Thus the sine wave may be good enough to get a speedometer reading, but if the quality is not perfect, the amplifier in the "S" speedometer that sends the signal to the CDS ecu may not cut mustard. By the way the cruise control ecu shares the same amplified signal. Any comments on this theory of "quality" of the sine wave?
I have tested GTV6 speedometers on the bench and I found that the voltage of the pulse must be over 50% of the voltage supplied to the speedometer. If you have a weak pulse and the speedometer is not working then you turn on the fan and the windshield wipers then the speedometer might start working. The solution is to make sure that you have a good 12 volt supply and a good ground to the sender unit.
There is a good chance that 164 speedometers are similar.
This may not be exactly what amintaghavi is seeing, but my speedometer does this awesome bounce dance party when it's especially cold out, until the engine gets up to temp. My assumption is a bad connection at the speed sensor that gets better as the ambient temp in the engine bay gets high enough.
I think your analysis is correct. That's a pretty dirty area around the L17 connector and although the connector has a built-in seal, after 20 years+ all things electrical begin to get dodgy. My speedo stuttering could be like yours but also be intermittently dead. You may not have noticed it but during these panic attacks the suspension will default to rigid if you have the selection on "auto".
In post #3 I supplied a diagram of the G151 connector from Alfa's handly wiring charts. I was doing some checking today and discovered that there is something fundamentally wrong with the picture! The male and female halves on the top of the chart should be reversed, then it makes sense. The bottom half of the chart is okay.
Perhaps Steve Alfisto or someone else has already remarked on this.
"Dielectric grease is not conductive. Its an insulator. Its great at keeping out moisture in wet-prone connection areas, though, that would then lead to corrosion of the connections. It doesn't do anything to enhance an electrical connection"
That's exactly what I use it for. Living in an area where there can be a lot of rain during parts of the year, dirty water gets everywhere in the engine bay, and if a connection is not protected from that, contact can be sketchy at best. I clean the connection with electronics spray, etc, and then coat everything with the grease prior to reassembly.
Was it ever made clear he model and year or did I just miss it? If it is a pre-94-95 change model then I have a spare speedo and tach looking for a new home. I cannot test as they were taken from a spare cluster I cannibalized for a metric-mph gauge face but they are yours as long as you pay for the postage. You may be able to apply voltage to the leads and test but I am not sure.
P.M. me if interested. You can also have the odometer.