stealth

I am pretty sure this has been discussed, but I'm not sure how to put a reasonable search in to find such discussion since all keywords involved are quite common.

What is the difference (other than the plug form factor and contact count) between the 94-95 idle/WOT switch and the early one? The WSM only gives calibration and diagnostic instructions for the 3-pin. Are the additional connections used by the 928 LH or did Bosch simply come out with a new part?

My frankenshark 90 GT has a 95 engine and a corresponding late TPS. Should I care whether someone took the GT harness and connected 3 compatible pins to a 95 connector, simply meeting the requirements of the TPS that would've been there on a 90, versus actually swapping a 95 harness in? The TPS has tested good for idle and WOT but wondering whether any engine behavior is impacted by the presumably-additional information on the other connections.

SeanR

If the TPS is bad on the idle contact, you will have fluctuations in idle. If you don't have the WOT connection you can't tell unless you have the hammer on it.

On that note, I was not aware that the 94-95 connector was different that the '85+.

stealth

Well, this car has had idle problems for a long time (one reason for intake refresh in progress..."had" may be "still has" but intake not reinstalled yet), but the idle and WOT signals have always tested ok with Hammer, so really aren't suspect. Just wondering whether I should care how a 95 switch plug ended up on it-- 6-pin (only 5 "live")-- could have been that the plug was spliced to 3 wires to match 90 LH expectations at time of engine install, or could be that the harness was also replaced (records are indeterminate about harness), and does any year LH chip care about these extra pins such that they would impact any aspect of the performance (mileage, idle, mixture). My WSM doesn't mention a 6-pin connector (or LH diagnosis for GTS, just S4/GT), so I don't know whether the additional pins and any signals they might carry matter to the LH.

The 94-95 part # ends in .01 versus .00 and has a 6-pin connector instead of 3-pin based on what I found on my throttle.

worf928

It doesn't matter for a 5-speed. There are actually only 4 live wires. The 5th lead is actually tied back to pin 3 which is a ground. The single extra wire goes to the kickdown relay on auto 94s and 95s.

Assuming that your original 3-pin harness hasn't been messed-up, I'd think you could just use a 3-pin switch from an S4/GT.

GregBBRD

Absolutely correct.

This requires removing the intake, however. It might be easier just to logic this out and figure out which signal needs to arrive at which pin, at the brains. I'm not at work, but this is easy, with a wiring diagram.

If there are idle and full throttle signals at the existing switch, it would be easy to get those signals to the proper pin postiions at the brains. This only requires an ohm meter and some basic wiring work.

If the signals are not present at the existing switch, then the switch needs to be replaced anyway and then you might as well use the 3 pin switch.

stealth

Either the harness was replaced with a GTS harness or it was less trouble to splice up the larger connector than to replace the switch when the engine was installed, because the harness has the large connector. Good to know that it matters not to the LH.

Sean, a prior owner spun a rod bearing (surprise, he did spend some time on the track) with the original engine, and procured a GTS engine from 928 Intl as a replacement, in 2000 or 2001.

stealth

The intake's already off, and Dave's Hammer has always indicated WOT and idle signals ok...but both his and another indicated knock sensor not present faults, which motivated the intake refresh. The rubber was all pretty good so it may yet turn out to be that idle problems are LH-related (even though the LH was replaced with new within the past 9 years, not 19).

If I were to use a 3-pin switch, I'd have to redo the harness to have the 3-pin connector.

PorKen

The 6-pin TPS has a potentiometer output as well as the regular idle and WOT switches. Automatic GTSs have a dynamic kickdown feature which uses the variable resistance output to kickdown if you move the pedal suddenly.


The S4-up (928 part#) throttle switch's rotation is opposite that of the S3 unit (944 part#).


The 951 TPS has a potentionmeter for the KLR (knock box) - this TPS could be used to install the dynamic kickdown relay on 85-86...

worf928

I am totally confused. In your first post, it reads to me like you describe a connection to the idle/WOT switch that's been cobbled together from a 3-pin harness to a 6-pin connection.

If you have a 6-pin switch and a 6-pin connector then, it would seem that the GTS harness and ECUs came with engine. Unless you see bits of electrical tape wrapping the 6-pin harness connection?

stealth

No tape (it's not impossible to recrimp the connector rather than splice, sorry, it was late and I shouldve said crimp since if a splice was done, it's well-hidden). Also, all the FI connectors are the new style (except one, which means whoever did the job would've spliced, not crimped, if they'd replaced the TPS connector, since they were sloppy with the connector on cyl 1's injector plug), so I now conclude it's a GTS harness.

worf928

Yup.

GregBBRD

Very confusing. Indeed, the first post was a question that seemed to indicate that the loom had a 3 pin connector.

Hook up the switch and see if you have the proper signals at the brains.

stealth

Just to add this info to the thread, since WSM doesn't show the calibration for the late auto TPS...this is what I reverse-engineered on the .01 TPS:

Pin 1 - 2: dynamic kickdown potentiometer
Pin 3: n/c
Pin 4: ground
Pin 5: WOT
Pin 6: Idle

The idle connection's really tight and I can't get that set properly without making WOT kick in at about 80%+ throttle (I believe ideal is to have the WOT signal at a lower throttle open % than that). I'm erring on the side of making sure the idle signal is good, hopefully that won't cause lean between 70-80% throttle.

worf928

You are correct that you need the idle switch to work. Period.

I have never seen an 87+ WOT/idle switch that will trigger WOT with less than 85-90% pedal travel.

stealth

I thought I had seen 3/4 throttle somewhere, or 2/3 (since I couldn't find it again, I don't remember which). Good to know my experience is in the range of your (much more extensive) experience, thanks!