TPS and possible ground issue

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toyotaspeed90
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TPS and possible ground issue

Post by toyotaspeed90 »

Not my first MS (first one was an old Glens Garage MS1 V2.2 in an 87 MR2 with a 4agze) built in ~2004. Personally built a 2nd MR2 with a MS1 V3 board (DIY Autotune). Completed several other installs on other MR2's.

Current vehicle (and issue) is a 1970 Land Cruiser with a 350 that I'm going fuel only TBI. Should be simple. Vehicle will start and idle. Was built using the megamanual instructions. No datalog to post and nothing has been changed to the MSQ other than loading the firmware in then changing constants for injectors/8 cylinders.

TPS won't read. In fact, calibrating the TPS causes a problem that I've researched and nobody else has mentioned. I went through the TPS check in the MS2 V3 megamanual and everything sort of checks out.....

The capacitors seem to be in place correctly (but can't read the writing on them, so can't 100% verify.... but I'm pretty good at following the install instructions for them).

The value of R9 seems accurate. There is a slight issue - that when checking between pin 26 and R9 the resistance values are backwards on the legs compared to the instructions in the megamanual..... which doesn't make much sense to me since resistors aren't directional?

The issue when trying to calibrate - is that the values will slowly rise on their own (so when nothing is happening other than 'key on' and click "get current" continually the values rise. The *same* thing happens if the TPS is completely unplugged. Tried to swap the 5v ref and signal and same thing happened. I have 2 TPS sensors and both are doing the same thing. I've verified the wiring at the DB37 multiple times. It seems to work on my old stim.


The 2nd issue is surrounding grounds at pin 7. I'm on my 2nd DB37 connector on the harness end.... this is because the first harness was built with stiff 14ga marine tinned wire - which seemed to go fine, except it made the harness difficult to maneuver. In any event, I ordered a new DB37 connector and the 20ga wire kit (23")....

So - the grounding issue seems to have happened on BOTH harnesses.... but the 2nd time it seems to be something else. I get continuity on the board itself between the "ground" (by the Proto area) and pins 1, 2, 7, 8 (etc) at the DB37. I get continuity between the sensors ground/return and the harness end of the DB37. Once I plug the DB37 into the MS1.... I don't get values for the coolant temp sensor nor the air temp sensor. On the original DB37 I had jumpered 7 and 8 and everything worked fine... it seems for some reason it's happening again - if I ground out the wire at the harness end I get coolant and air temp values.

The difference between the original DB37 plug and this one... is that the fuel pump wouldn't kick on until I jumpered pins 7 and 8.... now the pump works perfectly fine, but no readings for coolant/air temp sensors.

Thoughts?
billr
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Re: TPS and possible ground issue

Post by billr »

First thought: Quit using the Megamanual, it hasn't been kept current. Use the manuals linked-to at the top of this page.
toyotaspeed90
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Re: TPS and possible ground issue

Post by toyotaspeed90 »

I'll take a look - however I believe the firmware I used isn't different than the old firmware used..... it's a simple fuel only MS1 V3 board.

The grounding issue was resolved - there was a poor solder (my fault) on the DB37 to the board, of course at pin 7. Ran the iron (and solder, if needed) across it and most of the other major components on the board. I was able to diagnose it by checking for continuity between the return and the "Ground" on the board - not getting continuity, but getting resistance. Then checking continuity on the board, again... and the placement of the probe on the pin determined whether there was continuity. That is resolved.

The new harness was installed by individual male/female connectors (best way I could determine to connect 20ga wire to 14ga wire for optimal connectivity and protection - which is use a 18-22ga connection on the DB37 side and a 12-16ga connection on the harness side) both for ease and for diagnostic purposes.

TPS issue continues, even when the TPS is unplugged either at the TPS itself, or at the individual connectors (both 5v ref and signal disconnected from the harness).

Acting as if there's a capacitor increasing storage of energy and that's what's being returned to pin 26..... but really, at a bit of a loss on this one.


(I should note, in case it matters, I did use the instructions to use I believe pin 6 as a ground for ignition to reduce noise..... ignition is run with the coil signal and ground on shielded wire separate from the other 'new' wires).

Not using a relay board.
toyotaspeed90
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Re: TPS and possible ground issue

Post by toyotaspeed90 »

Looking at the Quick Links - that is the set of instructions I used for building the V3 board I have.... and for modifying it for fuel only.

Megamanual is what came about when researching TPS related problems.
billr
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Re: TPS and possible ground issue

Post by billr »

What is the resistance from the DB37 pin 22 and the 40-pin socket, pin 26? It seems that ADC input is floating, those little caps (C8&9) are irrelevant to that.
toyotaspeed90
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Re: TPS and possible ground issue

Post by toyotaspeed90 »

Set at 2K, measures at 0.981

Going to resolder the joints under the map sensor while I'm at it...
toyotaspeed90
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Re: TPS and possible ground issue

Post by toyotaspeed90 »

Problem fixed.

In my defense, my good adjustable iron had a bad heating element that I couldn't quickly get fixed, so I bought a cheapo Radio Shack iron... which is much larger.... so guess I should have gotten a quality iron in the first place.
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