Bogus tach/RPM jump with MAP increase (poltergeist?)

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te51levin
Helpful MS/Extra'er
Posts: 72
Joined: Wed Mar 22, 2006 8:35 pm
Location: PNW

Bogus tach/RPM jump with MAP increase (poltergeist?)

Post by te51levin »

Vehicle: 1985 Toyota MR2, VAST ignition, stock ignitor
MS: MSnS-E on V3 board running both fuel and ignition

The car's been running fairly well on MSnS-E for a couple of months now. I had been tweaking the fuel map slowly here and there, but I recently got a chance to ride shotgun and mess with the fuel map while a friend drove the car. After we drove around for a couple of hours, something very strange started happening: at engine speeds below 2100 RPM, opening the throttle now causes the tach needle to jump to roughly twice actual RPM. Releasing the throttle returns the needle immediately to actual RPM. This happens on both the car's tach and on the MegaTune display. The engine also bogs during this event, so I wonder if the injectors are not opening twice as long. I haven't had anyone else drive the car so I could watch PW since I noticed the bog.

Other than changing fuel table values, the only other thing we messed with during the tuning session was the accelerator pump settings. I've tried playing with them but the problem remains.

At first I thought this was TPS related, since it happens when the throttle is opened, but lately I have witnessed the tachometer doing its little dance with the throttle fully closed (typically after a cold start). This seems to identify the stimulus as an increase in MAP (to anything above 65-70 Kpa). While driving, the throttle must be opened very slowly to avoid the problem. Anything after about 2100 RPM seems totally unaffected, and the car runs great beyond that point, but standing starts and heavy traffic are tricky. Cold starts and cold driveability are miserable.

My next step is to make sure there is no flux on the board and no moisture in the case, but I wanted to post and see if anyone else has encountered a similar problem.
'85 AW11 7A-GE daily - MSnS-E, v3.0
'77 TE51 2T-G dormant
te51levin
Helpful MS/Extra'er
Posts: 72
Joined: Wed Mar 22, 2006 8:35 pm
Location: PNW

Post by te51levin »

I just spent the evening rewiring the jumper cable from the DB29 to the car's wiring harness (it's plug-and-play) in case there were any internal shorts or problems. There's no change. There was no moisture or anything funny-looking isnisde the case or on the board, either.

Nobody else has seen anything like this before? Would it be of any use to update to a newer version of MSnS-E or reflash anything...?
'85 AW11 7A-GE daily - MSnS-E, v3.0
'77 TE51 2T-G dormant
te51levin
Helpful MS/Extra'er
Posts: 72
Joined: Wed Mar 22, 2006 8:35 pm
Location: PNW

Post by te51levin »

Reflashed the s19 file and all is well again.
'85 AW11 7A-GE daily - MSnS-E, v3.0
'77 TE51 2T-G dormant
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