Mark D chip & stomp test

[Sagaris]

My 1991 M20 has a Mark D chip. I have successfully performed a stomp test prior to installing the chip but I am not able to perform it after installing the chip. It is a chip for a 173 ECU and I am running it in a 524 ECU. I have the newer style TPS so adjusting the throttle position switches is out of the question. I even removed the intake boot and manually and watched the throttle open completely as I was trying to coax the car into coughing up some information.


Do performance chips cause you to lose the on board diagnostic function? EDIT: NO THEY DONT, A BAD TPS DOES.
I will be testing my TPS tonight. What is that vac. line for on the TPS connector anyhow?

[nando]

it has nothing to with the chip

also not sure what you mean about "newer style" TPS - there's only one kind for the E30 M20B25, and it's definitely adjustable.

the vac line goes to the purge canister solenoid

[Sagaris]

As far as "newer style" TPS goes: I was under the impression that older M20's had 2 micro-switches which the throttle comes into contact with at WOT and at idle. I cannot see any micro-switches on my car, What I see resembles a potentiometer type throttle position sensor on the underside of the throtle body. I guess its possible that there could be 2 micro-switches inside part #24 below (the part I have on my car) and that I could be completely wrong altogether.



I will have to check over the Bently for adjustment info later on unless anyone is willing/bored enough to post some information up about it.

[nando]

that was probably etas that had 2 seperate switches

the B25 still uses 2 switches but it's all built into #24, it's not a potentiometer.

the bentley does cover adjusting the TPS

[Sagaris]

Thanks for clearing that up! I definitely appreciate your experience and insight in this and many other threads I have encountered here.

[sarcasmkillsme]

it has nothing to with the chip

also not sure what you mean about "newer style" TPS - there's only one kind for the E30 M20B25, and it's definitely adjustable.

the vac line goes to the purge canister solenoid

Actually his stomp test problem probably is the chip. Mark told me awhile back that if I ran his 173 chip in a 525 DME I would loose some diagnostic functions. Try putting the stock chip back and stomp test again.

[nando]

interesting. hardware wise, if you compare them side by side, it's impossible to tell the difference.

[Sagaris]

My understanding of the 173 DME vs 524 DME is that the 524 is able to generate a few more trouble codes than the 173. Just throwing that out there. My knowledge of an EPROM performance chip is that it is just a storage device for the fuel and timing maps. It doesnt seem like diagnostic code systems would be included in the same chip but rather some other part of the DME

[Sagaris]

I checked my TPS today. The idle switch is being switched but the full throttle switch is not. This would explain the stomp test not working. Does the ECU read the full throttle switch signal to go into open loop and ignore the oxygen sensor input or do anything different fuel+timing related?

[jlevie]

I checked my TPS today. The idle switch is being switched but the full throttle switch is not. This would explain the stomp test not working. Does the ECU read the full throttle switch signal to go into open loop and ignore the oxygen sensor input or do anything different fuel+timing related?

Yes

[Sagaris]

It's too bad the throttle body has to come off to adjust the switch. Looks like I will be ordering a throttle body gasket. I appreciate the help as always.

[nando]

it doesn't really, you just need to remove the airbox, and use a short screwdriver.

also, the gasket can be reused as long as it's not torn.

[Sagaris]

You can access one of the mounting screws for the TPS but the manifold blocks the other one. I would be impressed if someone has performed this without removing the throttle body.

I got at it today, took the throttle body off and replaced the TPS with a used one that works. I replaced my PCV hose while I was at it. I had a used one that looked better than the one on the car (It was split open on the valve cover gasket side). I had it siliconed before to help prevent any vac. leaks but it must have leaked regardless since replacing it fixed one of the tiny vac. leaks I have. Part throttle performance and response is improved and with the functioning TPS the stomp test works again.

I have done a stomp test before, but it just hasnt been working recently. It turns out the TPS I removed only occasionally worked at full throttle. I tested it with my continuity tester 20 times or so and was able to get it to work 3 times.

Im going to see what the vacuum gauge reads and see how much it is up from 15 inHg since fixing that vac. leak.

[Kershaw]

i tried, but in the end i just removed the throttle body. its only 4 nuts. i didnt disconnect a lot of the lines either. i just bent it back to access the tps.

[Sagaris]

Yep, I left the brake booster lines, coolant lines, and the evap canister line in place and removed the PCV, ICV, Intake boot, and throttle cables.