2G Limp mode

[Iceman8079]

Looking at buying 98 gst 80xxx miles couple upgrades buddy says it goes into limp mode won't go over 20mph is car worth 1000 no rust anywhere

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[curt-s]

No rust anywhere? It always lurks inside rockers and fenders, especially for something that sits in the rain.

 

[1990TSIAWDTALON]

You could replace the factory transmission computer with a ForcedFour shift box for around $350. It sounds like the factory unit bit the dust. Check all wires going to the transmission (pulse generators, kickdown servo etc) for broken places or not connected. Those will throw it into limp mode as will capacitors going bad in the TCU.
I am not sure if there are remanufactured units available but I did find THIS ONE and I have a MD762042 TCU for a 97-99 FWD around here somewhere. Let me know if I can help anymore. If that is all that is wrong with it, it sounds like a deal you could pick up and use or flip.
Marty

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[steve]

buddy says it goes into limp mode won't go over 20mph

Limp mode in the automatic transmission or limp mode in the ECU?

 

[Iceman8079]

Thank u guys for info and support. I will keep in touch.

 

[1990TSIAWDTALON]

Limp mode in the automatic transmission or limp mode in the ECU?

Can the ECU also go into Limp mode @steve ? Another thing that I wasn't aware of???

 

[habitatguy187]

Can the ECU also go into Limp mode @steve ? Another thing that I wasn't aware of???

Yes. Ecu limp mode is just open loop operation though I believe

 

[1990TSIAWDTALON]

Ah hah.
ECU Limp = Open Loop Operation
Thanks, now that makes sense.

 

[Iceman8079]

So I bought a 98 eclipse gst. Owner before said it won't go over 25 30 mph. Replaced map sensor no boost leak or vacuum leaks anywhere. Just wanted to see thoughts on maybe the old cats being bad would cause this issue.

 

[pauleyman]

So I bought a 98 eclipse gst. Owner before said it won't go over 25 30 mph. Replaced map sensor no boost leak or vacuum leaks anywhere. Just wanted to see thoughts on maybe the old cats being bad would cause this issue.

Don't guess. Obectively diagnose.
Any codes? Do a boost leak check.
Followed by compression. Leakdown. Etc.
At least do some basic diagnostics and tune up.

 

[pauleyman]

96 and newer cars are all obd2. 95 up for dsm. No reason to not use that to your advantage . Diagnostic tools are very cheap. Simple Bluetooth dongle and phone app is under 40$. Will tell you lots about what the car is doing

 

[steve]

Ah hah.
ECU Limp = Open Loop Operation
Thanks, now that makes sense.

No, ECU Limp mode = CEL on. Depending on what failed the ECU will do different things, IIRC the FSM describes the various faults and how the ECU limps from them.

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[habitatguy187]

Depending on what failed the ECU will do different things, IIRC the FSM describes the various

Awesome info from you as usual. I know OP has a 2g, but do you know if a 1g ecu is similar?

 

[steve]

do you know if a 1g ecu is similar?

Not as sophisticated as the 2G. This table is in the 1G 1990 DSM Technical Manual which every DSM owner should have and read regardless of what year DSM they have and if you have a 2G also read the 2G version.

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[1990TSIAWDTALON]

If it happened to be a TCU issue, there is one for sale in this ad.

https://www.dsmtuners.com/marketplace/aftermarket-oem-parts-taking-offers.4551/