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What happens if there is NO speedo input signal to LH2.4?

dkrause

Member
Joined
Sep 2, 2012
I am installing a engine with a LH2.4 into a car that does not have an electronic speedometer, what does this signal do in the ECM?
Will the car run without this signal?
And if not is there any work around?
 
It will wig the f out! My speedo was intermittent and i could feel a huge difference in performance when it did decide to work, vs not working. It didn't like idling either without the signal. The Lost art of could better describe why it needs and what it needs. My suggestion of a work around is a simple drive-shaft speed sensor kit. Summit sells them. Its a adjustable collar with magnets and a mount for the sensor. Its like $25 , i have one in my tool box i was going to use.
 
In another thread it was said that the idle would hang at ~2000rpm after driving. I had noticed this on our 24hr lemons car that ran LH2.4...come off track and leave it running, it ALWAYS wanted to idle high, 1500-2000rpm.

I'm not sure why but we added a turbo, changed out the computers for the Turbo variety, and I haven't noticed that issue since the turbo conversion.

We definitely don't have the speedo signal from the rear end hooked up to anything, and the car runs/drives fine. There's still a gauge cluster but the speedo is dead. We just use it for the water temp and gas gauges.
 
When I didn't have it hooked up sometimes it would idle a bit high, but then I'd tap the throttle and it would come down. You can't use a 2.2 ECU on a 2.4 harness. For one the 2.2 ECU has a smaller plug deal(compared to lh2.4 ECU). It is the same as the EZK plug. 2.4 ECU's have a bigger longer plug.
 
If I was to take the output directly off the rear end ring tone to the ECM would the signal work?
Or does it need some signal conditioning?
Thank for the comments.
 
If I was to take the output directly off the rear end ring tone to the ECM would the signal work?
Or does it need some signal conditioning?
Thank for the comments.

No it needs to go from the rear end to the speedo then to the ECU. The speedo does something to the signal that the ECU needs. Not sure what but could be just a resistor or some sort of impedance changer. Could it be just power the that the cluster provides. You possibly could figure it out if you had it all hooked up and started checking stuff with a volt meter and ohms. I'd first look at the schematics..


THe other thing the speed signal does for the ECU is above a certain speed when you let off the gas the ecu cuts fuel to the injectors, if it doesn't have the signal fuel isn't cut all the way. I noticed this on my wideband before and after I hooked up the speed sensor. When it cuts fuel the car slows down a little bit faster then if it doesn't.
 
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No it needs to go from the rear end to the speedo then to the ECU. The speedo does something to the signal that the ECU needs. Not sure what but could be just a resistor or some sort of impedance changer. Could it be just power the that the cluster provides. You possibly could figure it out if you had it all hooked up and started checking stuff with a volt meter and ohms. I'd first look at the schematics..

I'd really love to know what that is because from where I'm standing, 2.4 never had any functionality that would require know what it's speed is. For what I know, cruise control is handled by a seperate computer. Anti-lock functionality is controlled elsewhere, and that uses different sensors anyways. And 2.4 never had any traction control.

So I'm having a hard time believing that 2.4 needs a speedo signal.

But if I'm wrong, please correct me. I've been wrong around here plenty of times before.

THe other thing the speed signal does for the ECU is above a certain speed when you let off the gas the ecu cuts fuel to the injectors, if it doesn't have the signal fuel isn't cut all the way. I noticed this on my wideband before and after I hooked up the speed sensor. When it cuts fuel the car slows down a little bit faster then if it doesn't.

Uhhhh.... I think it uses the RPM sensor and TPS for that job. Looking at my AFR gauge, the engine always resumed in jecting fuel when the RPM dropped below a certain point. Go put it in Nuetral on the freeway and see what your wideband says.
 
From what I've heard....it may be wrong but the only problem with running without the speedo signal is that the car doesn't go into decel mode...runs rich when coasting down hill or off the highway.
 
So I'm having a hard time believing that 2.4 needs a speedo signal.

It's there for a reason and will throw a 3-1-1 code if it's absent.

From what I've heard....it may be wrong but the only problem with running without the speedo signal is that the car doesn't go into decel mode...runs rich when coasting down hill or off the highway.

I don't think that is correct. The decel mode is engaged when the throttle is closed, but RPM's are above a certain point. IIRC, it's 2K.
 
I don't think that is correct. The decel mode is engaged when the throttle is closed, but RPM's are above a certain point. IIRC, it's 2K.
Yeah pretty sure that still works, AFRs head towards 20.9% O2 on lift-off decel above ~1500-2000rpm(?). We have an LM-1 wideband in the lemons car w/LH2.4 lacking speedo signal to ECU.
 
Thanks lots of good stuff here. I have checked wiring diagram and it certainly shows the signal coming from the Speedo cluster where as the ring tone signal is paralleled to the ABS but not ECM, therefore I beleive the Speedo output must be modified in some way from the original. as I don't have a car with the Electro speedo I can't stick a scope on the lines to see what it looks like.

So I will complete the install without the speedo input and see what happens (paying special attention to idle and coast down).

THX
 
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