Fuel/Ignition cut @ 5500 RPM only on dyno...

AvivB

New member
Hi guys,

I have a weird issue that I cannot figure out and I need your help.

I have ST182 (FWD) with engine from ST185RC/CS.
When I swapped it, I also took the ECU, boost-pressure sensor, coil, MAF and igniting controller from the ST185 and put them in.

On the road, there is absolutely no problem and I can rev/boost all the way up to the red line at 7000 rpm.
But when I go on the dyno, it get fuel or ignition cut at 5500RPM!.

There are no CEL codes...
I tried to go back to stock boost levels (bypassing the boost controller leaving only the stock actuator connected)... no change...
I try to disconnect the ABS fuse... no change...
I try to disconnect the vacuum/boost line from the boost-pressure sensor... no change...

Any ideas?
 

underscore

Well-known member
What kind of dyno, and how is it set up? Are you sure you're hitting fuel cut and not just hitting a limit of your fuel system? Dynoing tends to be done in 4th gear so yo may not notice it on the street because 5500 in 4th is going to be a high speed/load on the engine.
 

AvivB

New member
Dyno type is DynoPack (the one who attached instead of the wheels).

We started on 4th and we thought we hit the speed limiter (as the ECU is the Japanese version) so we recalibrate the dyno and try again on 3rd but got the same issue.

AFR reading were super rich so I don't think it was a fuel issue.
(as I wrote, it also happen on stock boosting levels so the fuel system should hold it).
In addution, when I do it on the road with full boost, it stay super rich all the way to 7K RPM.
 

AvivB

New member
There isn't any setup like that in the dyno... and the dyno cannot stop the engine from reving.

I've started to suspect that the ECU have some kind of "no load" rev limit and it somehow notice the almost no-load condition on the dyno.
But as far as I know, the only way the ECU can detect load is by throttle position and this was fully open.
 

klue

New member
AvivB":10g77iku said:
There isn't any setup like that in the dyno... and the dyno cannot stop the engine from reving.

I've started to suspect that the ECU have some kind of "no load" rev limit and it somehow notice the almost no-load condition on the dyno.
But as far as I know, the only way the ECU can detect load is by throttle position and this was fully open.


Yes there is, its called " set speed" its on the main streen which displays your real time output. You need to have the gear ratio calculations done or it wont work properly.

The ECU does not have a no load rev limit, or else it wouldnt rev past 5500 in netural. The ECU detects load from the AFM nothing more.
 

AvivB

New member
We did the dyno gear ratio calibration twice, first of 4th gear and then on 3th gear when we thought we hit the speed limiter of the Japanese ECU...

I'm away from my car for the weeked but after it I'm going to try reving in natural passed 5500.
I have a vague memory that once I tried to do so I got CEL code...
 

klue

New member
AvivB":kkx3obsj said:
We did the dyno gear ratio calibration twice, first of 4th gear and then on 3th gear when we thought we hit the speed limiter of the Japanese ECU...

I'm away from my car for the weeked but after it I'm going to try reving in natural passed 5500.
I have a vague memory that once I tried to do so I got CEL code...

speed cut is 180 on the jap ecu, 3rd gear shouldnt be doing that if my memorys serves.

if your getting a cel code and there is a rev limit, sounds like a knock code (52 again if the memory serves)
 

brutekiller787

New member
Just a thought but what if the speed sensors on the back wheels are detecting a difference in speed and the rc ecu limits the revs?

Not sure if they had that back then but wouldn't that be some stuff.
 

AvivB

New member
brutekiller787":jif12a75 said:
Just a thought but what if the speed sensors on the back wheels are detecting a difference in speed and the rc ecu limits the revs?

Not sure if they had that back then but wouldn't that be some stuff.

There is no 2nd speed sensor.
The only one exist attached to the gearbox.
 

AvivB

New member
brutekiller787":33pp65ql said:
There are wheel speed sensors if the car has abs
You're referring to the ABS sensor exist on all wheels.
One of the tests we did was to disable the ABS system by pulling its fuse out... but it didn't help.
Also, as far as I know, there in no connection between the ABS control unit to the ECU so the ABS cannot cause rev limit.
 

AvivB

New member
I did a try today to rev up in natural... the rev limiter kick in only at 7K RPM... (as it should).
So I'm back to square one as I have no idea what happen on the dyno... :(
 

AvivB

New member
Well, I can but...
I'm in Israel and there is only one place who have a DynoPack!!!
I don't trust the rollers dynos, I'm always afraid I'll find my car bouncing the closest wall...
In addition, the one who holds the DynoPack is a friend so I'm not paying for it...

Also, I want to figure the reason as I can not imagine a way the dyno csn be blamed for the fuel/ignition cut...
 

klue

New member
klue":1as79ica said:
AvivB":1as79ica said:
There isn't any setup like that in the dyno... and the dyno cannot stop the engine from reving.

I've started to suspect that the ECU have some kind of "no load" rev limit and it somehow notice the almost no-load condition on the dyno.
But as far as I know, the only way the ECU can detect load is by throttle position and this was fully open.


Yes there is, its called " set speed" its on the main streen which displays your real time output. You need to have the gear ratio calculations done or it wont work properly.

The ECU does not have a no load rev limit, or else it wouldnt rev past 5500 in netural. The ECU detects load from the AFM nothing more.
 

AvivB

New member
klue":1yli2qf2 said:
klue":1yli2qf2 said:
AvivB":1yli2qf2 said:
There isn't any setup like that in the dyno... and the dyno cannot stop the engine from reving.

I've started to suspect that the ECU have some kind of "no load" rev limit and it somehow notice the almost no-load condition on the dyno.
But as far as I know, the only way the ECU can detect load is by throttle position and this was fully open.


Yes there is, its called " set speed" its on the main streen which displays your real time output. You need to have the gear ratio calculations done or it wont work properly.

The ECU does not have a no load rev limit, or else it wouldnt rev past 5500 in netural. The ECU detects load from the AFM nothing more.

As far as I understand from the dyno guy, this is only set the graph X axis max value.
You first calibrate the gear ratio (so the dyno can calc the rpm from the wheel speed) and then you tell it up to what rpm values to expect.
No matter what you will put there, it won't prevent from the engine reving if you press the gas peddle...
 

underscore

Well-known member
AvivB":1ujkqudg said:
Well, I can but...
I'm in Israel and there is only one place who have a DynoPack!!!
I don't trust the rollers dynos, I'm always afraid I'll find my car bouncing the closest wall...
In addition, the one who holds the DynoPack is a friend so I'm not paying for it...

Also, I want to figure the reason as I can not imagine a way the dyno csn be blamed for the fuel/ignition cut...

If you secure the car properly it won't go anywhere. The DynoPack may be free, but if the issue is with your car and not the dyno then you might blow something up. One pull on a different dyno should tell you which of the two is causing the problem.
 
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