Reduced RPM Limit causes??

[vosadrian]

Hi All,

I have only just registered here, but have found this forum valuable for info on the Elise in the past.

At the moment I am having a problem with an Exige I have been working on (Toyota engine). This car has a fair few mods including some ECU mods that I am involved in, and this is where I am running into a problem.

The car generally runs fine, but if you give it a fair bit for a while, the stock ECU enters a state where it rev limits the engine at about 6000RPM. Once this state is entered, the ECU will limit the revs regardless of engine load, and the only way to clear it is to shut down the engine (ECU off) and when the engine is restarted it will run perfectly until 10 minutes later if you drive it hard when it will do the same thing. It is inconsistent... somtimes it happens in 5 minutes... other times it take 30 minutes, but it always happens. There is no check engine light, and no fault code when we connect an OBD scanner. I wish we were getting a code so we atleast then knew where to look to fix it!!

My research here and elsewhere reveals that this is standard if the engine gets too hot or is not yet warmed up, but the coolant temperature is difinately in the normal operating range.

Also, I have seen some rare posts on forums about standard cars that enter the same state, and are reset by restarting the ECU, but there is no reference to a possible cause. Clearly the mods on this car have induced it to be so repeatable, so it is much more of a concern for us than in other cars where it may be a once off.

To me it is obvious that the standard ECU limits RPM under more coniditions than just coolant temperature, and I am really just trying to find out under what conditions the ECU implements this lower engine limit, as then I will have some direction to go in getting rid of it.

I am hoping that someone here may know more about the ECU than I have been able to find and may be able to add something, or is there anywhere I can look to find factory manuals for this car that may have some diagnostic information with reference to this problem.

I suspect it may be something to do with a crank signal interceptor that we use to pull alot of timing out of the engine (forced induction) that may be confusing the cam phasing software, but I really just want to find out if there is any list of things that can cause the rev limitting to be reduced.

Thanks in advance for any help!!

-- Adrian

[MotorCade]

pm shiv@vishnu. My car has had a problem like this, it was throwing a code for cylinder one injector error. Turned out to be a shorted wire.

Cade

[TimMullen]

Originally Posted by vosadrian

Also, I have seen some rare posts on forums about standard cars that enter the same state, and are reset by restarting the ECU, but there is no reference to a possible cause.

My post was one of those. It happened once to me, on a normal day, normal operating temperatures, etc. Next time I started the car it was back to normal, and has never happened again.

Sorry that I have no more insight into the problem...

[charliex]

you need a tech 2 , the car is most likely entering limp home mode, which is the limiter you're hitting, it'll do it for any condition that might cause damage, which basically means just about any sensor out of whack.

an obd ii scanner may not tell you all the codes that are available, or whats going on, did it show any freeze frame data available ? what sort of reader are you using ?

are you in SLO by any chance?

[vosadrian]

Thanks for the comments!!

I am in Australia. I am using a Carman scan. It does not have anything in it specific to the lotus, but it does have OBD scanning, and we have picked up another code that we were previously causing (P1302) with this equipment. It is however not ideal. When you watch live data it is very slow, and has errors regularly. It will read the correct RPM and them jump suddenly to anotehr much higher RPM which the engine is not doing, yet the engine is running perfectly at the time. Other data acts similarly. Is this tech 2 expensive?

Previously when we got the P1302, the CEL came on, and the car started missing. If we stopped the car and restarted, the car would run fine, but the CEL would still be on until we cleared it with the Carman scan. We identifyed and fixed this fault because we knew where to look, but we have not got any info on this latest fault.

It is most surprising to me that the engine would RPM limit without any CEL. I too suspect it is a limp home mode, but normally if an engine enters limp mode, there is a CEL or something to reflect this. Also, in most service manuals, there is a diagnositc procedure for identifyin fault symptom solutions, but I have never seen the service manuals for the lotus. Is this available anywhere? A list of conditions that cause the reduced RPM limit would be great!!

I am suspecting that the factory ECU is seeing the 7 degrees of timing we are pulling out of the factory crank sensor, and that this may be playing havoc with the cam phasing control which would be comparing the cam position sensor to the crank position sensor, and wondering why it cannot hit its target. If this is the case we may need to find other ways to control the ignition timing, but I really want to find out if this is the case.

Thanks again!! Any further comments appreciated.

-- Adrian

[charliex]

its about $2000 usd, which is pretty cheap for an oem scanner

the lotus tech web has all the docs available for diagnostics

P1302 is a misfire that may cause catalyst damage (thats the official lotus wording)

some scanners aren't all that good, the problem you see is all too common with 'consumer/prosumer' level stuff, the tech 2 will let you see all the lotus stuff, perform sensor testing etc. maybe a local dealer will lend you one for a bit

i agree its suspicious its in limp home with no MIL but it sure does sound like it.

unfortunately the tech webpage http://66.139.73.25/amember/index.php
is notoriously flakey at the best of times, lotus are barely scraping by on the legal minimum as it is.


edit: i just remembered, if the car is in limp home mode, it will also go into open loop mode, which a generic obd ii tool should tell you
edit2:
limp homes
p0201/2/3/4 injector open circuit 1/2/3/4, sets limp home, open loop
p0300/1/2/3/4 cylinder misfire random/1/2/3/3 ,sets limp home, open loop, deactivate 1/4 or 1/3 cylinders

those are the ones listed as setting limp mode

[vosadrian]

I suspect it may be related to P0300. It may be that there is some jitter in the signal out of the interceptor that I will have to look into reducing to see if it makes a difference. It may be interpretting some small inconsistency in the output pulses as missfire. This product has been used on many engines in the past without this problem, but most engines don;t rev like this one also!!

-- Adrian

[Photochromatic]

Hi Adrian,

DO you have a resolution to this one yet? Mine has just started doing the same thing. An ECU reset at the dealer fixed it temporarily, but the problem is back again.

Darn- I have a track day booked on Thursday too.

-Richard

[sandsmuseum]

Are you sure you have eliminated the temperature as the limiting factor on the rpm?

There was a similar thread in the Lotus Club International forum, someone was limited to 6000 rpm and it was random but fairly consistent.

It was suggested that the coolant temperature sensor was bad and sending intermittant data back to the ECU. There was not final resolution to the problem posted.

I suggest that if it is a limp home problem, the ECU will throw an exception. Since there is none, I suggest investigating the temperature sensor some more.

Michael

[Photochromatic]

Thanks Michael,

I'll suggest that to the dealer.

The first time it happened, I took it to the dealer who hooked the computer up. The computer said "Timing Retarded". A reset via the computer fixed it for a while.
I took it for a run last night - if I turn the engine off and then on again, I can get it to go on the cams maybe once, before it starts to play up again.
I have a feeling I might know what caused this in the first place - the service agent had another Elise with similar issues and was stumped, so he measured the square wave at my cam actuator with a 'scope, to see what a "normal" one look like. That is when I started having problems....

I am wondering whether the current draw from the 'scope confused the ECU, but then I would expect that the reset would have fixed it.

Apparently, there is a reflash due for the '05 ECUs which among other things, reduced the ECUs sensitvity to some misfire sensors. I don't have a misfire, but I am hoping that the reflash might help.

Cheers
Richard

[TitoLugo]

I had a similar problem a while back just after jumpstarting the car. The cel came on and I wasn't able to go in the second cams. After getting a obd2 scan there was an error that I can't remeber the exact message but it was something like "fault in the timing retard actuator". After looking for a while I found one of the fuses on one of the two fuse boxes located on the engine compartment burned. Changed it an problem solved. I hope that would be your problem.
Alberto

[EU111R]

I went out for a ride today and after a proper warm up gave full throttle. Everything fine until 6000rpm: then the red light came on and rev limiter cut in just before the "big cams". It was the first (and so far the only) time it happened (almost 2 years and 8000 miles w/o problems) and I'm a bit worried as my warranty will be running out shortly. Has anybody got any update on this?

Thanks

John

[Photochromatic]

Mine turned out to be an ECU fault, and a faulty oil-control valve in the advance mechanism. Difficult to tell which one caused the other, but the ECU probably went first.

The standard Lotus diagnosis thingy only returned a "Timing Retarded" error. Eventually some kind of generic dignostic tool was hooked up and returned 13 separate error codes.

Get it looked at before the warranty runs out. The ECU is expensive, and the oil control valve work is time consuming.

[EU111R]

Thanks for your feedback Photochromatic

Was your problem a permanent one or just sporadic? If sporadic, how often would it happen?

Cheers

[EU111R]

Sorry Photochromatic, I just read the description of your problem in one of your previous posts. Pls disregard my questions

I just had a thought: I have started the car the other day after 3 months of complete inactivity, during which I left the battery disconnected. Am I wrong or does the ECU have to "learn" something during the first hundreds of miles to auto-calibrate properly? During the same drive, just before the problem occurred the engine stalled (to my surprise) at a traffic light...
Maybe this problem is prone to happen during this period. Was your car in a similar situation when the problem occurred?

Cheers

[charliex]

the ecu is capable of retaining information for a very long time.

it relearns very quickly , a few minutes usually.

stalling is very common, it seems to be a lotus trait my DBW does it too, on the non DBW the cable stretches over time and you can adjust the throttle quadrant screw in the engine bay to fix it