Altitude? Misfire

[F355GTS]

98 Ex Race SLR, Minister VHPD Engin with KV6 TB's and Mems ECU

 

Having had the problems of misfires at a couple of trackdays in the UK and borrowing Jue Thompson's ECU which cured it the car was an absolute pig to drive at Spa.

 

Massive hesitation/ stuttering trying to pick up from anywhere below 4k revs until about 5k then it was like a turbo cut in with full power, it made it very interesting trying to hold a balanced throttle through some of the curves and then gentle acceleration away would turn into very impressive power slides.

 

The car also seemed very un-cooperative in 5th and 6th above 6.5k revs in as much as it didn't want to go there

 

I've read before that the std Mems map is particularly bad at altitude but Spa is only around 470M above sea level could it be this?

 

Things that appear to be OK are

 

Alternator 14.4v

Plugs, Leads, Distibutor no signs of Arcing or damage, plug gaps OK

Car has new Crank Sensor, and Throttle Pot

Fuel was new Optimax am and Total SUL pm

 

I'm waiting for DVA to supply an Emerald but hopefully I've eliminated the ECU by fitting another (known) good one.

 

Are VHPD Plugs leads different to std Rover K series or can I just pop dowm the Rover dealer for a set?

 

Any other advice gratefully received

 

 

 

 

 

 

Mark

[philwaters]

Not sure how relevant it is, but when I took my x/flow on carbs over there it was way down on power due to the Altitude, but it never misfired. I expect that is more down to the carb way of life - chuck in this much fuel, and a bit more for luck.....

I read somewhere on here that someone had the same problem with a K when abroad - have you done a search?

 

 

Phil Waters

You mean you can drive these?

I thought it was just there to polish 😬

[Paul Ranson]

I don't believe Spa is sufficiently high for altitude to be an issue, especially given the extreme symptoms.

 

Paul

[Asklepios]

I think Paul is correct,as the pressure difference is about the sea level change from high pressure to low pressure storm conditions in the UK. However if the engine was set up on the rich side anyway ,and you had some pre spa difficulties , then the decreased baro pressure may have amplified your difficulties.

If your new map is weaker at the prob. point ,and your symptoms disappear at Spa next time, then your diagnosis was prob. accurate.

[V7 SLR]

Was the one you borrowed another MEMS? If so, there is increasing evidence that a MAP sensor mounted inside the MEMS box can fail in the VHPD application, causing exactly the mode of failure you describe. There is also some opposition to this (just trying to offer a balanced view).

 

If you changed your MEMS for Julian's then I'm guessing his was OK because it was new, which means the MAP sensor hasn't been subjected to the standard SLR staccato idle for long. Thinking about this logically, a pulsing idle will cause the MAP sensor to oscillate. I have no idea about the MAP sensor's construction with regards to whether it could suffer from mechanical failure, but if it can, it would this mode of failure is likely in the VHPD as the VHPD subjects it to quite a harsh mechanical "test".

 

You confused me a little where you say this

I'm waiting for DVA to supply an Emerald but hopefully I've eliminated the ECU by fitting another (known) good one.

 

Are VHPD Plugs leads different to std Rover K series or can I just pop dowm the Rover dealer for a set?

---

It sounds like you have found the problem (the ECU) yet you are still trying to find the cure?

 

Stick with it. The M3DK will cure all your evils.

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[F355GTS]

V7

 

Problem started a couple of months ago with a stutter/ misfire on a balanced throttle at 6.5k revs. On a trackday a couple of weeks ago the problem was evident and I swapped the ECU for Jue's Mems unit and the problem went away so assumed Peter C and others were correct that the Map sensor was the problem. Next time of running the car was at Spa and problems are much worse and across a wider rev range which if it is the ECU again is worrying because a) it's quite new and b) it's Jue's!!!

 

 

Mark

 

 

 

Mark

[V7 SLR]

Ah, understoand now... you're still using Ju's and that is playing up..!!

 

Hmm, I still believe the problem is MEMS related but the only way to tell for sure is to borrow an M3DK. As they're as rare a hens teeth, I guess you'll need to be great friends with someone before they'd lend you their's...

 

I happen to have one and would be willing to let you play with it if you fancy bringing the car up to Worcs (Redditch - I'm guessing you're down South somewhere relative to me). I've got a few maps available (one is bound to suit your car) and as Redditch is a purpose-built race track (don't care if plod's reading) you'll be able to give it a sound thrashing around here to determine whether or not it really is the MEMS.

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[F355GTS]

thanks V7 seems i may have jumped the gun with original info, seems No3 plug is v.v. black, am fititng new ones as we speak so will advise further

 

Mark

[F355GTS]

Right well that helped, new Dizzy cap, HT Leads and Plugs although it was definitely the plug in No 3 at fault, seemed to be failing under load. Will be testing on Saturday to see whether that was the original fault ie not ECU. The good news is that Ju's ECU seems fine, still want an Emerald though

 

Not sure the plugs are right type see seperate post

 

Mark

[Steve-B]

The VHPD misfires over 3000 ft in altitude in my experience in this years' Targa-Liege.

 

I attribute it to several things:

 

1) still have the MEMS, will upgrade to Emerald when have a job

2) plugs fouled up, had to regap and clean then twice

3) wrong plug gap, now using .90 instead of .98

 

these all added up..... 🙆🏻

 

Go team GBR ❗

[Mick Day]

From what I understand the VHPD engine was produced for a UK race series & the MEMS supplied by Rover didn't have any barametric compensation. I saw the same symptoms on Andy Graham's SLR 2 years ago at the Ring (similar altitude). Just about everything was changed on the car in an attempt to get him running but to no avail. A similar problem happened to a new SLR on the Spannish trip in 2001. Return to the UK & no problems. Caterham are aware of the problem & have now fitted a MBE unit.

 

A particularly low barametric pressure day at Spa would therefore cause the MEMS to over-fuel resulting in the symptoms you describe. As the Emerald (& most other aftermarket ECU's) has built in barametric compensation you'll be OK.

 

Mick

[Warren S Smith]

Mine was the SLR with ECU problems. Changing to an Emerald with V7's map has made the car immeasurably better.

[yankeedoodoo]

Why does an Emerald make a difference @ altitude? The unit does not contain a specific, dedicated altitude compensation strategy/program.

[F355GTS]

BU**er

 

So the new plugs/ leads/ Disty cap cured the problem with the misfire at lower revs but the hesitation on balanced throttle is back to haunt me, this with Jue's ECU, new throttle pot, crank sensor, Plugs, HT Leads and Disty Cap. The only thong i can think of now is fuel starvation.

 

I have the high pressure pump in a std Ali tank, will start stripping tomorrow and see if that's OK, clean etc. What else should i be looking at/ for??

 

Mark

[Mick Day]

Why does an Emerald make a difference @ altitude? The unit does not contain a specific, dedicated altitude compensation strategy/program.

 

I'm not too sure about the software in the Emerald but I assume it's similar to the GEMS. There is an air pressure sensor in the box which is pre-programmed to alter the fuelling map by a percentage when barametric pressure changes. A quote from the GEMS manual:

 

"Manifold or Barometric pressure

The standard product uses an internal 105 kPa pressure sensor that may be used for barometric pressure compensation, or Manifold Absolute Pressure measurement via a pipe to the inlet manifold."

 

The MAP sensor setting must be off to allow this to function.

 

Mick

[V7 SLR]

I do not believe the Emerald has any barometric sensor (supported by my not finding any hole where any such sensor would read atmospheric pressure through the casing), which makes it doubly excellent as the Se7ens List Euro2002 tour had us driving over the Swiss Alps. Those with Emeralds just worked faultlessly. Me, on a MEMS, regardless of altitude, had the first 10% of throttle and the last 5% with everything inbetween being useless.

 

Bearing this in mind, is altitude such a problem if the ECU was properly mapped to begin with?

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[Mick Day]

The GEMS ECU has a hole in the casing, about 3mm in diameter. Regardles of whether the ECU is properly mapped or not any atmospheric change will affect fuelling. Maybe the MEMS is so far out (witness other examples) that any reduction in atmos. makes it far to rich, resulting in the problems discussed. In any case dump it & get something else.

 

Mick

[Julian Thompson]

Just thinking very carefully about this and trust me, I am no expert but was intreagued by the idea that the Emerald was better "at altitude".

 

Certainly I'm pretty sure it has no barometer in there, and certainly a proper map only has a narrow window of deviation between right and wrong regardless of whose it is; there is no doubt the MEMS is a poor match for the engine and that many of its strategies are flawed badly in the Caterham application.

 

But.

 

Why the inherent poor performance at altitude? Well, I wonder if the very fact that the MAP sensor is sensing vaccum from the engine is the reason. I mean, if the ambient air is at a lower pressure then surely this will result in a different reading at the MAP sensor and so cocked up fuelling and ignition maps. The Emerald, by contrast, doesn't take this info and so doesn't "know" you're at Spa, which by all accounts shouldn't be intrinsically high enough up to provide a problem with the maps unless provoked as described above in the case of the MEMS?

 

Probably wrong, but worth a stab, eh?

 

Mark: Do remember that my car displayed the following ECU faults from new:

 

1) Unable to run unattended from cold.

2) Massive, massive flatspot (dangerous) at about 3.4-4k when you snapped open the throttle. This problem only happened in certain condtions which I wasn't able to totally define since I got cheezed off with the unit and replaced it after 4 weeks........

3) The car pinked its cock off in top under a light load.

[yankeedoodoo]

Last week I received an e-mail from Karl @ Emerald who informed me that, "The ecu doesn't have an internal barometric pressure sensor but one can be fitted externally. The pressure compensation table can then be configured to give the correct injection/ignition corrections to compensate for changing pressure/altitude. The injection compensation needed is a known amount but the ignition compensation (if required) is engine dependant." Knowing this, I was most curious as to why the Emerald worked better @ altitude. And I ordered one! I frequently motor from sea level to 6500 ft. A report will be submitted after some rigorous testing!!

[V7 SLR]

Excellent..!!

 

I understand that some ECUs only take barometric readings at start-up, but this might only be for ECUs that use the same MAP sensor for instantaneous MAP readings. I'm interested to know how often the Emerald takes barometric readings.

 

I ask this because in one drive it is not inconceivable to start at the bottom of the Alps and drive over the top in one go. Makes a mockery of the "only at start-up" principle really.

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[yankeedoodoo]

V7 SLR: The standard Emerald has no barometric sensor to read. Also, it does not have a MAP sensor. Karl is presently developing the MAP software and expects that it will be available around Christmas. The software download for MAP will be free to all existing owners/users.

[V7 SLR]

OK, maybe I should have said "I'm interested to know how often the Emerald will take barometric readings."

 

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours