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Ex rally car 3000rpm limited no sure why

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Hi I have a Vauxhall nova ex rally car with a 2.0l redtop engine in it in the workshop it’s had the engine out and rebuilt a few times got a different Ecu it’s had a lot of work done on it but the car won’t go past 3k rpm it’s been to tuners and nobody seems to know why but the car seems to hit a limiter rev upto 3k and sounds like a hard limiter is stopping it going past could someone help please

What ECU?

Can you post the map and/or data logging?

I worked on a 1990's era F1 car with a Judd V8 that had a similar problem. The issue turned out to be low-impedance injectors were fitted, and the ECU was swapped to a version (EFI Euro-6) that would only work with high-impedance injectors.

We replaced the injectors with high-impedance injectors, but the spray pattern was so different that the car wouldn't transition off of idle, it would only rev to about 4k RPM (idles at 2500-3000 RPM).

Final solution was to fit external injector drivers that could run peak-and-hold low-impedance injectors, but present a high-impedance interface to the ECU. Car ran perfectly without remapping.

Clues for us -- the Battery Voltage dropped whenever the throttle was opened (looked like an inverse of the throttle trace in the data). Spray pattern was noticed by observation high-mounted injectors onto a slide-valve throttles -- easy to see a stream / puddling vs. fog with the original injectors.

Another thought:

Does the ignition timing track the commanded timing as the RPMs increase? Incorrect wiring, or ECU setup can result in an engine that runs, but can't run at all engine speeds.

Are all sensor inputs (especially throttle position, and manifold pressure) showing reasonable values. Improper configuration / calibration with a new ECU could result in incorrect fueling if the inputs are incorrect.

Ah, the C20XE, AKA KBA Cosworth!

A limit like that is common for "limp home" defaults where something is out of the expected parameters/limits. Exactly what ECU are you using - I've got an older MBE on mine and both stock and "chipped" ECUs - I'd loan them if you're running an OEM based box, but you're on the other side of the world... Still might be able to narrow things a little.

There are also some important detail differences between the earlier, dizzy engine, and the later coil-back - you can mix'n match most mechanical parts but things like the injectors, fuel rails/pressure regulators, TBS sender, etc are NOT interchangeable.

MIGWEB, a UK forum foe Vx owners, may be helpful - I used to be a member but drifted away from them as just got the XE engines in common, now.

Hi it’s had two different ECU’s on the car 1) was a DTA 2) is a Ecu master emu classic two different wiring looms and had a few maps on that the live tuner has tried we had it live tunes a few times and the tuner says everything looks good but it just won’t get above 3k had new bro crank sensor new crank pick up gear (the plate that bolts to the crank with the 60 -2 teeth on) so getting bit low on ideas

The car has got high impedance injectors in they have been tested and wired correctly to the Ecu we have a car with same engine on same injectors that runs nice unless these injectors are failing at higher rpm worth taking them out and checking I will check all bits that’s been aside thank you

Sorry, I haven't used either of those.

There are some basics, though -the engine needs three things - a spark at the right time that ignites the fuel-air mixture in the cylinder; the right fuel-air mixture in the cylinder; and the cylinder seal to compress the mixture and seal it against the combustion pressures.

There are some "old school" things to bear in mind and check, such as...

Is it running OK below that 3k point, and does it do so regardless of throttle position?

When it reaches the point, does it flater/misfire or does it have a sharp limit where it will rev right up to a point and just stop?

When it does so, what sort of engine/exhaust sounds does it make - is it a sharp 'crack', more of a muffled 'bang', or does it sound like lots of bangs in the exhaust manifold? The first would suggest a lean misfire - maybe a fuel shut of, the second is usually a rich condition, and the last usually an ignition cut off with the unbvurned fuel-air occassionally being ignited by the exhaust from other cylinders.

It would help if you could provide logs for when it's doing this for those that have the s/ware to read them, but there are some basic things you can do to try and narrow things down even without that.

You can check the ignition isn't cutting off by hooking up a timing light to each lead in turn - #1 & 4 should still be steady on their mark(s) and # 2 & 3 should be steady 180 degrees from the others - if the light flickers, or goes out, it would suggest an ignition cut, and if it holds steady it might suggest a fuel limitation. If it suddenly backs way, way right off (retards), it might suggest some sort of anti-lag is enabled, but as you've tried two different ECUs, that's darned unlikely. Two different units would also tend to rule out some other safety limit that has been enabled - unless it's different for each.

Something else that may help is to fit a fresh set of spark plugs, run the engine in the "limited"rpm range for a little bit and then pull and examine them - a shiny wet look, or carbonised look would suggest an electrical misfire/cut-off.

You can buy, or make (can't recall details, but should be easy to find), LED test lights that have male & female connectors that are fitted between the harness and the fuel injector(s) and these can show if the injector(s) are still powered during the limiting or not. On this, you DO have steady fuel pressure during this limiting point, don't you? Did you, or the 'tuners', monitor the AFR/lambda during this 'limiter' running - bearing in mind a rich misfire can read lean because of unused oxygen in the exhaust gasses. That last is a big reason why any halfway serious 'tuner' should be using a four/five/six gas analyser - they're getting very reasonably priced and they can tell a lot more about what's happening with the fuel burn and engine efficiency than a lambda ever could.

You mention it's been rebuilt several times - has this issue suddenly developed after a rebuild? If so, it may be a mechanical issue. For example, if the valve springs are weak, broken, and/or don't have the correct seat pressure - a very common problem when valves and seats are refaced/cut and they aren't correctly shimmed to correct for this - it's certainly possible the springs can't control the valve(s) and they're actually 'floating' and failing to seal.

High impedance injectors normally need a higher solinoid voltage and this is provided by an amplifier/driver or is sometimes enabled in the ECU - have you check that's the case? On a related subject, you have checked the power and grounds are sufficient for the power demands of the injectors, and coils, and tried giving them a shake in case it's down to an intermittent OC that only shows up when a resonant frequency is hit?

Sorry I can't offer constuctive help, but it'll either be something really simple you just never considered, or something so weird and unusual it never crossed any of our minds.

I deal a lot with DTA and ECU Master ECU's but the fact that the fault is the same regardless of the ECU and loom I'd say it's not likely in the tune itself.

Could you post the tune and a datalog from the car when it's 'limiting' and we'll hopefully be able to work it out?

I'm willing to check an ECU Master log and scope log as well.

Hi think we found the problem the we swapped the signal and sensor ground wires round and it will rev to 5000rpm now and sounds good just a bit rich now so we think it just need a tune and to see what is limiting it to 5k so looking promising thanks for all the help everyone

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