Rev limiter kicked in early - weird

[thegman]

Very weird thing happened to me on Saturday.

Car had been driving fine for about an hour on the motorway. Came off onto A-roads, gave it beans and then at about 5000rpm in 3rd the car lurched as the engine just stopped firing, then rev'd again and the same thing happened. The ignition just stopped but the car did not stall or lose secondary power.

I have never hit the rev limiter in my Chim before - always change before 6250, so I don't know what it feels like - but this felt just like the rev limiter does in other cars. I tried several times in different gears and it just bounced each time.

Then I stopped trying and carried on driving with no other problems - until I pulled into a roundabout and the engine kept dropping revs and nearly stalling.

Finally when I got in the car on Sunday, let her idle warming up - and she just stalled. Restarted (didn't want to - had to pump the throttle a bit - seemed like it was flooded?) and then no problems. On the drive home - muchos beans... but no problems.....

Now before anybody starts - I have recently(ish) replaced many ignition components, which solved another issue I was having with a missfire under load. I cleaned the stepper motor and can verify it definately works - but maybe it needs another clean?

Any ideas? These problems are so infuriating.

[scorcher]

I had the same thing with my Griff.Mine would nosedive at about 4000 rpm as if the limiter had cut in. Only ever happened once.I'd also been through the process of sorting a misfire and had replaced various ignition bits and pieces.I disconnected the ECU for a few minutes and every thing has been fine ever since.

[blitzracing]

Its possible its not running the TVR fuel map for some reason and has gone into the default map. I cant honestly say if the same overall RPM limit occurs for each map or if part of each map data is the limit however. The stock Range Rover map is as low as 5200 rpm. Id agree and ECU reset sound good, and if that does not clear it, borrow a fault code reader.

Mark

[banjolucknicker]

I'm certainly no expert but could it be the air flow meter? I had a Alfa that exhibited similar traits where it felt as though it was cutting out when 'pressing on'.

Easiest way to tell is swap an AFM from a car that's working and see if the problem repeats itself

Hope you get it fixed soon, what ever the issue...

[thegman]

just to be clear - the problem has 'fixed itself' in typical tvr fashion. but as you can imagine it is pretty scary when you are overtaking and suddenly loose power.

i recently replaced the afm after my last misfiring problem, and it seems ok. but tbh i probably need to take it to have it checked out properly. i dont have a multimeter.

who could i take it to that would test the afm, fuelling etc to see that it was optimum? would somebody like m.a be able to do this?

[MikeTVR]

Ensure that the AFM connections are good. I've had similar problems over the last year or so which seems to be resolved now that I've tweeked the connector. Ideally it should be changed out but I'm finding it difficult to find a replacement. If you look into the cable connector the two spring fingers on each connection should pretty well touch.
I've established that no fault code is issued from the ECU if the connection is lost momentarily so a fault code reader is not reliable for this fault.
Removing the connector whilst the engine is running has the effect of an immediate cut on the engine - no half measures.

Mike

[blitzracing]

thegman said:

who could i take it to that would test the afm, fuelling etc to see that it was optimum? would somebody like m.a be able to do this?

Fuelling is automatically set by the Lambda probes, and these will keep the fuelling optimum so there no AFM adjustments to be made. If however the engine drops out of its lambda range for a period (not the odd glitch) the ECU will go into fault mode. Its not that sensitive however, and some AFM's run better than others still without going into fault. I think they go out of tolerance because dirt / oil and bits of air cleaner actually bake onto the hot wire (Its HOT !!), changing its heating / cooling characteristics. A good blast of "Easy start" through the hot wire port (When the engines off !!) can remove some dirt but I had to physically scrape debris off one I looked at (having stripped the AFM to bits first.) I think the only way to be sure the AFM voltages are factory spec' is to get a recon' one. The units I have seen so far have shown quite wide voltage variations, and they have internal "trim" resistors to calibrate the output, against a given airflow. Bench testing is not that easy, having strapped a 2kw garden vacuum cleaner on one to try and replicate an engine under full load / rpm. Still did not get close to what the engine draws !!

An AFM out of tolerance wont produce the sudden cutting out problems, although bad connections could.

Mark