My 3,9 hotwire cuts at 5200 rpm

BlesvikRacing · Post by **BlesvikRacing** » Sun Nov 19, 2006 9:34 pm

Why?
And how can I fix it?
It feels like the rpm limiter are to low.
This is my first Rover engine and have only one competition with it.

Post by **Coops** » Sun Nov 19, 2006 9:39 pm

what colour tune resistor are you using on the ecu, as i have been told these act like a rev limiter too some times,

BlesvikRacing · Post by **BlesvikRacing** » Sun Nov 19, 2006 10:20 pm

This is my tuneresistor:

I think its a 470ohm resistor.

But the engine had "cats" and lamda's before I put it in my rig.
The wiring loom did I get from a friend in england and its from a engine without cats and lamda's.
Do I have to reset the ECU?
Is that possible?

My ECU:

markmills2000uk · Post by **markmills2000uk** » Sat Nov 25, 2006 6:15 pm

thats a green wire tune resistor which is 470 ohms and for a car without cats and lambdas although you can fit lambdas if you want and the ecu will pick them up,
the ecu uses this resistor to choose which fuel map to use,all the maps are already in the ecu,if you wish to put it in an engine with cats and lambdas you will need a White wire 3900 Ohms tune resister
i dont know anything about the rev limiter though

GreenV8S · Post by **GreenV8S** » Sun Nov 26, 2006 1:46 pm

How accurate is your tacho? If it's misreading it may be the rev limiter is coming in at higher revs than you think, in which case it may be working correctly. 5600 rpm is the lowest standard rev limiter I've seen on a 14CUX and 6250 seems to be more common.

Is it the fuel or ignition that gets cut, or just the engine starts misfiring?

If it's the fuel, then either you're hitting the ECU rev limit or the ECU is losing the ignition feed at revs.

If it's the spark then perhaps the coil or ignition module are the wrong spec or starting to break down and you are getting a weak spark.

BlesvikRacing · Post by **BlesvikRacing** » Sun Nov 26, 2006 2:35 pm

I have a Autogauge tacho with memory but I will test it with my multimeter too.
Its the fuel that cuts, in neutral with full throttle its on-off-on-off.. and the tacho is steady so thats why I don't think its the ignition.
If its the ecu, do I need a new one or will a new chip from ex. Rpi fix it?

markmills2000uk · Post by **markmills2000uk** » Wed Nov 29, 2006 6:06 pm

could ne ur fuel pump is not man enough,just a guess,

an easy fix would be to have the fuel pump so the ecu doesnt controll it,just have an extra switch in the dash to turn it on and off,
im a bodger

GreenV8S · Post by **GreenV8S** » Wed Nov 29, 2006 9:24 pm

BlesvikRacing wrote:Its the fuel that cuts, in neutral with full throttle its on-off-on-off.

Are you checking the electrical signal at the injectors? That's the most reliable way to chek. With a NOID light connected you would normally see the light getting brighter and brighter as the load and revs increases, then suddenly switch off for half a second as the rev limiter engages.

The 'standard' rev limits seem to be set somewhere in the range 5600 rpm to 6250 rpm, but it's programable and no doubt some engines were outside that range. To change it you would need to change the chip. This means ten minutes with a soldering iron to remove the old PROM and insert a chip holder in its place, plus you have to buy the chip of course. I don't know many people with the skills to create the new chip for you, Mark Adams is one of the best known names among TVR specialists, I think he supplies chips to various people so perhaps that's where RPI would get them from.