The V8 Owners Forum -

I've found a few threads where members have discussed an issue
with tuned 14CUX systems not keeping up under partial throttle.

Just wanted to see if this is my issue/what my options are.

Symptoms: Fresh built 4.8L stroker under 500mi break in period. Performs
great at ~1/4 throttle or more(almost too well!). But below that amount at low throttle levels(trying to obey speed limits) and taking off it can be quite 'jerky' and a pain in the ass to drive. I originally thought that I was awful at driving/not use to the 3.55 gear/htob setup - but I rebleed the system and it helped a bit. However I still have issues taking off and especially in 2nd/3rd gear at slight throttle trying to 'cruise'.

I can't find a 14CUX tuner stateside and I'm wondering if 1. Is the 14CUx system the issue? 2. Is MS my best option?

The setup I'm running:
3.9L Block
Buick 300 crank, 215 rods, ford pistons; 10.5:1 cr ~4.8L displacement
Ported 4.0L heads w/ stock valve
Crower 20230 camshaft
RV8 Headers -> x-pipe -> straight pipes at the moment
14CUX system w/ a chip provided from a gent who had a 4.8 stroker
as well.

I'm a college student so limited on funds and would prefer to stay with
an EFI setup. Thank you for any advice!

I have a similar problem on my 3.9 but it is built with a fairly radical JE102 cam with loads of overlap.

I get around it by running in a lower gear than I would normally use to keep the revs above 2000 and the bucking bronco stops

Ian

Ian - I'm assuming you have a mostly street driven vehicle? I suppose I should have included that this setup is in a ~2000lb '79 MGB(Bit heavier than a Dax I'm sure!) I'm fairly confident I've solved the 'taking off' portion of learning how to drive - just driving to get around the low throttle 2nd/3rd gear part. I imagine I'll learn to live with it if I stay with the system if thats possible.

The poor low speed performance is due to many factors, but the primary is that you are using a plenum chamber with a cam with more overlap. This means you get a certain amount of exhaust gas bounced back into the plenum at low speed during the valve overlap period that fouls the clean intake air, leading to a poor burn. You can also add to this, if you are using a hot wire AFM, the low speed airflow measurement is poor as its the engine is not breathing well, so the signal to the ECU can be out, so it mis -fuels the engine. This is made a whole lot worse if you are running a catalyst fuel map, as the ECU then tries to compensate for the poor burn with lots of fuel trim. The first fix is to try and get the mixture richer at low speed, than at least part masks the issue. Some of the ECU remaps take this into account on catalyst fueling, or you can try adding more fuel with the CO trim on the side of the AFM if running the non cat map on the 14CUX. On the subject of mapping- a wrong fuel map will introduce shunting in its own right, as the basic engine load / fueling values may be wrong, so the ECU tries to compensate after the burn has taken place with fuel trim. There is some benefit with messing around with the ignition timing as well to try and improve the burn in the affected area. At least if you run an aftermarket ECU you can mess around with the mixture at will. If you dont have to worry about catalysts, then switch to the green tune resistor in the 14CUX loom, and have a play around with the mixture on the side of the AFM. Ultimately you need separate throttle bodies to prevent cross contamination in the first place if you want to do it properly- at a price!

Ive put some info here:

http://www.g33.co.uk/fuel_injection.htm

I suspect Land Rover would have dealt with such an issue like this:


But quite how you arrive at the dimensions of such a Helmholtz Resonator I don't know.
It would keep the MAF working properly.

Chris.

14 cux is great on a road car but is not designed to run anything other than a standard engine, i tried allsorts to resolve mine with numerous trips to mark adams but in the end i was told the airflow meter wasnt quick enough to respond the signals to the ecu, i now have opted for the omex 710 system which is awesome although a little pricey but the engine is far superior to how it was on a hotwire system.