14cux stepper shows zero in RG

[ricey30]

Hi Guys

I normally lurk on the MGexp forum for engine swaps, but am seeking specific 3.9 efi advice which I'm hoping I can ask you guys about?

Hit a snag with the 3.9v8 whereby im trying to sort out the idle and I cannot get the idle to increase or decrease with RG soft ware. When I step it out using the software the green bar increase but there is no increase in idle RPM. Same if I decrease it. Once the cars warm my stepper motor says zero, MAF 28% direct, throttle 4%, MAF trim 1.39v.

when starting from cold it will fire straight away, but bounces around from nearly stalling to 900rpm then if I can feather it long enough it will settle down.

If I rev the car the stepper motor percentage increases on RG whcih I guess is to stop it stalling.

am I right in guessing that the stepper motor isn't doing anything at all?

Smells very rich on tick over.

I have a new ECU with one of the tune files from blitzracing which I want to fit but don't see the point just yet until this is sorted.

Its non cat by the way.

Edited by ricey30 on Tuesday 30th November 19:54

[blaze_away]

Before jumping to any premature diagnosis start off from a known correct position.

Go set the base idle properly, details over on the act products web site and or RPI website.

This involves running engine up to temperature, blocking off the hose to the stepper motor and setting the "base idle".

Then remove the stepper and thoroughly clean it and its housing.

[Steve_D]

blaze_away said:

............Then remove the stepper and thoroughly clean it and its housing.

OP
Worth knowing that you can use RG to help with cleaning the stepper.
Remove the stepper and plug it back into the loom. Use RG to tell the stepper to close. This drives the plunger until it comes right out of the housing along with its spring. With it in bits you can now get it really clean. To put it back together push the plunger and spring into the housing then tell RG to open the stepper. This should pull the plunger back into the body.

Steve

Don't think I need to say if the plunger does not move then its FUBAR.

[ricey30]

Thanks Steve I’ll work through that this week. I’m pretty sure I dint have the base idle turned low enough to start with.

Thanks

[spitfire4v8]

It's possible you have a fault because RG should power the stepper in and out and you should see a change in revs.. have you actually held the stepper in your hand and used RG to move it, and does it indeed move or not? , but even if everything was ok your stepper position would still be zero in that screenshot because the ecu is trying to target a super low idle speed, which the engine is already above, so the ecu will always want to close the stepper more.

If the stepper DOES move with RG then forget about the internet guides for setting base idle for a moment .. wind the base idle screw in and see if you can get the revs low enough that the ecu tries to open the stepper to achieve 660rpm target speed.

If the stepper does NOT move in RG can you at least feel the stepper trying to reset on ignition key-off ?

[ricey30]

Well I had a fiddle and get the stepper to move using RG and ignition so that’s all good.

Don’t ask me how but I also discovered a vacuum port on the stepper motor housing which was wide open to the atmosphere. I presume it should have the vac hose off the fuel diaphragm attached to it! This is currently plumbed to the plenum chamber baseplate?

Clearly this would have been providing plenty of air hence the lack of idle etc 🙄

Stopped today but tomorrow I’ll connect fuel diaphragm vac to this port and block off the plenum port.

I’ll report back……


Thanks all
Phil

[blaze_away]

ricey30 said:

Well I had a fiddle and get the stepper to move using RG and ignition so that’s all good.

Don’t ask me how but I also discovered a vacuum port on the stepper motor housing which was wide open to the atmosphere. I presume it should have the vac hose off the fuel diaphragm attached to it! This is currently plumbed to the plenum chamber baseplate?

Clearly this would have been providing plenty of air hence the lack of idle etc ??

Stopped today but tomorrow I’ll connect fuel diaphragm vac to this port and block off the plenum port.

I’ll report back……


Thanks all
Phil

99.999% you've found the issue.

That vac pipe should connect from Stepper Motor housing to the Fuel Pressure Regulator (helps keep fuel pressure at injectors at a constant delta from manifold pressue).

Some stepper motor housings have 2 vacuum points (mine has)
1. to the fuel pressure regulator
2. to the distributor vac advance (this is to give full manifold vac to distributor vs connection on top of the plenum, which is called ported vac advance)

By preference use Full manifold vacuum for everyday use, switch to ported for MoT) Ported supposedly reduces emissions at idle) Full vacuum will give you better (smoother) idle performance.

Edited by blaze_away on Wednesday 1st December 19:11

[ricey30]

Feel a bit of a tit cant believe I missed that port. Ive been driving it quite happy thinking it was just a bit lumpy and rich at tick over

Be interesting to see difference when I finish off the vac swap.

Probably explains A the stench at idle and also I felt it very ON/OFF when hitting the accelerator, I just assumed having never had injection on the car before that this was normal....

Cheers
Phil

[blaze_away]

We have all got to learn some how. Welcome to the world of 14CUX

[ricey30]

Right

after much fiddling got a new stepper motor from Rimmers as my old one just didn’t seem to move except intermittently.

Fitted it and what a difference. On start up it goes to 1150 when cold and works itself down which is way better.

I’ve taken the fuel diaphragm vac to the vac by the stepper motor abd blocked off the vac port at the plenum base.

Now it stays very stable on idle so I put the R3652 chip in to see what it did and it’s much better with target idle of 800.

When revved the stepper catches it so doesn’t cut out. Haven’t driven it yet or set base idle properly but so far so good with the new stepper.

Next question is it worth my while changing the dizzy advance the the manifold vac? Cars over 40 so no issue with mot?

And finally I could burn another TVR chip any suggestions? ( I do have a MC1 cam in it from the carburettor days, pending stage 2 heads)

Thank you all for your advise saved me a lot of fancying about

Phil

[Belle427]

I noticed a smoother running car when switching over to the full manifold vacuum, there is a lengthy thread on here about it somewhere.
May not work for everyone.
There is some very good info here regarding the 14cux.
http://www.remap-14cux.uk/

[ricey30]

Guys

Swapped to full manifold vacuum, set it at 10 degrees btdc with vac disconnected, went for a drive what a difference! So much smoother and the R3652 chip keeps it at 800rpm with nice 25 on stepper and 1.4v on the maf .

Very happy thank you all for the advice and I busy reading all the other threads abs now actually understand what does what.

Brilliant help cheers

Phil

[blaze_away]

ricey30 said:

Guys

Swapped to full manifold vacuum, set it at 10 degrees btdc with vac disconnected, went for a drive what a difference! So much smoother and the R3652 chip keeps it at 800rpm with nice 25 on stepper and 1.4v on the maf .

Very happy thank you all for the advice and I busy reading all the other threads abs now actually understand what does what.

Brilliant help cheers

Phil

Nice one Phil. I'm 20 yrs into Chim and thus RV8 14CUX ownership and learnt a massive amount from the very kind and knowledgeable folk on here, enjoy the new found silky smoothness.

[Belle427]

When everything is well with the 14cux it’s pretty good really, I only really decided to go aftermarket with Megasquirt on my old car due to problems with the ignition side of things.
If quality ignition components were still available I wouldn’t have bothered.