Duff Stepper?

[Simon]

I put on a brand new carb assembly (FZX 1463 complete with new stepper and ORFCO, but no vac switch, just the stubs, so I had to use my old vac switch) to my '88 Maestro 1.6. I removed the stepper motor and put on new Viton O rings. It was quite hard to push the stepper motor back into the carb and I can still see a slight glimpse of the brass stepper motor shaft even though the stepper motor appears fully seated on the carb body with no gaps, and the screws are done up tight. I had to renew the vac switch pipes as they split on removal. Same goes for the float chamber vent hose. I also renewed the fuel supply pipe from pump to carb.

Started the car from cold and it wouldn't idle or run properly at all. Looked under the bonnet: aha! vac hose disconnected by accident. Started up again, much smoother but won't idle by itself...no problem, twiddle the settings a little...idles nicely now so let's warm it up and give it a tune up, which is what I did. Results - lovely constant 800rpm tickover with no hunting and very smooth acceleration, plenty of power. Some might ask what's the problem? Well, I decided to fix the gearchange linkage that kept popping off, so I fitted a new complete linkage which took about an hour, and I then decided to take the car for a test drive. To my horror I found it quite hard to start and the idling was a little reluctant for a minute or so, then it smoothed out. I decided to test the stepper motor by simulating a cold start then a hot one in the usual manner, but couldn't detect that it had moved at all. The little plunger refuses to move and has stayed at about 4mm protrusion from the end of the rubber boot. Admittedly I didn't initially set the fast idle speed when I first fitted the carb. Can these stepper motors be damaged by re-rubbering them, is the apparently tight fit an issue. My old carb's stepper motor was working because the idle speed was all over the place, sometimes up to nearly 2000 rpm and cold starts were always fine with a fast idle of about 1300 rpm. Could my new carb's stepper be a dud?

I've just gone out and tried another proper cold start...well it started but wouldn't idle at all although it would rev freely. I kept it revved up on the accelerator until about quarter warmed up whereupon it managed to idle, although switching on the lights reduced the idling speed to - wait for it - 350rpm!

Do you think that I have a big problem here?

(for info: Ign ECU: NNN1009; Fuel ECU AUU1275; temp gauge works fine, normal is just below half way, dashpot filled with 10W/40; ORFCO never connected; even though carb is "new", "85" is cast into the body and it appears to have a funny linkage with a cam shaped cable pulley but with an earlier style method of adjusting the throttle position with a screw instead of the bend-the-tag-with-pliers thingy. It appears to have been factory done that way too! :confused: :banghead:

[MaestroTurbo]

Putting new rubbers on the stepper motor shaft wont have damaged it although you should have used some WD40 on the seals to help ease it into the carb body, when you tighten the 3 screws up the stepper then nips up fine against the carb with no visible brass. I would remove it and refit it the seals are not damaged.

I have found the motors themselves to be quite robust, its often the electrics and sensors controlling it that cause problems

[G Force]

:o I decided to test the stepper motor by simulating a cold start then a hot one in the usual manner, but couldn't detect that it had moved at all. The little plunger refuses to move and has stayed at about 4mm protrusion from the end of the rubber boot. :

Hi simon, after you have removed and checked the stepper motor seating, just a couple of things that may help. Because there is nothing that retracts the plunger other than the throttle shutting, sometimes if the fast idle speed is set too low the screw that adjusts this speed does not touch the stepper motor pin so it always appears stuck out and looks as though it does not move. when you simulate a hot start you should be able to just push the pin back in with your finger.

I've just gone out and tried another proper cold start...well it started but wouldn't idle at all although it would rev freely. I kept it revved up on the accelerator until about quarter warmed up whereupon it managed to idle, although switching on the lights reduced the idling speed to - wait for it - 350rpm! :

This could happen if the fast idle speed is set too low, or the throttle switch is not closed. The engine should also be fully warmed up to get a reliable result.


"new", "85" is cast into the body and it appears to have a funny linkage with a cam shaped cable pulley but with an earlier style method of adjusting the throttle position with a screw instead of the bend-the-tag-with-pliers thingy. It appears to have been factory done that way too! :confused: :banghead:

This sounds like an early carb, the screw you mention is for setting the lost motion link, you should be able to move the throttle quadrant "cam shaped cable pulley" about 5mm before it actually moves the carb spindle. this is to ensure the throttle switch on the accelerator pedle opens before the throttle. If this setting is wrong or the throttle cable is too tight or slack it can effect the throttle jacking opertion. You should always check this before and after making carb adjustments.

If when you have seated the stepper motor and set the carb settings correctly and ensured everthing is working great as it should do cold and hot. There is a chance that you still have a problem starting from part warm like when you had after replacing the gear links. This was a known problem associated with the early S series maestro & monty carb and was fixed by using a special vacuum switch LZX 2292 and had a Z stamped on its body.

Cheers Gary :)

[Simon]

Thank you both for your swift replies. I was just a bit miffed that it wouldn't work properly initially. What I did first thing this morning was to test the stepper motor circuit first by plugging in my old stepper. It worked as it should on simulated cold and hot starts. I learned that the plunger itself doesn't retract by itself...silly me, I thought it did! Well that was a result because then I could adjust the fast idle screw which, quite predictably was a horrendously long way out. I ensured that lost motion and stepper push rod clearances were within the tolerances and then proceeded to start the car from stone cold. Result: about 1650 rpm fast idle! (but a lovely smooth clean drive-away from cold) after warming it up for about 5 miles up and down the bypass I commenced tuning and now have approx 1200 rpm fast idle and 800-ish idling speed! Car is so much smoother although I'd suggest that it is running a touch lean. I did recall putting a little WD40 over the spindle/O rings to help ease them into position. The problem is, you see, I'm cursed with a dreadful affliction called "Mechanical Sympathy". At least I've furthered my knowledge about stepper motors etc - something that I'd not encountered much before. I should have replaced the carb, or at least the stepper motor seals years ago! I have an LZX 2292 vac switch, no markings on it but it is meant to be "Yellow Spot" meaning the latest spec applicable to the FZX 1463 carb.

Once again, thanks for the good advice - it is much appreciated! :spanner: :thumbup: :)

[G Force]

Hi Simon I just logged on to edit my previous post as I quoted you the wrong Vac switch. The modified switch was indeed the one you have LZX 2292 only thing was it should of had a black spot and Z stamped under it?. This was introduced to cure what was dubbed as paper shop syndrome at the time. What used to happen was the car would start fine then drive down the road say a mile, then if it was stopped for say 5 or 10 mins like if you called at the shop to buy a paper, when you tried to restart the engine it would flood. The problem was that the coolant around the temp sensor would cool faster than the cylinder head, the ecu would respond to this by adding additional choke but in a disproportionate ammount to what was needed by the engine. They got around this by bleeding more air into the choke with the modified vacuum switch. sos for the initial error :hide: Ill go now and correct it :o

Cheers Gary :)

[Simon]

Funny, that's exactly the name I've heard it quoted before! I've had that happen to me a couple of times before, once whilst getting a newspaper! and have got over the inability to start by undoing the damper from the carb and lifting it sharply upwards so as to make the piston rise up then fall. The car has always started afterwards, thankfully.

I can report, 2 or so days later that the car is basically transformed, it starts immediately well and drives smoothly under all conditions although I'll need to set it a touch richer than I've got it currently and I've put a little too much slack in the accelerator linkage, which is easily sorted.

[G Force]

I can report, 2 or so days later that the car is basically transformed, it starts immediately well and drives smoothly under all conditions although I'll need to set it a touch richer than I've got it currently and I've put a little too much slack in the accelerator linkage, which is easily sorted.

Excellent, job well done! :)