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MG MGB GT V8 Factory Originals Technical - EFI Stepper motor question
|I suspect that the stepper motor on my EFI is playing up. After running along at high speed for 20 minutes or so, and I take it out of gear (ie. stopped at traffic lights), the motor doesn't idle, it stalls. Once I restart, not a problem.It doesn't do this every time, just often enough to be a nuciance. |
From what I understand the stepper motor controls the idleing by opening and shutting and either leaning or riching the mixure by 'short circuiting' the volume of air getting to the cylinders. I suspect that the stepper motor is slow at activating after periods of inactivity. Has anyone else had this problem?. Any ideas? The obvious solution is to put n a new stepper motor, however they cost more than $300; an expensive experiment!
|Peter have you checked idle settings?? O2's etc?? is she running different other than the stalling?? EFI is a wonderfull invention with regards to efficiency, smoother running, better performance, but can be tricky to diagnose problems with. After it stalls will it start right up? Does it chug or lope before dying? I bet If you could get actual A/F readings during all running and then when it stalls you could narrow things down quite a bit. Dirty sensors, MAF, TPS, O2's among others could all do this type of thing.|
Further to Larry's wise words - make sure the valve is clean and that the speed sensor input is intact. Stall after speed is a classic speed sensor symptom.
|Stateside, Stepper motors are about $30.00 and I'm sure shipping would be a far cry less then $270.00 Probably closer to $20 or $30. A lot of GM vehicles use them. (1987 buick regal with 3.8L V6) Maybe you could contact an online auto parts store state side and get a few of them shipped to you?|
My car used to be horrible about doing that. I found most of the time my airflow meter had disconnected and plugging that in was a great remedy. I don't have a speed sensor, and I don't think the car much really cares it's not there.
|The stepper valve should be set up to increase the idle slightly above the base idle which is set on the throttle body, ie, bring up the idle from ~650rpm to ~850rpm. Therefore the car should be capable of idling with the stepper valve closed. There does seem to be a slight delay before the CU reads the O2 sensors and adjusts to the correct idle. I'm also running without a speed sensor.|
Like Larry says, lots of things to check but you should be able to get the stepper valve closed (procedure is somewhere in the Rover manual) and the car should idle with it disconnected.
IAC valve can stop working, however if I were you I would check the TPS (throttle position sensor) O2 sensor and CLEAN out the passage where the IAC works. Unscrew the IAC and inject some brake cleaning fluid (carbon tetrachlroide) in the air passage or remove the housing and really clean it. The IAC stepper motors are on a lot of cars these days, maybe one from a wrecking yard car that looks newer than the one you have would lead you in the right direction. This passage will sometimes get plugged and negate the operation of the IAC. I had this type of idling problem and changed all of the above and cleaned the IAC passage, started it up and within a few miles of regular driving the computer relearned my driving parameters and now it runs like new. FWIW Alan
A good Fuel injection book will shed more light on the subject.
|Not too sure where my reply went, I'' try again.|
Larry, the motor runs like a dream, except for this one difficulty. Sometimes the motor will idle normaly, others the rev's will just smoothly decrease to zero and stall. Sometimes the rev's will drop to about 50 then fire up to about 850 then after a short while drop back to 750, which seems to correspond to Edds remarks. Once restarted there is no problem at all, until the next fairly exiting go on the freeway.
Roger, like some of the others I don't have a speed sensor and initially had no problem. But perhaps you're right and under certain operating conditions the motor needs to be remined that the car isn't stationary. This problem has only developed since the weather turned colder, which may also be just a coinsidence.
Alan, I'll try clean as you suggest, as the first move since it's easiest and cheapest.
Justin, from your remarks I would guess that the local GM products are likely to be using the same component, but at a very different price, I check them out, thanks for the tip.
|man that sounds fish... I am still thinking it is one of the other sensors..|
that sounds like a classic MAF sysem adjusting down and going to far. Case in point, when I started the motor in my 91LX that had been wrecked and sat 1+yr. the motor revved up to 3k, then every 1-2seconds would dropp down by 500rpm till it settled just under 1000. That was the car relearning it's A/F tables etc..
It sounds like your motor is doing that but not stopping at normal idle? that woud lead me to TPS, MAF anf O2's 1st off. If you are using a K&N filter go for the MAF 1st. Believe it or not there have beeen problems with K&N's and MAF's. the oil they are coated with can leave the filter and get on the sensor which will make it act up. There is a wide range of techniques people recommend and not recommend for cleaning them. the sensors are VERY sinsitive inside, you would not want to touch the little loop. but brake cleaner had been widely recommended. Take it off the car and flush it good. LEt it air out and give it a try.. Also check all connectors to be on and tight.
Best of luck!!
You could be onto something with the filter. It's not a K&N but something that looks very similiar.
wrt this cleaning the MAF, somthing I've not done before. Do you actually run/pour brake cleaner through the side channel where the wire is?, wouldn't that distroy any electronics?
I notice that there is an adjustment screw on the side of the MAF (the protective cap has been removed/pierced) . I would assume this would be a variable resistor between the two wires.
|This is a common problem on Ford Mustangs retrofitted with K&N oiled filters. Here's a link that shows how they solve the problem.|
I used their method on my 5L Ford in a Mustang and it was simply amazing how much better it ran after cleaning the MAF.
While I used the Q-tip technique, elemets in other sensors may not be as robust. A mechanic told me you have to be careful if you use a solvent on them too, as some of the wires have a thin coating which can dissoved by agrressive chemicals shifting the output characteristics.
Here is a link that also might be useful for troubleshooting your system.
|You don't pour into the electronics.|
Rmove the MAFom the car. Find the port that it uses to get it's air readings. you sould see a loop or thin metal element hanging in that port. Take brake cleaner and flush that port out. I would not stick the tip of the cleaner into the port or anything, but give it a good flush and then let it air out. I was told not to use the q tip method, because as mentioned these things are super fragile. Your not cleraning the circut board, just that element in the port.
I have not heard of the issue from other filters, but I have heard it from high mileage cars also. Any dirt, or oil on that element will throw it's reading right out the window. So if it sat in a box or just in garage for a bit during build up, it could have gotten contaminatied.
Did you clean the MAF on your rover motor when you had it? If so, what was the procedure you used?
p.s. Got that dune buggy with the cadilac northstar up and running yet?
When I first got the MAF I blew brake cleaner through it, but I didn't try and run it first so I would have a back-to-back comparison.
Sounds like Edd has been playing around with it - perhaps he's tried to clean it. Edd?
The Northstar is on ebay - OBDII electronics is too fussy and nobody hacks the Cadillac that I can find. Ordered an LS1 instead. Chassis will be here in August, so I've got a while. Built the electronics for my brother's car w/'93 Northstar and went to the dunes 2 weeks ago - lots of fun.
Different topic - saw a Sunbeam Tiger at the drag strip Friday. 302 Ford, Ford rearend with traction bars. Laid down a 10.6 sec 1/4 mile time. Had NOS and some narrow slicks. Said with a 275 shot of NOS and cooler weather he thought he could get it under 10. If I don't stop thinking about this, I'll be building a 5L Ford MGB soon.
|I wondered how long it would be till you got another B. Can't really seem to get them out of the blood too easily. =)|
|he probably had some of the 8" wide import slicks, they mount on 13" wheels which means lots of sidewall flex and lots of bite.|
HE also must have had allot of power out of the 302. Any word on what his trap speeds were? he must have installed a full cage also?? I am looking forward to and dreading the track this year. I know will run into 12's with the car and they will kick me out. I need to design a cage or roll bar to protect me and still fit under the hardtop. A Normal one will not work as it occupies the same space as my head.
|I just confered with a local EFI mustang guy, he said sounds like IAC (Idle Air Control) which is probably what your stepper is. SOO, I would say clean everything up, see if it helps, if not get one of the stateside $30 units and check that out..|
Also try blocking off that valve and get the car to idle with it closed just to be doubly sure. If you TB is set to low, then the only way the car may run is with the stepper open.. that is not what you want, and would cause this intermitten problem with the ECU did not sense the problem soon enough the motor would stall as described...
|The Sunbeam Tiger didn't have a cage, but he was racing with a helmet on. They were not 13" slicks, but I'm not sure what size they were. I'm pretty green in the drag race game, so I didn't think to ask what his trap speeds were. It seemed he wasn't all that fast off the line, but acceleration mid track was excellent. He was from New Mexico somewhere I'd never heard of.|
To set the base idle on the Rover, the method I recall is this: Turn the ignition on without starting the motor, unplug the stepper motor, then turn off the ignition and reconnect the stepper motor. Repeat this process 3-4 times to make sure the stepper motor valve is against the seat in the plenum (helps to have cleaned all the gunk out of the valve and seat before you start with this) You do hear the stepper motor cycle with a series of clicks each time as you turn on the ignition, right? Leave the stepper motor disconnected, then screw out the idle air bleed screw about 3 turns and start the motor. Adjust the idle with the an allen wrench on the butterfly stop (You may have to turn the screw around and insert it from the top you you can put an allen wrench on it from the top of the manifold while you hold the butterfly open. Since the screw is under the stop you may have to itterate on it several times before it idles where you want it) When you get the RPM close with the butterfly stop, do the final RPM tuning with the air bleed screw to achieve aroun 800-850 RPM. Reconnect the stepper motor, and you should be good to go.
The stepper motor has limited authority to control RPM. What you're trying to do is establish a 'base' speed around which the stepper motor will control idle-up conditions.
|HRMM, that is REALLY surprising. convertibles are not allowed to run any faster than 13.99 technically (IHRA & NHRA) without a full cage. But It being that fast is awesome. He REALLY must have something done to that motor. I had around 280hp last year and could only muster 13.8 @102 due to traction..|
I hope to run solidly into the 12's this year maybe even be at the 11/12 border before I get kicked off heh
|Many thanks Phil ,Larry and Edd, I'll give this a go next time I'm off shift. Some v'good links. Armed with this info' I should be able to solve the problem.|
This thread was discussed between 15/05/2003 and 24/05/2003
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