shudder/rev drop off

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suburban_ennui
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shudder/rev drop off

Post by suburban_ennui » Mon Sep 03, 2007 5:37 pm

Coming home last night on the motorway, I had a couple of weird shudders ... kind of like I was "bunny hopping". They stopped before I could work out what was going on. Tonight, driving home, I had the same problem. Everything appears to be running fine, but then, for a brief second the revs drop away suddenly, the car shudders, and then comes back to normal. It's an intermittent problem, and has never happened before yesterday, although it happened about three times on the 10 minute drive home. Speed doesn't seem to be an issue - it happened twice on the motorway, and once doing between 40 - 50km/h. Any advice appreciated before I go check my car in at the garage.

(Oh, and it's a 1990 V Spec, manual, 1600cc)

suburban_ennui
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Post by suburban_ennui » Mon Sep 03, 2007 6:24 pm

oh, and I had the cambelt replaced about five months back. if that makes any difference.

SLYDIT
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Post by SLYDIT » Mon Sep 03, 2007 7:18 pm

THINGS TO CHECK ARE....

Check the ECU in the passengers footwell to make sure it isnt full of water... :)

Disconnect the battery and then remove the earth connections from the engine and chassis in the engine bay and clean with some fine emery..this includes the funny plug with all the black wires in it thats beneath the wiper motor..

Check the plugs that go to the coil packs there has been some cases of the wiring in the loom to the coils getting broken with engine movement and creating an intermittant contact.

Changed the leads/sparkplugs lately??

Also a few guys have experienced problems with the air flow meter, Basically the electrical wiper inside the afm gets a bad contact at a certain point causing the car to do funny things at a set airflow or speed, causing it to "hiccup" when driving..Removing the black cover on the afm and cleaning with contact cleaner or a fiberglass pen seems to fix this..
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zorruno
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shudder/rev drop off

Post by zorruno » Mon Sep 03, 2007 7:31 pm

suburban_ennui said on 09/03/2007 05:37 PM:
Coming home last night on the motorway, I had a couple of weird shudders ... kind of like I was "bunny hopping".
Most likely your Plug (HT) Leads need replacing. Should put something
in the FAQ really...

cheers
Last edited by zorruno on Tue Sep 04, 2007 9:00 am, edited 1 time in total.
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suburban_ennui
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Post by suburban_ennui » Mon Sep 03, 2007 9:19 pm

Cheers ... sadly ... almost none of that makes sense to me. ECU? Earth connectors in the engine? I guess I'd better head to a garage. Thanks anyway.

poison
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Post by poison » Mon Sep 03, 2007 11:39 pm

Is your car BRG (British Racing Green)? It could then be that it was so ashamed when passing near another MX5. ... :lol:

But in a more useful vein...

HT leads are just the spark plug leads, these can break down over time and cause various smooth running problems. At one end of these is the engine and spark plugs and at the other end the coil packs, which make the spark).

ECU - is the computer, and sits under the passengers foot well, especially placed to fill up with water if you leave the roof down/window open when facing downhill (when raining) so this area immediately fill with water, and we all know… water and computers... oh dear!

AFM or Air Flow Meter - is the black box on the air intake after the filter, this measures the air into the engine so the ECU can decide how much fuel to put in.

Good luck with the garage though. Intermittent problems are often the hardest to find. What city are you in? I’m sure some members can recommend a workshop who is MX5 savvy.
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DBM58
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shudder/rev drop off

Post by DBM58 » Tue Sep 04, 2007 7:43 am

I had a look through the "Mazda Miata Enthusiasts Shop Manual" last night and found that there is a lot more detail and explanation than there is in the Haynes manual. It has easy to follow guides that expand on the suggestions already made. You are welcome to borrow it if you like. I have fixed a couple of things using its instructions and as well as the repair, it gave me more confidence to try more before taking my car to a garage.
Last edited by DBM58 on Tue Sep 04, 2007 7:57 pm, edited 1 time in total.
David

suburban_ennui
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Post by suburban_ennui » Tue Sep 04, 2007 8:15 am

David - thanks. Is this a book one can go out an buy? It'd probably be a good thing to get because that Haynes model normally poses more questions than it answers for someone only vaguely mechanical like myself.

Anyway ... after reading the threads last night it occurred to me that on Sunday afternoon I was fiddling with the earth switch (?) in the engine bay. It'd been packed down in the "down" position and had some tape over it. I took the tape off, cleaned the switch with some CRC and left it, not really understanding why it'd been stuck down. However, this morning I noted that, if I popped the bonnet with the engine running, the engine would immediately cut off. So I assume this is the problem ... road vibrations were probably jiggling it and causing the engine to cut out. I've packed the switch down with cardboard again, and haven't had a repeat of the engine-rev-drop-off issue.

So -
a) what exactly is the point of a switch which cuts off the engine when you pop the lid, or
b) if that's not the point, do I just need to replace the switch.
c) or something else.

Sorry to bother you all ... but thanks for the good advice so far. At least I (vaguely) know what I'm dealing with now.

DBM58
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shudder/rev drop off

Post by DBM58 » Tue Sep 04, 2007 8:26 am

I bought my copy of the book from Technical Books in Newmarket. I took the version for the 1,6 liter but ther is also one for the 1.8 liter. I think that both are for the NA series.
Last edited by DBM58 on Tue Sep 04, 2007 7:58 pm, edited 1 time in total.
David

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Post by zorruno » Tue Sep 04, 2007 9:21 am

suburban_ennui wrote:Anyway ... after reading the threads last night it occurred to me that on Sunday afternoon I was fiddling with the earth switch (?) in the engine bay. ...if I popped the bonnet with the engine running, the engine would immediately cut off.
There is no such switch as standard. Can you submit a photo? I'd guess you were looking at an aftermarket pin switch for an alarm or something similar. As to why it would cut the engine off when operating, I'm not sure - the only thing I can think of is if it was part of an autostart circuit, but it still should only stop the engine if the engine was started by remote.
suburban_ennui wrote:So I assume this is the problem ... road vibrations were probably jiggling it and causing the engine to cut out. I've packed the switch down with cardboard again, and haven't had a repeat of the engine-rev-drop-off issue.
I honestly think this is coincidence. The HT lead problem is by far the most common cause of the symptoms you described, and will be very much intermittent. When it first happened to me, I didn't understand the issue, but replacing the leads fixed it immediately. Just ask for a set of Plug Leads for your model from Mazda, (or Repco/supercheap) and you should easily see where they go and how to replace them. If you get stuck, post.
(z)

suburban_ennui
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Post by suburban_ennui » Tue Sep 04, 2007 9:28 am

zorruno wrote:There is no such switch as standard. Can you submit a photo? I'd guess you were looking at an aftermarket pin switch for an alarm or something similar. As to why it would cut the engine off when operating, I'm not sure - the only thing I can think of is if it was part of an autostart circuit, but it still should only stop the engine if the engine was started by remote.
I'm pretty sure that the switch has something to do with the alarm ... which I always assumed was a factory-fitted keyless entry/alarm/immobilizer system. (Maybe it's not factory-fitted.) Anyway, I'll try to post a photo later today - looking in the engine from the front, the switch is on the left hand side, just up from the pop-up headlight. As mentioned previously, if the engin is running and I pop the bonnet, it opens the switch and kills the engine. Hence it being taped down. It just seems like a weird coincidence that this problem occurred almost immediately after I took off the tape that was holding the switch down.

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shudder/rev drop off

Post by joanie » Tue Sep 04, 2007 12:53 pm

There is a very good cd manual available from EBay. It has the workshop manual for models 1990 - 2002 plus the Haynes and many other interesting titbits too :-)
Cheers Joan H
http://motors.search.ebay.com/ebaymotor ... =&from=R43

suburban_ennui
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Post by suburban_ennui » Tue Sep 04, 2007 1:12 pm

and here's the mystery swith if anyone can shed any light

Image

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Post by Growler » Tue Sep 04, 2007 5:21 pm

That is a switch to an alarm - If someone opens the bonnet they can't start the car etc.
If you aren't using it you can either "disable" it (I assume by connecting the two wires tha go to the base of it together) or speak to a friendly automotive sparky to sort it out. However your key in the ignition should override this switch....unless you have recently stolen it yourself!!!

Growler.

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Post by zorruno » Tue Sep 04, 2007 5:56 pm

suburban_ennui wrote:It just seems like a weird coincidence that this problem occurred almost immediately after I took off the tape that was holding the switch down.
I didn't realise sorry this was done before you had the problems - I thought that you were playing with the switch after the problems (and when looking in the engine bay). Therefore it is quite possible I suppose that if the switch base was bumping some bare metal the engine could cut out briefly. Also those switches can have problems with water tracking down them causing a connection.
Growler wrote:That is a switch to an alarm - If someone opens the bonnet they can't start the car etc.
If you aren't using it you can either "disable" it (I assume by connecting the two wires tha go to the base of it together) or speak to a friendly automotive sparky to sort it out. However your key in the ignition should override this switch....
You mean people would actually wire such a thing? I'd vote for the sparky if you are not electrically adept yourself. Sounds like a dodgy thing to have installed. Going 100kms around corners and having your engine cut out because of a dodgelly (sp? word?) wired 'security' device is probably not a good thing.

suburban_ennui, you might want to do a quick trace on where that wire goes. There will only be one wire, and a quick fix would be to cut the wire, and wrap the end with heat shrink, or insulation tape. I wouldn't call it a permanent fix though - if the tape cane off and the wire touched grounded metal, the engine will stop.
Growler wrote:....unless you have recently stolen it yourself!!!
Ha. good ploy.... hey, I've locked my keys in my MX5 - anyone know how to get in easily via the soft top... and disable the factory alarm so I don't wake the neighbours? Oh yea, I can only do this at 2am... and any tips for better visibility when driving with a balaclava?

By the way suburban_ennui - you must be an artist :)
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suburban_ennui
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Post by suburban_ennui » Tue Sep 04, 2007 6:32 pm

zorruno wrote:By the way suburban_ennui - you must be an artist :)
Not sure if that's scarcasm or not :) - if you're referring to the quickie photoshop job above - I spend about 50 hours a week in front of a Mac using Flash and Photoshop.

As you surmised, the fiddling with the switch happened *just before* the problems started. So I'm gathering that's the issue. I think I might just work out if I find where the switch plugs into, and then just disconnect. Seems fairly pointless.

Cheers for the advice everyone ...

poison
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Post by poison » Tue Sep 04, 2007 6:51 pm

No he's not into sarcasm, that's more my field of expertise.

The switch is for an alarm and when the bonnet is opened it sends an earth back to the alarm. If it not set-up correctly then it may make contact when the bonnet is closed and sends an earth back to the alarm which in turn will kill the engine. This may well be intermittent and given it was taped down sounds like the problem.

So you have solved your problem, no need to blow big bucks at a garage, you may still want to go to an alarm centre to have them re-adjust the switch. It's easy to do, loosen the nut at the botton and reach below and turn them so the switch moves up. Check the clearance now and again so the bonnet can still close safely. If you live on the Shore I can do it for you.
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suburban_ennui
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Post by suburban_ennui » Tue Sep 04, 2007 9:18 pm

poison wrote:So you have solved your problem, no need to blow big bucks at a garage, you may still want to go to an alarm centre to have them re-adjust the switch. It's easy to do, loosen the nut at the botton and reach below and turn them so the switch moves up. Check the clearance now and again so the bonnet can still close safely. If you live on the Shore I can do it for you.
Right then. Cheers. One (hopefully) final question - presumably I can take this switch out (if I can follow the lead back to where it's plugged in) and it won't effect the alarm? My alarm has been giving me a lot of grief the last few months ... going off intermitantly, and taking the tape off this switch was initially an attempt to solve the alarm problem. (Alas - it just created a car-stops-working-altogether problem.)

Any idea if I can basically disable the alarm (because I'm not too worried about being ripped off and I never leave anything valuable in the car) but still keep the remote locking? Or is it a take it or leave it deal with these things?

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Post by SLYDIT » Thu Sep 06, 2007 3:00 pm

if want the switch to stop "working" then simply pull the wire off the bottom of it.It will just be a spade terminal plug...tape up the wire/terminal with some electrical tape so it wont ground to the chassis...job done.
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