Idling and misfire my new chimp :-(

[mattbridges]

Hello all - this is my first post - sorry it's a biggie.

I bought my 1999 Chimaera 450 yesterday (my second Chimaera 450), it has 65K on the clock but the clincer was the as new chassis and replaced diff, the fact almost 18K has been spent on servicing and/or repair work etc - keeping it tip top. It's also been in the same family since new with all receipts and paperwork from new.


Run home was fine (170+ miles) that is until the last 30/40 miles in traffic. The problem was stalling and misfiring. The misfiring occurred under 2000 rpm and at idle. At idle the engine would settle at 900 rpm for a few moments then hunt from 900 up to 1200 then down to 500 where it would miss, try to recover, then stall if I didn't press the throttle. When driving through town if felt like the transmission was catching especially around round-abouts or at low speeds making me always feel like I needed to be in a lower gear. Anything above 2000 rpm was fine with no noticeable hesitation or lack of power.

Looks like it's been a recurring problem.
First problem appeared in March 01 - Stepper motor replaced to fix hunting
Then Jun 02 - Ignition module replaced
Then Mar 03 - Replaced Lambda Sensors
Then Apr 03 - Replaced ignition module and coil
Then Jun 06 - Replaced Throttle Potentiometer
Then Jul 07 - Injectors removed and pattern tested cleaned and new spark plugs

Today I've been checking out a few things.

ECU
Everything checks out fine resistances and voltages etc EXCEPT for the road speed sensor
(Followed testing instructions at: http://www.peter.beech1.btinternet.co.uk/TVR/injpr...
The road speed sensor shows 7V all the time regardless of how much the car is moved.

HT Leads
All appeared fine (resistances where all between 8K-14K Ohms)

Stepper Motor
Checked - clean (but re-cleaned to make sure)

Petrol Cap
Made sure it wasn't too tight or creating a vacuum.

Now it's missing cold or warm - more pronounced as the engine temp increases

The only things I haven't check are the plugs - but they were new less than 5 days ago so they shouldn't be a problem. I'm all out of ideas - anyone out there able to point me in a new direction? If not it's off to an indie or dealer :-(

Cheers

Matt

[That Daddy]

Check the distributor cap & rotor arm for starters,inspect both carefully for cracks,burning etc, if in doubt about their condition then renew,try.www.famousfour.com.Then hopefully you can start enjoying your car some more

Edited by That Daddy on Sunday 8th July 22:03

[john p]

I would change the dizzy cap and rotor arm as they are cheap and are known to fail often,if it is not this at least you have them as spares.Make sure the leads are not making contact with the swan neck of the coolant tank as they can earth out on here for some reason causing misfires.It might be worth cleaning the road speed sensor.Is the car missing on all cylinders?

[AlexanderV8]

Agree with That Daddy.
I had what sounds like exactly the same problem as you. Symptoms could seem to point to practically anything!
Mine turned out to be a non Lucas replacement rotor arm causing the problem. The condition looked fine but replacing it with a new one cured the fault. Don't know if it's breakaway angles or gap to distributor contacts which caused the problems but it runs a treat now.
Good luck.

[mattbridges]

john p said:

I would change the dizzy cap and rotor arm as they are cheap and are known to fail often,if it is not this at least you have them as spares.Make sure the leads are not making contact with the swan neck of the coolant tank as they can earth out on here for some reason causing misfires.It might be worth cleaning the road speed sensor.Is the car missing on all cylinders?

Hey John, Daddy and Alexander,

Thanks for the replies.

Not sure if it's one or more - just had another go in it this evening - as soon as the I come to a halt the power drops right down. On the driveway I let it drop and drop to under 500 rpm then applied the throttle really slowly. I got my foot almost halfway to the 'floor/bulkhead' before it responded. Sounds like it's firing but really weak. I don't hear excess unburnt fuel getting into the exhaust (no backfiring etc), just pathetic response then whallop it springs back into life like nothing was ever wrong.

I'll take Daddy and Alexanders and your advice; open the distributor cap - looks pretty new but don't see an receipt for it anywhere but that's no sign, best to look.

Any tips on getting the cap off without having to take the cooling system pipe (rubber) that runs over the top of the dizzy cap?

Cheers

Matt

[AlexanderV8]

Any tips on getting the cap off without having to take the cooling system pipe (rubber) that runs over the top of the dizzy cap?

Cheers

Matt
[/quote]

You'll need to take off the leads from the cap. Make sure you mark them so they go back in the right places if you haven't got a copy of the Steve Heath 'bible' (where there is a good 'which lead goes where' drawing).

You can then unclip the 2 spring clips which hold the cap on. You will probably need a flat bladed screwdriver to unclip the rear one unless you've got really thin fingers! When you put it back on, you push on the curved middle section of the spring until it clips over the retaining lug on the cap.

[mattbridges]

I've not had a chance to take the cap off yet - but.... after leaving it at home yesterday I started it up this morning, it was REALLY really reluctant to get up to 'normal' idle speed, but when it did it sat there happily for about 5 minutes. Took it to work where it promptly started acting up again.

I noticed the temp gauge got up to about 95-100 in traffic (fans cut in and out as needed). Just been back out to check on it again and it's fine starts and idles no problem until the temp gets a bit higher. If I get back and it's not peeeeeeeing down (chimp is too big for my rubbish 1950's garage) I'll get the cap off. I had a quick look this morning and it looks pretty new and un-fouled.

Cheers

[JonathanT]

I had random-but-usually-when-hot idle problems (hunting 200-1500rpm) and stalling when dipping the clutch. The garage found that the ECU contacts were contaminated/dirty and gave them a good clean - that seemed to fix the problem for me.

More recently I had the same hunting problems and checked the ECU contacts and found that the insulation tape glue had "melted" into the big ECU plug. Cleaned it up and it's been fine since.

[coetzeeh]

Matt, as has been mentioned before - there is a batch of dodgy rotor arms in circulation apparently.

Get a rotor arm from a respected dealer before you do anything else.

[chimalsu]

have you checked the vacum advance pipes are all located ok and in good condition theres one across the top of the left side near the plenum to near the dizzy cap that can easily get pulled out

[mattbridges]

Cheers all

I'm sure it's going to be the rotor/dis cap.

Going to check rotor tonight (weather permitting) - any one got a part number for it - is it just the RangeRover part? If it is I'll pop into halfords and pick one up at lunch time.

Thanks for the tip on the ecu I'll check that out too.

[mattbridges]

chimalsu said:

have you checked the vacum advance pipes are all located ok and in good condition theres one across the top of the left side near the plenum to near the dizzy cap that can easily get pulled out

I've checked the vacuum pipes over they looked ok and blew through it to make sure it's not blocked :-)

[Ozstyle]

Hi,
it may also be the road speed sensor as you first mentioned. Tells the ECU that the car is moving and has some thing to do with stepper motor control.

Ozstyle

[Chassis 33]

Any idea when the fuel filter was last replaced, I'd hope on service, but you never know. If this has become clogged it could lead to lean running but probably throughout the rev range, also do you know what fuel pressure you have? The regulator could be in some way duff, and seeing as if works of the plenum vacuum the diaphragm could be leaking.

One thing I've found by accident, and it may be useful for other folks in future who search for this, is that one of the fuel pressure gauges that the likes of Demon Tweeks sell screws directly into the fuel rail if you unscrew the fitting the Schroeder valve goes in. http://www.demon-tweeks.co.uk/products/ProductDeta...

Regards
Iain

Edited for atrocious speeling, and Grammar. Probably little better now!

Edited by Chassis 33 on Tuesday 10th July 11:39

[mattbridges]

Chassis 33 said:

Any idea when the fuel filter was last replaced, I'd hope on service, but you never know. If this has become clogged it could lead to lean running but probably throughout the rev range, also do you know what fuel pressure you have? The regulator could be in some way duff, and seeing as if works of the plenum vacuum the diaphragm could be leaking.

One think I've found by accident, and it may be useful for other folks in future who search for this, is that one of the fuel pressure gauge that the likes of Demon Tweeks sell screws directly into the fuel rail if you unscrew the fitting the Schroeder valve goes in. http://www.demon-tweeks.co.uk/products/ProductDeta...

Regards
Iain

Hi Iain,

Looks like it was done at last service - but thats no indication that it's not screwed. Thanks for the tip. I'll check that out tonight :-)

[Cider Andy]

I'm another one who'd suspect the rotor arm first. I have one here that looks perfect (and did work for a few thousand miles), but it doesn't work now - the car won't even start with it in. Beyond that, are you certain the coolant temperature sensor was in spec throughout the temperature range?

[spend]

Try disconnecting the road speed sensor connection, I assume it is the later version with black box 'splitter' behind the dash. This may fix your idle problem - but be careful when lifting off. It is not the solution, but least it will eliminate/confirm if the road speed sensor circuit is the problem (more than likely the black box rather then the actual sensor BTW)

Dave

[GreenV8S]

I'm starting to sound like a broken record here I know, but to start with I suggest you get it warmed up and idling steadily then unplug the stepper motor. If this cures the symptoms you know the problem is associated with the stepper motor and ECU. If the problem persists you know you have a more fundamental problem and need to look elsewhere, for example fuel pressure, ignition timing, air leaks etc.

It's no problem running with the stepper motor disconnected (in fact I find the car is a heck of a lot nicer to drive because the idle is more predictable when coming to a stop) but if you wanted to adopt this bodge as a permanent 'cure' you need to imobilise the stepper motor or replace it with a bung, because it will gradually creep if left disconnected.

[mattbridges]

GreenV8S said:

I'm starting to sound like a broken record here I know, but to start with I suggest you get it warmed up and idling steadily then unplug the stepper motor. If this cures the symptoms you know the problem is associated with the stepper motor and ECU. If the problem persists you know you have a more fundamental problem and need to look elsewhere, for example fuel pressure, ignition timing, air leaks etc.

It's no problem running with the stepper motor disconnected (in fact I find the car is a heck of a lot nicer to drive because the idle is more predictable when coming to a stop) but if you wanted to adopt this bodge as a permanent 'cure' you need to imobilise the stepper motor or replace it with a bung, because it will gradually creep if left disconnected.

Hi GreenV8S I did try disconnecting the stepper (but I hadn't warmed up) which in hindsight was a stupid thing not to have done. I'll give that a bash tonight too.

[mattbridges]

spend said:

Try disconnecting the road speed sensor connection, I assume it is the later version with black box 'splitter' behind the dash. This may fix your idle problem - but be careful when lifting off. It is not the solution, but least it will eliminate/confirm if the road speed sensor circuit is the problem (more than likely the black box rather then the actual sensor BTW)

Dave

Hey Dave(spend) where about is the road speen sensor connected? I'll give that a go this evening - looks like my girlfriend is going to be scowling at me through the garage door again :-(