Had misfire checked out today

[grahamw48]

Well chaps, maybe something to chew over...I'll just write out the mechanic's report.

This is Brummiewedge's old car, with the 1995 Chimaera 400HC motor with new Real Steel 220/218 cam fitted, with matching Chim ECU and AFM.
I wanted them (first class outfit in Middlesbrough, incidentally) to checkout a misfire at higher revs.
.....

Diagnostic testing

Recommendations:

"Initial investigations showed over-advanced ignition, giving rise to some misfiring.
Inspection showed some wear in advance/retard mechanism.

-Ignition retarded to give a max advance of 35deg @ 4500rpm.
This improved misfiring, but tends to de-stabilise idle quietly.
No amount of base idle and fuelling adjustments would settle idle.
Modified camshaft will have adverse effect on idle, but suspect A/flow sensor problem also.

Suggest replace distributor and A/flow sensor.

NOTE:
Unable to establish whether this has closed loop management.
If original fitted with O2 sensor, this will cause problems."


So, looks like a new distributor is in order.
Any of you guys care to comment on what is mostly gobblegook to me ?

NB. This implies no criticism of good old Brummiewedge.

[GreenV8S]

If it's running a Chim engine, is it also running the hotwire setup from the Chim or is it running the flapper setup?

[rev-erend]

I'd say - disconnect the vacuum advance / retard pipe : block the pipe and the pipe on the manifold.

If this works - then you know for sure that it's the mechanical advance / retard causing the problem.

Doing this means that your max advance will be about 28 degrees before TDC..

Having no lamba sensors on the wedge - should means that you just have no closed loop (super economy) but I believe the ECU will cope OK without this. All wedges with 14CUX (& hotwire) run like this anyway..

Let us know if you still have the problem after this simple mod.

Here's a picture of how to do it :

Edited by rev-erend on Friday 2nd June 19:33

[grahamw48]

GreenV8S said:

If it's running a Chim engine, is it also running the hotwire setup from the Chim or is it running the flapper setup?

It's hotwire (was hotwire originally on the Wedge engine too).

[grahamw48]

Thanks rev-erend.

I'll give that a try.

The mech said that it had been originally 45deg advanced.

Hey, if only Haynes pictures had been so clear.

[rev-erend]

grahamw48 said:

Thanks rev-erend. I'll give that a try. The mech said that it had been originally 45deg advanced. Hey, if only Haynes pictures had been so clear.

I think 45 degrees would be too much..

Max would probably be 36~38 degrees at 6000 rpm under the lightest load - with 28 (set at 4000 rpm) being the ideal figure for full throttle.

[grahamw48]

Ok rev, I've just nipped out and done your cut'n'shut mod.

I'm off to Croft motor racing tomorrow, so will test it out on the way.

What's this Airflow sensor thingy ?
Is that likely to be a straightforward (and reasonably cheap) part to replace ?

The mech also said that the dist. base plate wasn't springing back always...sort of sticking sometimes.
I suppose it would be sensible to fit a new one, though I believe they're around £150 ?

I gave away my bible with the 390SE.

[chunder]

If timing has now been set at 35 at 4500 and it still misfires at high revs I would look at the ignition and check leads and maybe try changing the coil. If you use a digital multimeter to check the resistance of the coil and let me know what the reading is I'll check to see what it should be.

If the ECU is the original or even if it is off the Chim unless it has been re-programmed on a RR with that engine in the wedge then fuelling will not be accurate. The 4 litre Chim engine and the 4 litre wedge engine have different requirements and the different exhaust alone will mean different fuel requirements. If it's off the Chim then I believe they use twin O2 sensors and it won't work properly if they are not fitted. A friend of mine with a Griff 500 had an O2 sensor fail which caused massive under fuelling as the ECU tried to maintain a good AFR.

The different cam will also affect fuelling requirements and depending on charcteristics may make it lumpy at idle. If it's not a simple ignition or fuelling problem and persists maybe Mark Adams could offer some advice.

[grahamw48]

Thanks Chunder.
Apparently the coil is quite new, and okay, as is the rest of the ignition side.
In fact the mech gave the rest of the engine a clean bill of health.

I haven't found the tickover to be a problem (I avoid traffic anyway), and the stepper seems to come in properly and reduce the revs back down.

To be honest, the car doesn't feel much different to my 390 powerwise, perhaps a bit more, but not as free-revving as the 390, which didn't appear to have a limiter.

The problem before - much worse when hot - was a sort of staccato misfiring when foot hard down at anything over 4000 revs (approx). Felt like a rev limiter.
The engine didn't run hot, and fuel consumption seemed quite reasonable (for a BBW ).

I've now disconnected and plugged the vac. advance, so I'll see what effect that has today.
Also, when I took the car home yesterday, she was a bit low on fuel, so I didn't give her full welly. She did seem improved though, and no misfire, but no spirited driving either...

I agree it is likely that running with a different exhaust set-up, SOME adjustment is probably needed. Oxygen sensors and things are beyond me I'm afraid, though I understand the principle. This could just be that glasses are required to see them...a problem affecting every aspect of a middle-aged person's life, unfortunately.

A session with Mark Adams probably would be the answer, in this sort of situation.
Anyone know what the cost is likely to be ?
Also a new distributor.

The good news is that I got my insurance renewal from Classicline this morning and it was £198 fully comp.
Eat yer heart out twentsomethings.

[wedg1e]

That 'staccato misfire' is exactly what my car had last year when the ignition pickup was on its way out. Acted like a 5300 rpm rev limiter.
Changed it: saw 6500 straight off

[GreenV8S]

grahamw48 said:

GreenV8S said: If it's running a Chim engine, is it also running the hotwire setup from the Chim or is it running the flapper setup? It's hotwire (was hotwire originally on the Wedge engine too).

Which ECU are you running - the original Wedge one, or the one from the car that donated the engine? If the latter, has it been converted to suit the engine's new home? (I mean in terms of selecting open loop mode, and making sure the corresponding map was suiable for the car. This might require a rechip and possibly a rolling road session.)

[grahamw48]

The ECU fitted is the (matching) Chim one.
Brummiewedge did say that he'd fitted a green tuning resistor ().

I've been out and about today (including a visit to wedg1e), and the car does seem to go really well now, certainly a big improvement.

This is also with the vacuum advance pipe removed and plugged.

Tickover is around 1000rpm, with slight hunting up and down. The car seems to have more lowdown grunt, and can be taken right up the revs with plenty of power there also. No pinking or misfiring, except just once when really revving her, so possibly the limiter.
Fuel consumption appears quite good, considering a fair amount of footdown stuff.

I'm sure things could be further improved with a RR session of course, and I think distributor replacment would make sense before any further attempts at tuning.

Yes, I was thinking about a re-chip to take into account the changes made.

[GreenV8S]

Green is correct for open loop operation (i.e. with no lambda sensors), although it's not safe to assume that the corresponding map was set up to suit that engine if the engine was originally run closed loop with lambda sensors and cats.

Given the problems you're having, and the substantial changes you've made, it would probably be sensible to have Mark Adams give the whole system a health check and set it up for you.

[grahamw48]

Thanks for your input.

I think I will be going down the route you've suggested.

Since price and Mark Adams never seem to appear in the same sentence, I must assume it means A LOT.

[chunder]

grahamw48 said:

Since price and Mark Adams never seem to appear in the same sentence, I must assume it means A LOT.

If you are going to be tempted to develop the engine further I would consider fitting Motec or similar. Mark Adams is not an option down here and I can't afford a top brand system so I'm slowly amassing the bits required to go closed loop and ignition with a megasquirt system.
Does sound like basically yours is there and only some fine tuning may be required.

[grahamw48]

Agree Chunder.

I would be interested in putting one of these more advanced engine management systems on.

[Snow Mole]

Graham
I've just picked up a distributor on ebay and if you wish to borrow it, let me know. Have you tried R & P Woods in Newcastle? They have a RR and also very good knowledge of TVR's. Sorted mine out a treat for a very reasonable price. Whilst I was in they were correcting an Aston owners pile of trouble from the main dealer....
PM me if you need their number.
Richard

[grahamw48]

Oooh that sounds interesting Richard.

Would you sell the distributor ?

[rev-erend]

As the mod worked - then the problem is indeed with the dizzy..

Either replace it or stick with the mod.

It will cost you a couple of mpg but not a huge amout if you are not a light throttle driver.

[grahamw48]

Yes, thanks for the advice rev-erend, it does seemed to have done the trick, but I realise that replacement of the part is the proper solution.

rev-erend said:

It will cost you a couple of mpg but not a huge amout if you are not a light throttle driver.

Oh, but don't we all set out with that noble intention...lol!