Car Misfiring - Ignition Amp?

[stevec205gti 0]

My standard 1.9 is surffer from ignition woes once again. I've got a slight misfire that's noticeable throughout the rev range well slowly revving the engine, and a noticeable misfire at normal cruising speeds (2k to 3k rouughly) on a light throttle. I believe the misfire is still there under acceleration but is not as easy to detect. This misfire has been around for ages and I've not been able to trace it. I am also once again starting to get the standard ignition amp failure mode of the ignition cutting briefly every now and again. This is the 3rd ignition amp I've got through in 4 years, and it's getting to be a royal pain in the backside. I've changed all ignition parts except the dizzy over the months, and the misfire's not gone.

 

Anyone had anything similar? I know that the wire that runs from the dizzy to the amp has some input as to controlling the amp to charge the coil - does anyone know if there's something in the dizzy internals that would contribute to the misfire. I have also read (though it was in the Haynes book of lies) that failure to discharge the coil properly and/or at the correct time can lead to coil and ignition amp failure, so does anyone think it's feasible that the misfire can help degrade the amp.

 

Thoughts and feed back welcome. Discuss........

[Rob_the_Sparky 9]

I've had a couple of different ignition amp failures:

 

1) Non-starting but ran fine once started.

2) ignition cutting on acceleration causing kangerooing. Intermittant problem leading eventually to total failure.

 

Theories on reasons:

 

1) The output from the dizzy is very weak at low revs, particularly so at cranking speeds. Therefore it seems that the input side of the ignition amp is becoming "deaf" so nothing when cranking but OK when running.

 

Note: the AA checked the amp with test kit for the job but have since proven that the igniotn amp was the problem. Also this problem gradually became worse, occasionally taking longer to fire in the morning (less than once a week) eventually leading to complete non-starting.

 

2) This looks like the output side of the ignition amp is struggling to drive the coil, maybe overheating? Certainly it started fairly suddenly and apeared to cure itself later (after much fiddling, hence thought it was fixed). When it eventually died it was in stationary traffic in warm weather and I found that no heatsink compound had been used. Therefore it would seem that this is an output side problem leading to overheating and eventualy failure.

 

 

Yours sounds like 2) to me and it sounds feasable that the coil could fail in such a way to draw more current than normal (stressing the ignition amp) but still generate a spark. Not using heatsink compound would also contribute to the problem (my new amp came without and had to buy some from MAPLIN). Worth a try to replace coil and amp this time.

 

Rob

[stevec205gti 0]

Cheers for your input Rob

 

I would normally have put this done to overheating as well, but there's plenty of HSC applied, as I managed to get a tube from work. Also, the failure doesn't seem consistant with run time. It first failed again when my missus was driving it - it had been running for 15 minutes, the last 5 at about 70mph. I then had the car the next day after changing plug leads (I had been unable to find one to run from the coil to cap last time I changed them so went out and tracked one down). After this I drove around for about an hour, half the time giving it some beans, and the last half hour at constant 60mph - all this without any problems. Driving too and from work yesterday was fine, but then trying to go out last night and it first dropped out after about 10 minutes, then every couple of minutes after that.

 

Also, the coil and ignition amp were both renewed at the same time last time the problem occurred.

 

I think I'm going to have a spend a lot of time with a multimeter looking for intermittent breaks in the wiring/connections to see if I can come up with anything, as well as looking for other more electronic issues.

 

Damn 80's hot hatches!!!!

[Rob_the_Sparky 9]

Yeah. When my 309 was playing silly buggers (number 2) it started on the way home on a 10 miinutes drive and repeated this from cold. Some fiddling later it appeared fine, then started doing it again. Then was consistent from cold for about a week (completely undrivable). Again after much swearing and various parts being changed it appeared to be fine. Then about 20 mins from home in a queue in the MWay (of all places) it was running fine, then nothing. Push to hard shoulder and no joy, flattened the battery trying to start it.

 

AA man arrived and in 10 times of trying it fired once and ran for a few seconds, then died.

 

New ignition amp later and it has been reliable ever since (bar blowing a power steering hose all over the exhaust manifold while at a petrol station!!!).

 

E.g. odd, unpredicatable symptoms seem to be the rule!

 

Rob

[stevec205gti 0]

Seems I should just get another one, and hurry up sorting out the XU10 I've got lying in the garage with coil pack ignition!!!!!

[stevec205gti 0]

Does any one have an good idea of how the ignition system works. My basic understanding is that the ignition amp gets a signal from the dizzy (that little black wire that comes out the dizzy) that tells the coil when to charge. The top half of the dizzy then discharges the coil - but if the coil doesn't discharge properly then you can screw the ignition amp.

 

Also, has anyone pulled a distributor to bits to find out what goes on with to trigger the amp - and also if this could be contributing to the constant misfire?

[pug_ham 244 3 Cars]

AFAIK the ecu sends 12v to the coil which then feed's to the ignition amp & from there to the dizzy.

 

The lead from the amp to the dizzy & plug part way along can break down & corrosion inside the plug will cause problems. I've seen two cars with plugs at the dizzy that have been held together by a strand or two of wire instead of the full wire. Neither ran 100% all the time.

 

Graham.

[Martin@PRD 0]

Can you put your hand on your heart and say its defiantly the ignition?

 

Misfire between 2-3k can also be down to fuel pressure at this is where injectors are most efficient, I have had a few cars my way over the years with a blip and a slight misfire and where down to the course of the following

 

1. Airflow meter - the car was used to commute on the motorway where 2-3k was most commonly used for long periods of time, this slowly worn the tracks on the board which then confused the Ecu, when this point was meet by the pick up it gave the feeling the car had a flat spot with a misfire, this was cured by our own reconditioned afm.

 

2. Fuel pump - Not only can it be the failure of the pump but also regulator, a split vacuum pipe or loose pipe on the pump it self (clip broken)

 

3. Distributor and signal wire - These are a royal pain in the arse as its so over looked, high mileage Distributors suffer from bearing/bush failure and this then increases the end float and then basically it then collapses. If shielded signal wire was to split or break then this will lead to misfires which in turn can confused ignition amp which may lead to over heating.

 

4. - Ignition amp - if not properly insulted to the alloy plate for disruption of heat then it will over heat and course allsorts of problems.

 

Other thing to take into account

 

5. Burnt out valves

 

6. Broken injector plug/wire

 

7. Injector failure

 

8. Loose earth leads

 

9. Worn cam lobe

[welshpug 1,657]

dirty earths! gavwe the main one on the alloy plate the amp and coild is bolted to a good clean and rub down with fine wet and dry and also the battery terminals and I now have a stable idle speed.