EMI (electromagnetic interference) Problems

[ThanasisPolitis]

 

Hello all,

I've been experiencing some unusual interference issues with my car's electronics. I have an Acewell ACE-7659 dashboard, and both the temperature and speedometer sensors are giving erratic readings when the engine is running.

After speaking with Acewell and running some tests, we've concluded that the issue seems to be interference when the coil is on. The coil is an AccuSpark red, mounted right under the distributor on the engine block, and I'm using AccuSpark 8mm silicone HT leads.

I also had the car on a rolling road, and the mechanic noticed the interference too, as his timing gun was randomly lighting up on its own!

Has anyone else had similar issues with interference? Any advice would be appreciated!

[IanS]

what spark plugs are you using?

ones with a resistor have R as part of there part number. For instance on my pinto engine I use NGK APR6FS which has a R as part of the code.

The resistor acts to reduce interference. I understand that the AccuSpark leads are resistive. resistive.

[ThanasisPolitis]

I am using NGK AP7FS …

The AccuSpark plugs are the standard 8mm soft silicone, carbon core, high resistance ones…

[IanS]

You could try APR7FS.

[ThanasisPolitis]

40 minutes ago, IanS said:

You could try APR7FS.

I can’t seem to find any when googling it…

[IanS]

Yes I assumed that there would be a suppressed version.

APR6FS could be used to prove that this is the problem.

[ThanasisPolitis]

Just now, IanS said:

Yes I assumed that there would be a suppressed version.

APR6FS could be used to prove that this is the problem.

I just tuned the car in a rolling road and I am wondering if I go to the APR6FS will it throw the tune off?

[IanS]

The plug has the same fitting and will fire the near enough the same. It is one heat range hotter so at full power it might have problems but at low to medium power it could be used to see if this is the problem.

APR6FS is the recommended plug for 2l Pinto engines.

[Foz]

Interference often happens when you've got a bad earth somewhere, trouble is it can be a real pain to find.

I'd check any ground connections you can find.  Don't forget the dizzy itself, you should have a good ground from it all the way back to the battery -ve but I've often found some resistance between the points (or module) and the block.  Of course, now that I've said that it will probably be something totally different

[ThanasisPolitis]

6 minutes ago, Foz said:

Don't forget the dizzy itself, you should have a good ground from it all the way back to the battery -ve 

Thank you!

very interesting point, I do not think the dizzy has an earth wire… it earths through the engine block…

[Foz]

I've had problems with distributors in the past where the body of the distributor doesn't make good contact with the engine block (normally due to a bit of corrosion), and also there is usually a flexible wire from the points (sensor) mounting plate, connecting it to the body of the dizzy, which I have seen broken.

A quick resistance check from the mounting plate in the dizzy to the negative of the battery should read pretty much short circuit - if it does then all's good and ignore my ramblings

[Sparepart]

In the Sierra donor car that I used, the ignition system had two things not mentioned so far in this thread. I think both were to try and prevent noise on the AM/FM radio and also protect the early form of electronic ignition. The first was a galvanised steel shroud fitted tightly around the top of the distributor, where the rotor arm whizzes around, the shroud had/has a very visible earth strap to the main body of the distributor. This is a ford part, but it's somewhere in one of my bits piles, and I can't find any references to it on the web, I'll try and find it. I attach a photo of one from a different distributor so you can see what I mean. Anyway I assume that this shroud helps remove some of the EMI associated with the small sparks that jump the gap between the rotor arm and the pick up pegs in the cap. I would think that this gap has to be significant to allow for a worn distributor shaft.  The second device is not for EMI, it serves to remove voltage spikes in the loom caused by the primary winding of the ignition coil. This takes the form of a capacitor connected between the +ve connection on the coil and earth. The Ford part number on mine is 71HM-12A 019-A2A it is rated at 2.2 micro farad 110v.

 

Edited October 20 by Sparepart
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[ThanasisPolitis]

Very interesting… 

thank you all for your input, much appreciated!

I think the culprit might be from the electronic rev limiter I have bolted in the back of the dashboard. 

I have run some two cables from the positive and negative of the coil across the engine bay following the path of the original wire loom. 

Now I need the rain to stop so I can go and test this.
 

[ThanasisPolitis]

So, done some tests and it seems that the electronic rev limiter and it’s cabling is not the source of the interference.

I started up the car and noticed that the tachometer was counting and stable until the l revved the engine above 2k rpm for the alternator to kick in —which it did — and then the tachometer stopped working all together and the temp gauge was fluctuating…

I am now wondering if the source of interference is the alternator itself?

It has two brown cables in the back of it, a thick and a thin one.

As far as the ground, I get continuity between the block and the alternator as well as with other ground points around the car…

Should the alternator have a dedicated ground cable instead of just relying on the connection with the block?

 

 

Edited October 25 by ThanasisPolitis

[IanS]

Alternators ground through their mounting.

It is worth checking that there is no paint or corrosion on the mounting points both the bracket to the alternator and bracket to engine block.

If the car starts then the engine return to the battery is good or the starter would not get enough current.

If the rectifier in the alternator has a diode gone it can put out a lot of noise.

The thick cable takes the charging current to the battery.

The thin cable normally goes to the ignition light on the dash board.

The fact that the engine revs to 2K before the alternator kicks in shows a problem as the alternator should start charging below 600RPM engine speed. This could be down to the alternator having the wrong bulb in the dash or a wiring error or internal problems in the alternator.