Hesitation under acceleration even after ignition system replacement.

[curator23]

My '06 Focus 1.6  is suffering from hesitation during heavy acceleration mostly around 2000 rpm.

Initially I replaced the coil pack, which almost completely fixed the problem.

A few months later, it suddenly got worse. I replaced the spark plugs, and again, the problem was almost completely fixed.

To try to fix that last little bit of stutter, I've also replaced the HT Leads. This has made little to no difference.

If anything, it's more noticeable at lower rpms now, around 1200.

 

The only part of the original ignition system remaining is the ECU.

 

Can anyone suggest another problem that may be causing these symptoms?

Otherwise, is there a recommended technique for testing the coil drive outputs on the ecu?

 

Cheers.

[curator23]

The problem seems to be worse when cold and the oil level is low. Could this be a valve train problem?

Topping up the oil doesn't completely fix it, but it seems like just one cylinder is firing with less power for a single stroke when the problem manifests.

 I'm thinking of running some LiquiMolly 1019 through it at the next oil change.

I'm also going to try cleaning out the injectors. I wouldn't be surprised if I'm looking at two different faults here.

 

[curator23]

I got a P0300 this morning. Multiple/random misfire. Google tells me this could be a vacuum leak.

Other symptoms include erratic idle - check.

You Tube tells me that when the engine is warm the lambda sensor compensates for the excess oxygen and runs normally.

I've sprayed WD40 over all the vacuum hose joints and gaskets I can see with no change in rpm, so I'm now suspecting a dirty MAF.

Hopefully the CarPlan Carb and Air Intake Cleaner I bought is suitable for MAFs.

[curator23]

It doesn't have a MAF. MAP is clean.

Trying a fuel system flush. Will report back in two tanks time.

[curator23]

I think I've solved it:

The valve rocker gasket is leaking and the spark plug well is filling with oil, causing a bad electrical connection.

The leak is mostly at the cylinder 4 end of the engine, which is why I get the misfire on that cylinder, even after swapping both the injectors and spark plugs with cylinder 1.

Swapping the sparkplugs improved conditions for a little while, as I'd cleaned off the oil contamination.

It also may explain why it seems to be worse when the engine is warm, as the viscosity of the oil would be lower and presumably would penetrate further.

I may also have been suffering from dirty injectors, as the fuel system cleaner (1 bottle of Redex and 2 bottles of STP 5-in-1 ultra) seems to have removed the 2k rpm specific misfire.

 

The spark plugs came out as a dry, dirty-dusty tan brown colour, which I understand to mean it's running lean. Not sure if this is an ongoing problem, or if they're permanently stained from earlier poor fuel delivery.

 

I'll report back after swapping the gasket and thoroughly cleaning the sparkplugs and plug well.

[unofix]

I like your theory but it mostly depends on wether you think the oil was getting between the Spark Plug and the HT connector or if you think that the HT circuit was shorting over to the metalwork of the engine block.

oil is a very good insulator and is used in many high voltage switchgear applications especially at sub-stations