Hunting random misfire on 4200

[Advancedme]

Recently I noticed a misfire at idle, just a single misfire once every few seconds at idle. When ever I revved the engine it ran clean on all 8.

However driving the car later it started misfiring and losing power accross the cylinders. I limped the car home and turned it off.

When I came back to it the start up was perfect and after a few seconds a tiny misfire started. 30 seconds later it was struggling to run at all.

I replaced the MAF sensor with a new one and found no improvement. I removed all of the plugs and burned them clean. Refitted the plugs fired it up and for a moment believed it was fixed. It wasn't.

I checked o2 readings and at idle with the slight miss all trims were uniform and post cat sensors were cycling up and down.

I then fitted fuel pressure gauges to the shraeder valves on the the fuel rails. I removed the valve and then used -4 aeroquip fittings to connect to gauges. I strongly believed a fuel pump was dying but when the heavy misfiring and popping occurred both rails had perfect 45psi of fuel. The both also pump up to that immediately so I am satisfied it's not the pumps.

Next thing I checked were the injectors.

I found two with poor spray pattern on one side and these were down 3% & 5% on flow also. See photo.
Tried cleaning them ultrasonically but to no avail. Luckily I found some second hand on eBay and when put with my other 6 I have a set of 8 within 1% of each other!

Surely this has to fix it right? Nope

Runs smoother but after a few seconds the little misfire comes back.

I've ordered a couple of coils and new spark plugs and hope it's a cool pack... But quite odd symptoms for me.


Question to you guys. Had any ever had any issues with the EGR valves sticking? It reminds me of an issue I once had with a Honda. Anyone have any experience with the EGR on this engine?

Many thanks

 

[Oneball]

There’s no EGR on a 4200. Do you mean the secondary air system?

Have you tried disconnecting each coil pack one by one?

I’d also try looking for a vacuum leak. There’s a pipe that joins the two sides of the secondary air system together that’s known to corrode. Maybe manifold sealing, throttle body etc.

 

[mjheathcote]

What does an obd2 reader report.
I had a misfire, came up on two cylinders.
Experimented with swopping coil packs around, still the same two cylinders, then moved the plugs, the misfiring cylinders moved with the two plugs. Changed all 8 plugs for new ones, problem solved. Can't explain why two plugs decided to fail at the same time though.

 

[hashluck]

Get a code reader on it. Will most likely point you at the cylinder(s) and you can, as stated above, easily fault find from there. Seems like you have done a lot of work that was not needed so far. Coil pack would be my bet and they could get worse when hot. But give up the guessing and get a reader.

 

[conaero]

You need codes. If no engine light on/no codes then change the plugs.

If that doesn’t sort it I would suspect a blocked secondary cat where the primary has grenaded and blocked it.

 

[Advancedme]

No engine light. No codes present or historical.
Even when it's misfiring terribly it does not register any faults at all.