2003 Discovery SE with Secondary Air

Current codes are : P0300 and P0304

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Alright, I'm throwing my hand up in the air and reaching out to you all with this one.

MONTHS ago, I started getting an intermittent cylinder misfire coming from 4 and 7, I put some cleaner through, no help. I checked the plugs and wires. All good. It was intermittent so I let it ride for a touch, only small trips that resulted in no misfires. Then it started to be more and more consistent and I sought out some help.

I took it to Mechanic A (a hugely popular garage that I've trusted forever and specifies in Rovers and other imports) they looked at the plugs and wires, checked compression and tested the coils. All good. The guy told me that his next step would be the injectors, but I've done so much of the work myself I couldn't abide the 400 EACH they we're gonna charge me to do it so I took her home and did it myself replacing all of the injectors (I replaced the manifold gasket and the fuel pump while I was at it). Ran great for fifteen minutes then started burping again.

A few weeks later I took it to Mechanic B to get a second opinion (also a great specialized garage) they went all through it and replaced the intake piping after the MAF saying it was cracked and that may have been the source of odd air regulation, they also replaced the battery and fixed a loose battery cable. They still saw issues and wanted to replace the coils next, but that bill was starting to get high again so I again took it home and replaced them myself with OEM coils and new wires. Because I LOOOOOOOOVE taking the upper manifold of and on a million times.

This time I was in luck and she ran SUPER smooth... for a week. Now its back to the intermittent misfire

Anyone have any ideas? My brain is tired.

 

“Anyone have ideas”
Im not the expert, but the first idea I have is that in the 2 times you worked on it, you disturbed something that “fixed” the issue, maybe a plug that’s a bit loose, a bad wire that you moved into contact, a loose vacuum hose etc.

 

I order the 62 dollar fuel injector set off of Amazon for our DD about a year and half ago. Had the little disks breaking on ours and I had ran out of spares. Also needed new o rings as mine were starting to get hard and some cracked.

I figured if they failed out of the box, I'd get my money back. Pulling the upper intake to access the fuel rail isn't difficult. It's a 2 hour job tops with a few beers in between.

I used some shindaiwa brand gear box grease on the top and bottom o rings on install. When the engine was pulled 6 weeks ago for sleeve pinning and a 4.6 rotating assembly upgrade the injectors pulled out and slid back in like I greased it yesterday.

Even picked up a Pump on for a whole 14mpg when I installed them.

They make a little light for testing the firing of the injectors. Before install I'd pull the fuel pump relay and have a helper turn the engine over to verify they are getting power. These rigs are also getting older and the wiring insulation isn't exactly top notch. Look for cracked wiring that could be shorting.

I'm not sure I'd start chasing wiring back to the ECU at this point but if I wasn't getting fire at the offending injector plugs that's where you're headed.

So far the Amazon coils and injectors are top notch. I stick to Bosch MAF (VW part number), Walker or Bosch O2 sensors and OEM Rover cps. So far I've not had any issues with any of them.

 

Pull the plug on #4 and check it,that is your current misfire then work backwards

 

4&7 are on the same siamesed coil, 98% chance it is a bad coil. Swap coils left to right to test.

 

The coils are brand new Bosh, plus i had this problem before I swapped them.

 

Well 4&7 are on the siamesed coil, so if its not the coil then it is likely the trigger wire to the coil.

 

Exactly what I thought. Had the same issue a while ago - pin backed out of the coil pack connector.

 

I'm going to get on it this weekend then, I've taken off the manifold so many times now that it's pretty second nature. Once I pull the connector for that side will the slipped pin or pins be pretty obvious?

 

It should be. Take a close look at the front and rear of the connector for a pin that's pushed back or a broken wire.

I spliced in (solder and marine grade heat shrink) new connectors on both sides a while ago.

Good luck!