Good evening all.

I have 2000 v70r with 144k miles. This past saturday i had 2 faults stored in my obd. 3503 misfire & 3543 misfire in cylinder #4. I swapped ignition coils with cylinder #1. I also pulled & inspect cylinder #4 spark plug finding spark plugs was in good condition. I just replaced the spark plugs about two months ago with the Bosch equivalent to the oem spark plugs. Reset OBD drove home. Sunday when i got into my car and started it up, Check engine light was on. Scan obd today finding same faults 3503 & 3543. I stumped. I am going to check wiring at taht cylinder. I always run premium gas only.

Thx for the help.

Update:

Did a compression test on my car last night. Low compression on cylinder #4. #1 100psi,#2 100, #3 85 #4 45 & #5 100.

What is my next move here?

Thx.

Did you do that compression check on a warm engine or after it had been sitting for a while?

When I did my timing belt, I was also replacing the spark plugs. I decided since I had them out, I would check the compression. The car had not been started for several days. When I checked it, I thought I had somehow bent valves during the job since compression was wide ranging with one down to 80 psi.

I went ahead and started it and warmed it up and ran the compression test again. All cylinders were 195 to 200 psi. I suspect the car has hydraulic cam followers that had bled off while sitting, but I never verified that to be so. Are they hydraulic?

Charley

Well, at least it is not the plugs or coils - darn. Did you try adding oil to each cylinder and repeating the test? That sould boost the compression to 150 psi in the good cylinders. If #4 stays at 45-50, then it could be a bad piston ring.

You are in for a major job. Either a headgasket failed (most likely) or a pair of valves are bent (least likely if the Tbelt lines up correctly). In either case the head gets removed and gasket gets replaced. In most cases the head will not need to be milled as they seldom warp, but the valve stem seals should be replaced while exposed.

There is an outfit in Florida that will send you a reconditioned head, new valves/seats, etc. for a 'small' fee.
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My back feels better when I sit in a Volvo seat

Those 2 misfire codes are for cylinder #3, generated when a misfire happens at engine start up and before 1000 rpm.

It's possible that an injector is clogged or not spraying correctly, or if the piston head looks shiney (flash light needed), a leaky head gasket.

Are the new spark plugs copper core? That's what the engine wants.

But checking the wiring for the coils and injectors is the best thing. Also check the antifreeze level.
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My back feels better when I sit in a Volvo seat

Reset OBD. Scanned obd yesterday evening. Same faults returned, 3503 & 3543 Misfire in cylinder #4. Check engine light was not on when i scanned my car. I going to try to do a compression test this evening. I think i may have a faulty #4 fuel injector. Thoughts?

If the #4 plug is clean, with the engine idling just pull the injector plug and see if the rpm changes. Also verify that the plug for the coil at #4 is solidly plugged in (engine off).

Pulling the coil and spark plug, connecting both together and grounding the plug will show you if there is a spark when cranking. The plug must be grounded so that the coil does not get overcharged and die.

The CEL not being on means that the codes are pending. It takes several starts to collect enough of the same code to trigger the CEL to light up. Once the problem is fixed, the codes should go away on their own.
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My back feels better when I sit in a Volvo seat

Update:

So last Thursday evneing I replaced #4 ignition coil with new part. Scanned obd finding cat fault. Cleared fault. This past weekend check engine light returned. Got to work today and scan obd again. Same faults. 4801, catalytic converter efficiency, 3503, mifire and 3543, cylinder #4 misfire. Talked to my boss about my issue. He thinks i should do compression test. I work at an indy repair shop. One thing i did noticed when replacing that ignition coil was the bolt the holds the coil in place was loose. I could remove the bolt with my fingers.Looks to be stripped and would need heliocoil to rethread. Could this be the source of my misfire?

Thank you.

I think that bolt is only used to keep the coil in place and from dislodging when on a bumpy road. The spark plug for #4 is clean? It should look awful.

After checking the compression, dribble about 1 tablespoon of oil in the cylinder and check the compression again - a broken ring is rare but you need to look for it.

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My back feels better when I sit in a Volvo seat

Maybe a bad plug wire? Or Rotor cap? Look at the wires in the dark
and see if there's any corona.

Bill