Ok, here is the back story:
Bought the Volvo, needs mechanical work. It has both OBD1 and OBD2. Pull the OBD2 fault code: P0304 - misfire in cyl #4. Did the OBD1 test, came back as 5-4-3, 5-4-5, 5-5-4, and 4-5-4. These are all misfire faults.
What i have done:
Replaced distributor cap, rotor, wires and plugs. Same result.
Any suggestions?
How close to one another are the plug wires? That can cause a misfire, if they're closer than 1/2" or so.
Hall-effect sensor malfunction? I don't know the technical term Volvo gives it, but it usually lives under a shield just under the rotor, is it clean down there, or a bit shmutzy? Clean the shmutz out. Check for loose wires, too.
clogged injector, bad cylinder - have you done a compression check? bad head gasket - long shot but possible that it only leaks one way, similar symptoms to bad rings, you can get a kit to test for exhaust in your coolant.
is it missing all the time, or just under load?
Or does it clear up when you rev the eingine?
My last last misfire problem wasn't on a dizzy motor but it turned out to be a bad injector. You can swap them around to see if the misfire changes cylinders.
Plug wires are fine, correctly placed in its corresponding firing order.
The little dust shield was cleaned when i replaced the cap and rotor,
Haven't done a leak down/compression test yet. That's next on my list. I am planning on pulling all the injectors and having them rebuilt and tested. Scared its going to be rings... It misses at idle and under load.
weak fuel pump, bad injectors, clogged fuel filter, head gasket, intake gasket leak, faulty air meter. On the mechanical side, worn rings/cylinder/piston.
In reply to triumph5:
For the most part yes, it eases up with rpm.
Since it's missing, what sound like all the time--idle and under load--sound like either a bad injector, or, your compression check will not be nice. I'd bet bad injector, being optimistic.
I don't know if this is possible with that particular engine's set up, but can you pull the injector from another cylinder and swap the two to see if you get the same results, or if the problem moves with the injector?
yea, was going to try that. Did that with the plug wires to see if the mis would follow, but it remained in cylinder 4. I am being optimistic in hoping its a bad injector. My dad told me he would rebuild and bench test all 5 for $125 or $25 a piece.
Going to do a compression test later today.... Wish me luck!
Hall effect sensors are infalible in Hondas and Toyotas and the like, but not in Volvos. Check that thing closely, twiddle the wires while its running to see if you can make it skip a beat. Many a Volvo has a subtly broken wire at that insulating block or gromet.
The Volvo: 4,5 or 6 cylinder? 140, 240, 740, 850,?
Its the 5 cylinder. Non-turbo
Quick ignition check is to pull each plug wire up with the engine running, and listen to the sound of the spark. Should be strong- if its less so on a cylinder, figure out why. Also, make sure the spark is going to the plug, not out the side of the boot. The early 5's have been known to burn valves, but its sure not an everyday occurance. Compression test there, obviously. Easiest injector test is to swap the bad cylinders injector to another cylinder, and see if the problem follows or stays. Use a stethoscope to listen for the proper clicking of said injector as well- Harnesses are not the trouble they used to be on the 240-740's, but who knows.
Quick vacuum leak test is to take a cup of water and pour it over the manifold near the cylinder head- sucking noises and rough running means you are pulling water past the manifold gasket.
Compression Test:
Cyl1 - 130
Cyl2 - 120
Cyl3 - 120
Cyl4 - 0 
Cyl5 - 120
In reply to DukeOfUndersteer:
Head in hand. 0! Never seen a 0 cylinder before.
just whip that head off, and I'm sure some JB Weld in the right place.......
Did you do a leak-down, too?
Thats next, gonna borrow the compressor from next door since we dont have one. I want to take the valve cover off to see if all the valves are moving
Edit: And need to find TDC too...
A stuck open valve would go a long way to explaining a zero reading. And that's probably where the problem is, pondering it for a while. All the other cylinders are too consistent for this to be "general wear and tear".
There is a Volvo guy telling me it could be a massive blown head gasket or one of the cam lobes is completely rounded off.... Checking tomorrow
It'll be a burnt valve. Headgasket would manifest other, more spectacular symptoms, and a hole in a piston would do the same. You made no use of the words "puke", or "fog" or "smokes like a bitch".
Now go online and read up on the cover and head removal, and the tools you'll need to borrow or make to get the cams back in time. Its a time consumer, but not tragically difficult. If its got variable cam timing, read the cam timing instructions several times, please. Its easier the second time, but more expensive when you have to buy ALL the valves instead of just one.
Lil hint: the cam belt is not installed at tdc#1.
So i read that i will need this Cam Locking tool. Others have taken the grassroots way () of locking them without purchasing this tool.
Head removal looks pretty straight forward and hope not to run into many hiccups...
pic of the tool:
I think that is to lock the cams when you are changing the timing belt, not for when you have to remove the cams, as you will. The tool you need looks like this, and locks the back end of the cams so you can reinstall the non-keyed sprockets in the proper spot:
DukeOfUndersteer wrote: So i read that i will need this Cam Locking tool. Others have taken the grassroots way (
Those engines seem to blow head gaskets a lot. The ones i have seen usually made clouds of steam though.
In reply to Streetwiseguy:
Ah. Where would i be able to find one such tool?
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