The Misfire Thread
Camel Trophy
Joined: Nov 2012
Posts: 3,717
Likes: 248
From: Longview, Texas
"Low compression and slipped sleeves or a cracked block on a cylinder can cause misfires."
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In my experience, low compression does not, generally, cause misfire, nor does slipped sleeves, but what often does cause misfires, especially ones that many guys cannot diagnose----after checking items detailed above, sometimes repeatedly, they give up---is one or more minute cracks in aluminum wall behind one or more liners, due to that aluminum wall being, comparatively, quite thin. Most of the time, the cracking is directly caused from overheating of engine, and indirectly to some degree, from the stretch head bolts putting serious stress on specific area of block, or very close to it, (almost always directly across from base of head bolt, where cracking occurs most of the time. Such cracking is direct cause, most of the time, to the liners coming loose, "slipped liners," but the block cracking can and does happen often, with the liners not coming loose, at least for a reasonably long period of time anyway. The crack in aluminum wall allows coolant, coolant jacket is short distance from the thin aluminum wall, into the interior surface of liner(s), moves upward (sometimes downward into oil pan) and into one or more cylinders, which directly spark plug from firing, thus misfiring. This happens a lot more often than most people realize, with the Rover engine, and more often than most people want to admit.
_______________________
In my experience, low compression does not, generally, cause misfire, nor does slipped sleeves, but what often does cause misfires, especially ones that many guys cannot diagnose----after checking items detailed above, sometimes repeatedly, they give up---is one or more minute cracks in aluminum wall behind one or more liners, due to that aluminum wall being, comparatively, quite thin. Most of the time, the cracking is directly caused from overheating of engine, and indirectly to some degree, from the stretch head bolts putting serious stress on specific area of block, or very close to it, (almost always directly across from base of head bolt, where cracking occurs most of the time. Such cracking is direct cause, most of the time, to the liners coming loose, "slipped liners," but the block cracking can and does happen often, with the liners not coming loose, at least for a reasonably long period of time anyway. The crack in aluminum wall allows coolant, coolant jacket is short distance from the thin aluminum wall, into the interior surface of liner(s), moves upward (sometimes downward into oil pan) and into one or more cylinders, which directly spark plug from firing, thus misfiring. This happens a lot more often than most people realize, with the Rover engine, and more often than most people want to admit.
Last edited by Charlie_V; Jan 17, 2014 at 03:25 PM.
Pro Wrench
Joined: Apr 2008
Posts: 1,475
Likes: 37
The ECM uses cam sensor signal, to know what cylinder should have just fired and didn't(there is no such thing as 180 out with the ignition system, as it sparks each cylinder on both compression and exhaust). This means that an issue with the reluctor on the flywheel can cause a misfire fault as well, but would do so with two cylinders at a time. Makes it easy, right?
However, the two cylinders that would be flagged would be two opposite in firing order, 1-6 2-3 4-7 5-8, this is also the set up for the waste spark/coil sharing. A bad coil(as in electrically bad, not physical damage to a HT lead pin) will always cause misfires on two of the cylinders above.
Also, an issue caused by the CKP reading, would effect spark, which is what you would lose for a bad coil too. Luckily, you 'should' get a code for a CKP error, if it is losing its signal.
Camel Trophy
Joined: Nov 2012
Posts: 3,717
Likes: 248
From: Longview, Texas
A misfire judgement is based on a lack of acceleration of the crankshaft, via the CKP signal, during the combustion stroke of a particular cylinder.
The ECM uses cam sensor signal, to know what cylinder should have just fired and didn't(there is no such thing as 180 out with the ignition system, as it sparks each cylinder on both compression and exhaust). This means that an issue with the reluctor on the flywheel can cause a misfire fault as well, but would do so with two cylinders at a time. Makes it easy, right?
However, the two cylinders that would be flagged would be two opposite in firing order, 1-6 2-3 4-7 5-8, this is also the set up for the waste spark/coil sharing. A bad coil(as in electrically bad, not physical damage to a HT lead pin) will always cause misfires on two of the cylinders above.
Also, an issue caused by the CKP reading, would effect spark, which is what you would lose for a bad coil too. Luckily, you 'should' get a code for a CKP error, if it is losing its signal.
The ECM uses cam sensor signal, to know what cylinder should have just fired and didn't(there is no such thing as 180 out with the ignition system, as it sparks each cylinder on both compression and exhaust). This means that an issue with the reluctor on the flywheel can cause a misfire fault as well, but would do so with two cylinders at a time. Makes it easy, right?
However, the two cylinders that would be flagged would be two opposite in firing order, 1-6 2-3 4-7 5-8, this is also the set up for the waste spark/coil sharing. A bad coil(as in electrically bad, not physical damage to a HT lead pin) will always cause misfires on two of the cylinders above.
Also, an issue caused by the CKP reading, would effect spark, which is what you would lose for a bad coil too. Luckily, you 'should' get a code for a CKP error, if it is losing its signal.
Rock Crawling
Joined: Mar 2013
Posts: 452
Likes: 26
From: Oregon, north of Salem
Totally agree... the liners really can't slip much anyway like in the bad old days. There is an excellent write up on cracks/liners somewhere (they guy even cut a cylinder/block in half to illustrate the point, if memory serves). I was speaking way too short about those matters... maybe because I am afraid that I have it myself (after replacing the HG) to avoid bad juju, and the cost of new/flanged liners and the machining that has to be done to place them is PROHIBITVE in my part of the world (150 per cylinder for machining alone, plus cost of liners and whatever else pops up). The cracks can appear in the cylinder walls and around the location of head bolts, and visual inspection is not definitive. Sorry; your post is much more thoughtful, and correct, than mine. However, again wanting to avoid bad juju but pressing on anyway, I think worn rings (as a cause of low compression) can cause a misfire code. At least, that was an issue for my buddy in his Disco II.
Thank you for the positive response to my post. However, when you say
"I think worn rings (as a cause of low compression) can cause a misfire code" I must say that if you are correct on this point, the rings must have been unbelievably worn, enough to contaminate the plugs with enough oil to effectively "kill" the plug, causing it to misfire----in working on Rovers since the mid 1960s, I have never seen rings so worn---this isn't to say it couldn't happen though.
When you say " the liners really can't slip much anyway like in the bad old days," you are 100% accurate, because once Rover started to cast shoulders in blocks, at base of each cylinder sleeve, they effectively made it impossible for liners to slip or move downward at all----all you need to prove this, is to look at the substantial aluminum shoulders, clearly visible, once the oil pan is off. The liners sit on these shoulders. However, leave it up to some Rover factory workers to screw a good thing up, wouldn't you know it, SOME cylinder liners were not pressed fully down onto these shoulders, allowing around 1/8" gap, or so, for them to slip down at least that much. So, only those with such faulty workmanship can, and do, slip, especially due to engine overheating, that cracks the walls behind liners, that frees up the liners, that causes their slipping.
Last edited by earlyrover; Jan 18, 2014 at 03:46 PM.
Camel Trophy
Joined: Nov 2012
Posts: 3,717
Likes: 248
From: Longview, Texas
EarlyRover, you are definitely one of the more knowledgeable people in these forums who takes extreme care in his posts. I hope you'll take the time to respond to my questions when I have them, and I have them all of the time.
Best,
Charlie V
Best,
Charlie V
Camel Trophy
Joined: Nov 2012
Posts: 3,717
Likes: 248
From: Longview, Texas
I always thought that was baloney. It isn't.
Thread Starter
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Rock Crawling
Joined: Nov 2009
Posts: 307
Likes: 11
Yes sir, a coil puts out a LOT of juice, so arcing can happen.
I'm still only showing a P0307 misfire, and no other codes for my O2's or such. With a bit of good juju from the rover-god totem pole I carved in the yard from an entire tree, the plugs wires and seafoam will knock this out.
The P1319 went away after I filled the tank and cleared the computer. The PO was some idiot broke girl who had no gas in the tank...I swear, the more 20-somethings I meet the less I want to have kids..they're all such helpless morons....*sorry, rant over*
Results soon.
- dc
I'm still only showing a P0307 misfire, and no other codes for my O2's or such. With a bit of good juju from the rover-god totem pole I carved in the yard from an entire tree, the plugs wires and seafoam will knock this out.
The P1319 went away after I filled the tank and cleared the computer. The PO was some idiot broke girl who had no gas in the tank...I swear, the more 20-somethings I meet the less I want to have kids..they're all such helpless morons....*sorry, rant over*
Results soon.
- dc
