Ever seen a skimmed head cause cam timing/correlation fault?
Discussion
I recently built a forged engine for my 2001 Audi A3 1.8t and since fitting it, it keeps throwing a cam timing correlation fault code (17748)...
It will initially clear, and then consistently come back after about 10 seconds of running. Which is what you'd expect to see from the timing being a tooth out, however all timing marks line up 100%. Which anyone who had worked on these engines a lot is odd in it's self, as the cam mark will often sit a bit forward.
I've tried bloody everything! . .
-Cam sensors
-crank sensors
-chain tensioner/chain
-belt tensioner (was an ebay special originally)
-Oil pressure
-Manually TDC'd to check marks
-Counted chain links inbetween cams
-Checked reluctor ring orientation
If it was a wiring issue I'd expect a different code, and I would expect it to come back straight away...
The donor engine I used was re-manufactured by Ivor Searle in 2009, when I put the engine together I noticed it looked like the head had been fairly heavily skimmed as the depth of the combustion chamber at it's shallowest point (by the middle inlet valve for those of you familiar) was visibly shallower... Thinking nothing of it the engine went together
No doubt the block had been decked as well... obviously the more you take out in-between the cam and crank will be taken up by the belt tensioner and slightly bring the cam back ans/or the crank forward, which ever way you want to look at it!
Could this really throw a timing fault though? . .
Ive got a few mates with some proper diagnostics kits so at some point I'm going to take it to them and see if we can work out what the ECU is seeing. But I'd be interested to know your thoughts and experiences first guys!
Thanks in advance and sorry for the lengthy post, just wanted to get the full story across!
It will initially clear, and then consistently come back after about 10 seconds of running. Which is what you'd expect to see from the timing being a tooth out, however all timing marks line up 100%. Which anyone who had worked on these engines a lot is odd in it's self, as the cam mark will often sit a bit forward.
I've tried bloody everything! . .
-Cam sensors
-crank sensors
-chain tensioner/chain
-belt tensioner (was an ebay special originally)
-Oil pressure
-Manually TDC'd to check marks
-Counted chain links inbetween cams
-Checked reluctor ring orientation
If it was a wiring issue I'd expect a different code, and I would expect it to come back straight away...
The donor engine I used was re-manufactured by Ivor Searle in 2009, when I put the engine together I noticed it looked like the head had been fairly heavily skimmed as the depth of the combustion chamber at it's shallowest point (by the middle inlet valve for those of you familiar) was visibly shallower... Thinking nothing of it the engine went together
No doubt the block had been decked as well... obviously the more you take out in-between the cam and crank will be taken up by the belt tensioner and slightly bring the cam back ans/or the crank forward, which ever way you want to look at it!
Could this really throw a timing fault though? . .
Ive got a few mates with some proper diagnostics kits so at some point I'm going to take it to them and see if we can work out what the ECU is seeing. But I'd be interested to know your thoughts and experiences first guys!
Thanks in advance and sorry for the lengthy post, just wanted to get the full story across!
bearman68 said:
The problem is of course it's almost impossible to get hold of a known good one, though you would expect 'edges' to align exactly.
One thing I have done is to check the spark position with regard to compression. I don't know if it's a valid test, but the logic seems to work.
Stop the engine starting, buy pulling the injectors off or something. Rig up a channel to an ammeter, and monitor starter motor current. On the second channel, monitor the spark event. In my experience, on crank, the spark event should occur on max compression. Even small deviation means the timing is out.
I have seen fiat engines in particular throw these codes for very little reason. (They can be mapped out if you really really want).
What, a known good engine to compare to? . . Surely that's just a running 1.8t that's not throwing a timing code?One thing I have done is to check the spark position with regard to compression. I don't know if it's a valid test, but the logic seems to work.
Stop the engine starting, buy pulling the injectors off or something. Rig up a channel to an ammeter, and monitor starter motor current. On the second channel, monitor the spark event. In my experience, on crank, the spark event should occur on max compression. Even small deviation means the timing is out.
I have seen fiat engines in particular throw these codes for very little reason. (They can be mapped out if you really really want).
And as for a decent scope, my old boss has 10 grands worth of snap on diagnostics with a built in scope and stuff... I'm sure he wont mind me borrowing it, just gotta remember how to use the thing!? lol
With regards to the head it's self and the proper skimming procedure, you'd like to think a company like Ivor Searle would get that right!? . . And I'm not so concerned you can't tell us this trick as I have no idea what an avocado is anyway, sounds way to technical for me!
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