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!
stevieturbo said:
Scope crank/cam and compare to a known good setup to see how far it is actually out
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).
The cam timing error vs head or block skim depends on the size of the pulleys. For an average engine every 1mm off the head or block retards the cam timing by 2 crank degrees. The larger the pulleys (more teeth) the smaller the error.
How many degrees it takes to throw a fault code I have no idea.
How many degrees it takes to throw a fault code I have no idea.
BTW, the usual reason for skimming a head an abnormal amount is because it was warped after overheating. They nearly always go concave on the gasket face and convex on the top face. However this still leaves the top of the head and the cam bearings bent. The correct procedure is to straighten the head first as much as possible and then skim as little as possible to get a flat gasket face. If you lay the cams in their bearings and the cams rock about the centre bearing then the head is unacceptably warped. The cams will be clamped down bent and have to oscillate every time they rotate. This is a bad thing n'kay.
There's a simple trick to straighten an aluminium head without damaging it with a length of 2x4 wood, a big hammer and an avocado, or a banana if you don't have an avocado. I'm sworn not to reveal it though.
There's a simple trick to straighten an aluminium head without damaging it with a length of 2x4 wood, a big hammer and an avocado, or a banana if you don't have an avocado. I'm sworn not to reveal it though.
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!
Does the early 1.8T have VVT? I can't remember now? Pretty sure the later 225 engines do, and any incorrect assy or VVT control issue (including blocked oil ways etc) can lead to the cam position not being at target and set a code (i would expect a "cam position error" code to be set, but maybe that is what you are seeing?)
Max_Torque said:
PS, pretty sure the 1.8T VVT is a "chain slack movement" system, that effectively moves the intake cam forwards or backwards by moving the "side" on which the crosshead chain slack is taken up by the tensioner slides/guides
Yep. It's only for warm up emissions and not full time cam phasing like the R32 engine.SuperchargedVR6 said:
Max_Torque said:
PS, pretty sure the 1.8T VVT is a "chain slack movement" system, that effectively moves the intake cam forwards or backwards by moving the "side" on which the crosshead chain slack is taken up by the tensioner slides/guides
Yep. It's only for warm up emissions and not full time cam phasing like the R32 engine.Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff