Xu7 Bad Idle After Head Rebuild

[tompaltridge 0]

I gather the XU7JP is similar to the GTi engines so hopefully someone might know what's wrong.

 

The in-laws' Berlingo snapped its belt a couple of weeks ago and their local garage quoted far in excess of the car's value to repair.

I offered to do it because it would save all of the labour cost.

Now at this point I don't know/remember exactly how well it used to drive/idle before the damage (I've only been in the car a few times), it has 255k on the clock so is no spring chicken. They've owned it since new: 1998.

 

I removed the head, saw one bent valve and left them to sort out someone to rebuild it. They duly did and the head came back repaired (one new valve, the 7 others were fine) and lightly skimmed.

I timed up the crank and camshaft, fitted a new HG and reassembled the whole thing.

 

I disconnected the injectors and cranked on the starter for total of ~20 seconds to get some oil to the camshaft.

Then, fired it up.

 

It idled fine and sounded fine. No tapping whatsoever.

 

Went back out to give it a test run later and it would often cut out on idle if left alone. Blipping the throttle kept it alive. Holding the throttle kept it alive. Reminded me of my 205, years ago.

 

Additionally, the idle is now uneven and 'chugging' a bit. It's rthymic and regular, not hunting. The tacho stays still, not fluctuating.

It sounds almost like it's 'missing' (I hate that word but it gets the message across hopefully)/running on 3 cylinders, but I don't think it is.

I did get it to behave eventually and took it for a ~10-15 mile test run. It pulled away perfectly smoothly in first gear and revs cleanly through the gears. No apparent flat spots or uneven power delivery. Sounds smooth. Assume not running on 3 cylinders...

 

I checked the timing about 6-7 times in total at various stages of the rebuild because I'm anal about it. Each time both locking pins were able to be inserted fully in the crank and cam.

As far as I'm aware I reconnected every hose and electrical connector that came off.

 

 

So, thoughts?

Edited December 4, 2013 by tompaltridge

[Tom Fenton 1,542]

Compression test first of all.

[Anthony 1,003]

As said, compression test first, and then check for air leaks.

 

Did you check the valve clearances when you were rebuilding the head? If the seats were recut then that would throw the clearances out, as normally would a replacement valve

[tompaltridge 0]

I didn't rebuild the head, that was taken care of by a separate garage/engineering place. I'll see if I can get hold of a compression tester.

Also thought about air leaks, as you said. Most likely to be at the inlet manifold I assume?

[calvinhorse 870]

Sound exactly like the girlfriends 306.

 

I've never got to the bottom of it.

 

It's had 2 new lambdas, icv, plugs, coil but never a maf/map sensor.

 

It runs perfect and doesn't use excess fuel but chug chug chugs on tickover.

[Jolly Green Monster 51 1 Cars]

Would check cambelts not jumped also.

[joshsnoad 2]

Sounds like timing is 1 tooth out to me, especially if is fine when cold/ fast idle and only mucks around when warm

[welshpug 1,661]

just a thought, is the crank pulley on these a solid metal one or a two part like a gti6?

[tompaltridge 0]

Apologies Mei, I forget to check 'drivers as often! I was thinking about the crank pulley before I did the job and was relieved to find that it's solid steel, unlike the 6.

I've just been out for another test drive in it and it's still chugging on tickover. Worse, it now seems lacking in power at low revs when it didn't seem to a couple of weeks ago when I drove it. Whipping out the HT leads whilst idling didn't seem to affect the already bad idle, bizarrely. The leads did ground though so I assume the spark supply is fine. There is some mayo under the oil filler cap but there was mayo under it before any work started too: 250k and mainly v short journeys over the last few years. Old gasket was in a bad way but didn't seem breached at any point.

 

The in-laws will take it to the head-repair guy to check over, I suggested a compression test but I'm sure the guy will do that anyway.

Really hoping that it isn't a missed bent valve or shim issue.

[tompaltridge 0]

Ok I finally got a compression tester on it. Results from left to right (that's number 4 to 1, yeah?): 14.75, 14.75, 14, 14.5

So they are all within 1 BAR of each other and all seem nice and high although I don't know what the standard compression is...

Can I now rule out any belt valves, bad gasket seal, warped head, cracked anything?

 

I took each plug out in turn and watched as it sparked as the engine turned over, so I have 4 sparks.

Haven't got around to quadruple checking the timing pins just yet but that will be my next port of call.

 

A recap:

When started from cold it idles evenly for several seconds, then becomes progressively more lumpy. At low revs in any gear it lacks power and judders. This is more pronounced in higher gears (5th is unuseable). This problem becomes less pronounced when the engine is warm: certainly not solved but better, especially in 2nd gear.

 

Any further thoughts?