Alfa Romeo Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
132 Posts
Discussion Starter #1
After the valve replacement everything was put back in and timed. The car is hard to start and ones started runs rough and runs on the rear 3 cylinders only. All the fronts are inactive. Fuel is okay checked injectors. coil resistance is okay although didn't check power. What could it be? Maybe switched cams exhaust and intake as I had trouble differentiating them? But the markings both lined up in either position even if the cams were switched. Could this be tha cause? Or bad ignitor? I didn't switch the harnesses yet. Please help.
 

·
Registered
Joined
·
1,765 Posts
After the valve replacement everything was put back in and timed. The car is hard to start and ones started runs rough and runs on the rear 3 cylinders only. All the fronts are inactive. Fuel is okay checked injectors. coil resistance is okay although didn't check power. What could it be? Maybe switched cams exhaust and intake as I had trouble differentiating them? But the markings both lined up in either position even if the cams were switched. Could this be tha cause? Or bad ignitor? I didn't switch the harnesses yet. Please help.
Presumably the spark plug leads are all in the correct places? Or does that engine have coil packs? (did you mean coil resistance or resistances?;)) I'm not familiar with the LS model.

Then again, it must be a 24-valve as you mentioned switching intake and exhaust cams - this wouldn't be possible on the 12V.

Perhaps (and I'm not 100% sure) a good way to check might be to test for compression in the cylinders at the right times. I guess that you would start from cylinder 1 and turn the engine with something covering the spark plug hole, then when you have compression you could check that the timing marks align (ignition for No.1 cylinder, I believe) and then turn the crankshaft through about 60 degrees, testing next for compression on cylinder 4 (firing order is 1-4-2-5-3-6).

I can't find a description of the cylinder numbering anywhere, so hopefully the V6 follows the usual Italian tradition of having a number on the cylinder heads near each spark plug hole.

If the front bank camshafts were wrong, I think the compressions would be in the wrong places - wouldn't they?

Probably Alfisto Steve will have a method of ID-ing the camshafts, and then you'll be away laughing. But that possible camshaft swap does sound like a cause to me.

Cheers,
-Alex
 

·
Registered
Joined
·
132 Posts
Discussion Starter #3
The problem is that the part numbers been grinded off by the factory and there is no way to tell which is which. Both cams when switched around still align to proper timing marks. I heard a lot of italian cars have the same intake and exhaust cams? When I did compression check in the front banks I was getting 90,16 could this be also because the battery was getting weak?
 

·
Registered
Joined
·
4,501 Posts
...The car is hard to start and ones started runs rough and runs on the rear 3 cylinders only...
1) Lucky you! :D With this type of problem, it is almost ALWAYS the rear bank that has a problem (so now you have to go off and on, off and on with that intake plenum, AFM, T-body etc etc. each time between tests. :mad:)

2) As far as compression; those are bad numbers! I don't mind them being low (since it was a cold-test I would assume), but they should be pretty even across all cylinders! Also, are you taking your checks with the THROTTLE PULLED OPEN!? Hold it open while cranking for EACH cylinder and then compare the numbers!

3) Sure sounds like one of the two ignition-modules bolted down just to the right of the air-box (at the front of the engine-bay - just below the fan relays and the cruise-control unit), was somehow disturbed, or damaged or unplugged! Check the connections to those two - swap the two leads and see if the problem moves to the rear bank!

4) Assuming that you did a noid-light to each injector-lead to verify signal to each injector? Well, try swapping injectors to the rear bank and see if you maybe have clogged injectors after the rebuild on that bank!? (Should have had them all cleaned/reconditioned as part of this any way.)

5) Assuming that you have done a test-plug to each coil-pack to verify that you are getting spark-signal through to each plug. Well, same story here - new plugs (hard to believe that three of them go bad just like that, but I had a guy once rebuild a Datsun head and in the process of reinstalling the head, he had the plugs already in the head - while installing them the plug-gaps got smashed shut! (Harder with the hemi Alfa head - I know, but still...

6) Verify the numbers on each of the spark-plug leads (Assuming that they are all still semi-visible.)

7) Verify the numbers on each of the coil-pack leads (Assuming that they are all still semi-visible.)

8) Inlet and exhaust cams ARE different on this motor! However, inlets cams are the same - bank to bank. Exhausts are different bank to bank! Still, it IS possible to switch cams on these motors (all except for the right exhaust cam - rear bank exhaust - because it has the cam-angle sender signal-wheel on it!) Can't miss it. The marks may seem faint, but they are there! Some may say that you should use cam-locks - great! (If you have a set...)

Why would the marks be grinded off?

Even without cam-locks - call me once you have the front cam-cover off and I will tell you exactly where to look! There are those little stripes on the rear of each cam (factory "grab" marks during manufacturing...) Unfortunately, they look very similar to the actual timing marks for each cam - but once you SEE one of the actual marks on a cam, you will never miss them again!

Those marks line up with the head-surface on the INSIDE (between the cams) on each head... Once on the mark, compare each cam lobb's approximate position, to those pictured in the manual on the car-disc - they match!

Good luck,
JvR
425.941.4747
 

·
Registered
Joined
·
132 Posts
Discussion Starter #5
Well confirmed today the cams have been put in the reverse order. I will change it back tomorow crossing fingers it will run great. Thanks John for all the help
 

·
Registered
Joined
·
3,506 Posts
Gabor,
The 12V engines, and I presume the 24V are the same in this regard, are set up so that the pistons run with pairs in the same TDC/BDC orientation. The firing order is 1-4-2-5-3-6, so 1/5 run 180 degrees out in cam timing and the same for 3/4 and 2/6. You should be able to check the cam lobes with the valve covers off and verify that the intake lobes for these pairs are 180 degrees out from each other: 1 is 180 degrees out from 5, and so forth.

If you start with the crank/cams set so that #1 intake valve is full open, #5 intake should be opposite. A 120 degree crank angle change will put #4 intake at full open and #3 at full clearance. I hope this helps. I wanted to make sure I understood what was happening with the valves when I rebuilt the wife's engine, so I thought this through and satisfied myself that it was correct. If you compare this against the absolute crank reference for TDC, it would be hard to go wrong.

Another thing I did was to rotate the engine manually to check for interferences, and the first thing I did after getting the engine back into the bay and connected was to do a cold and pre run-in compression check. I got numbers near 170 and haven't repeated since the engine has been run in.

Michael
 

·
Registered
Joined
·
132 Posts
Discussion Starter #7
Michael,
Switched the cams around started right up. What a difference. There is still have some minor misfires at idle but that might due to some leaky boots and dirty injectors. It wouldn'y suprise me the car was sitting for so long. Actually the intake and exhaust cams are the same spec just the timing marks and maybe lobe positions might be different. Cam lobe height and width are the same according to the manual. Even with the cams reversed I didn't have any valve clearence issues just that the car run like it was on 3 cylinders and was hard to start. Well now I have to work on the roof, brakes, interior and lots of other things.
Thanks for all the help John, Michael. I'm happy like a fat kid in a chocolate factory.

P.S. The Full stebro sounds so BAAAAD it really brings the 24V alive.
 
1 - 7 of 7 Posts
Top