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Old 05-27-2009, 08:02 PM
 
Location: Grosse Ile Michigan
30,255 posts, read 74,453,333 times
Reputation: 38281

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We have a 2002 Chevy Express Van that we had in to a shop for some undrealted issues. The mechanic called and said that he found the distributor tobe 40 degrees off. He said that the computer (OBDII I think it is called) corrects the timing but cannot correct 40 degrees.

I am curious. How can it be that far off and the car still running fine? Could it be intentionally off? Is he likely just wrong?

Thanks.
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Old 05-27-2009, 08:40 PM
 
Location: Poway, CA
2,698 posts, read 11,481,365 times
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don't quote me, but i don't think your van even has a distributor. i'm almost positive that, by 2002, GM engines all used a computer-controlled ignition system.

but to answer your question, if a car were to run at all at 40 degress off, it would run like absolute hell. you would have noticed.

sounds to me like you need a new mechanic.

Mike
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Old 05-27-2009, 08:53 PM
 
3,144 posts, read 8,221,737 times
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Quote:
Originally Posted by whiteboyslo View Post
don't quote me, but i don't think your van even has a distributor. i'm almost positive that, by 2002, GM engines all used a computer-controlled ignition system.

but to answer your question, if a car were to run at all at 40 degress off, it would run like absolute hell. you would have noticed.

sounds to me like you need a new mechanic.

Mike
Just looked up all the engines available for his van and they all utilize cam driven distributors, except for the diesel of course. I believe your thinking of Ford.

As for the 40 degree ignition timing... quite impossible for the van to run, im sorry but that mechanic has lost his marbles or just being the typical lying scumbag. Assuming its a V8 (which it most likely is) each contact in the distributor is only 45 degrees apart... so if its advanced 40 degrees there is a plug trying to ignite a cylinder still on the intake downstroke.... retarded 40 degrees theres a plug trying to ignite a cylinder at the tail end of its combustion downstroke... nonsense.
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Old 05-27-2009, 08:59 PM
 
Location: louisiana
139 posts, read 995,298 times
Reputation: 89
Could it have possibly been 4 degrees off and not 40? just a thought.
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Old 05-27-2009, 09:00 PM
 
Location: H-town, TX.
3,503 posts, read 6,955,247 times
Reputation: 2232
Nah-uh.

Those vans still had the 2nd Gen SBCs (305/350) at that time. Still had a dizzy under the hood.

Just wondering what made him come to that conclusion. Did he pull codes or something or is this a random part-swapping drill in the making?
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Old 05-27-2009, 09:06 PM
 
Location: I think my user name clarifies that.
8,292 posts, read 25,496,682 times
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Quote:
Originally Posted by Coldjensens View Post
We have a 2002 Chevy Express Van that we had in to a shop for some undrealted issues. The mechanic called and said that he found the distributor tobe 40 degrees off. He said that the computer (OBDII I think it is called) corrects the timing but cannot correct 40 degrees.

I am curious. How can it be that far off and the car still running fine? Could it be intentionally off? Is he likely just wrong?

Thanks.
It can't be 40 degrees off and still be running.

Either you misunderstood something, or he's full of crap. I hope it's that you're misunderstanding something he said.
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Old 05-27-2009, 09:12 PM
 
Location: Michigan--good on the rocks
2,544 posts, read 4,059,484 times
Reputation: 1956
Don't these install so that they are either on or 180 off? I might just be thinking too old school. 40 deg. off doesn't make any sense to me.

You most definitely would have noticed it.
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Old 05-27-2009, 09:18 PM
 
3,144 posts, read 8,221,737 times
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Quote:
Originally Posted by Drilco View Post
Could it have possibly been 4 degrees off and not 40? just a thought.
4 degrees BTDC is common OEM timing specs, certainly not an issue for the computer.
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Old 05-28-2009, 09:05 AM
 
Location: Grosse Ile Michigan
30,255 posts, read 74,453,333 times
Reputation: 38281
He said the the computer cna correct up to 35 degrees off, but at 40 degrees off the computer cannot correct it. I asked why the car seemed ot be running fine and he said that the computer must be correcting it enough to not be noticable. Maybe I should talk to the dealer (if they have not been closed by tomorrow).

I do not know why he was even looking at this. We brought it in to fix the AC, the window switches and an oil change.

Another odd thing I asked him to look at the transmission because it pauses before going into reverse. He said that may be caused by the distributor being off.

I got a bit suspicious at that. However this mechanic was recommended to us by four or five different people.
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Old 05-28-2009, 12:21 PM
 
Location: Eastern Washington
16,201 posts, read 52,966,362 times
Reputation: 16376
Gents,

It's important to distinguish between crankshaft degrees and distributor degrees. Although 40 degrees is a lot. Remember though in a 4-stroke engine you have 720 degrees per complete cycle (2 complete revolutions). Up to 40 degrees of total timing advance (crankshaft) is not uncommon for old-school Chevy small-block V-8's IIRC. Distributor degrees are half crankshaft.

In general computer-controlled engines with distributors do use the base timing of the distributor as a starting point for all their calculations and assume it's correct.

The 3S-FE in the Camry is one of these. When I had the head off to do a head gasket replacement, discovered that the engine's timing marks were about 5 degrees off, so on re-assembly set the timing 5 degrees more advanced, made a difference in how the car runs.
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