Can a vacuum issue cause unsteady base ignition timing? If not, what all can?

[Gremo87]

I know I'm not a probationary member anymore but there doesn't seem to be a forum for general engine questions.

My base ignition timing is very unsteady, constantly jumping from 5* BTDC to about 2 or 3 ATDC - so a 7-8 degree range. (timing pin grounded with Link)

I also have low vacuum at idle (around 12-13 in hg shown in Link from MAP sensor, 14-15 on boost gauge) and am having trouble finding the cause.

Outside of mechanical timing being off (doesn't look to be), can a vacuum leak cause base timing to be unsteady like that? Or would it remain constant if the issue was just a vacuum problem alone? (like FIAV, which I think is the only thing I haven't ruled out yet)

 

[pauleyman]

Doesnt look to be? How about verifying with 100 percent accuracy by taking the covers off.

 

[Gremo87]

Pauleyman the lower cover is the only thing not off and I'm planning on getting in there - I just haven't had time lately. I know for sure that everything lines up with the exception of the oil pump - that's the only thing I can't see but will this weekend.

In the meantime I'm trying to learn what I can about other possible causes of the issue.

 

[97 eclenger]

a bad knock sensor can. especially at wot. it'll pull timing till the ecu is happy. usually a bad knock sensor will have the plastic melted in the sensor. a vacuum leak will cause problems. run a boost leak test. if theres no boost leaks, look at the knock sensor. could also be something as stupid as the cam sensor being 180* out but thats not very likely

 

[Gremo87]

But could the knock sensor effect timing at idle with the timing pin grounded?
[Edit: Just checked Link and my knock sensor control is set for above 2200 rpm so doesn't look like that's what's causing my issue since it happens at idle] - but thanks anyways for the idea!

I've done many boost leak tests and have fixed all the tiny leaks I could find, but haven't ruled out the FIAV. But if a vacuum leak can't cause base timing (with pin grounded) to be unsteady, I won't pull the TB to close the FIAV because then my issue must lie somewhere else.

So really I'm just looking to find out if a vacuum leak can effect base timing. I wouldn't think it could...but want to confirm to help me narrow down my search for the cause of the issues I'm having.

 

[97 eclenger]

make sure your engine is mechanically in time. 1 tooth off is loss of power. 2 teeth is start of a misfire. 3 is misfire with bad performance. 4 is a no start

 

[dtdeg]

strange its jumping like that with pin grounded. Could it be the scope ? check timing on all gears

 

[Gremo87]

Yeah I'm planning on getting the lower timing cover off by the end of this weekend.

What's even stranger though is that I just checked base timing again last night (for probably the fourth time) and it wasn't jumping nearly as much. Just a handful of times over 30 seconds or so, compared to constantly jumping all the other times I've checked.

Gonna check spark plug wire position and see if maybe the #1 wire was too close to the #2 wire before, and needs to be moved just a lil more. Timing light is brand new.

 

[dtdeg]

is your rpms jumping maybe also ? i mean, is your base idle steady ?

 

[Gremo87]

It's not steady. It's set in Link at 850 but constantly wanders from 750ish to 1000ish. And if I ground the timing pin, I get idle surge. If I then ground the diagnostic pin, the car dies.

And BISS is set so that isc position is as close to 30 as possible. (ranges from about 27-33)

 

[dtdeg]

hmm stepps is good, but maybe still check the isc ? you can check the ohms from pin 1+2 ,3+4,5+6. left side of pins is 1t/m3. ohms should reed 30 ohms on a yellow /brown isc. the black should read like 40 or so.

 

[Gremo87]

Yep that's done, it checked out fine. I've done a lot of troubleshooting already, hence the vacuum question. (cause I have low idle vacuum) Planning on checking oil pump sprocket mark, doing a leakdown test once I make a tester, and ruling out the FIAV - all hopefully before this weekend is over.

 

[doubleclutch]

What did you find? I am having a similar problem.