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Ignition timing [Expired Topic]

6144 Views 20 Replies 3 Participants Last post by  ChevyFan
Hi everybody,

I'm peter from Belgium and I like to ask a question about my Suburban.
I want to adjust the ignition timing but I don't know how many degrees BTDC.
In the books I have, they say check emissions label, but there isn’t any on my Suburban. :(
It’s a Suburban 1993 350 V8 TBI

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Hi Peter, welcome to the club!
I'm fairly certain that the timing for your engine is 4Deg BTDC.
There should actually be a label on your air cleaner that tells you the details for your ignition timing.

Why do you need to adjust your timing?
I'm searching for an answer why my Suburban has no power, and the fuel consumption is outrages 38 L / 100 KM I don’t know it in MPG.

I can't find the label anywhere, I think it's removed

That works out to 10Gal / 62Miles (for those of us on the SAE, so we can relate)
Which is about 6 miles to the gallon, or 2.63 km per Litre.


Can you give us some more details?
How many km on suburban?
How long since last tuneup?
Where is the loss of power? (Light accelleration, heavy accelleration, throughout entire throttle)
Does the engine idle smooth or roughly?
Oversized tires/tyres?
Any vehicle mods, or completely factory?

There aren’t any modifications made, except removal of the catalyst.
The tire size is a little bit taller than stock, but not too much. :roll:
For the rest is everything stock on the engine.
It has 160000 miles on it
The automatic gearbox has an electronic shiftimprover.

Yesterday my check engine light came one giving me code 44 (lean exhaust)
How is this possible with this high usage of fuel?
You might want to try changing out the O2 sensor (this is a single wire sensor, and the wire is usually black on that model year). it's located just past the Y in the exhaust pipe. If it's the factory sensor, it's going to be tough to get out of there. The sensor itself doesn't cost much since it's not a heated unit. So it's a fairly inexpensive place to start, and probably the only thing that's wrong with it.

Normally they make a special socket with a slot up the side for those kind of sensors, but if you have trouble getting it out, you might have better luck with a small pipe wrench, but definately use the socket to put the new one in.
Don't forget to put anti-sieze on the new sensor for the next time. 8)

Reply back with your reults.

Good luck! :D
Ok I will try that

Thanks for the info :wink:
I had an O2 sensor go out 3 years ago in a diff vehicle and it was amazing how it affected gas mileage. You would think the engineers would understand that these things go out and they would compensate better for the lack of information coming back into the engine!

Anyhow, let us know how that works out will you?
Actually the newer ones, I think it's '96 and up (I'll check the books) have more than one O2 sensor. So it's not as bad if one fails, but it still affects mileage.
Don't most have one per header?
Exactly on the '96 and newer it's one per header, but they're in the "Y pipe"
Peter, I asked if there were any modifications made....Propane is a big :mrgreen:
From what I understand you should expect a lower km/litre when using propane on this engine.
Did you determine if this poor engine performance was due to the intake manifold gasket, or something else.

Does your impco system even use the feedback computer, and is it running off of a signal from the O2 sensor?

This poor engine performance could be a whole new set of problems that we never would have discussed if we never knew you were running propane.
Hi Patrick,

The problems that I have are also on gasoline.
And when it runs bad on gasoline it also runs bad on propane.

You call propane a big modification :mrgreen: , around here it’s a normal thing due to the high taxes on fuel.

When I run on propane everything from the motor management is disabled that’s normal for an Impco installation it’s not the best way to go I understand that.
I didn't think propane was so common over there. I can see why it would be. It's so much cleaner.
Was the problem/ poor performance due to the coolant leak in the intake manifold?
After fixing the leak the performance is a little bit improved.
It’s a strange behaviour one time the suburban is slow the other time fast.
Maybe I am looking in the wrong place; it could be the automatic transmission. I don’t know.
Is it like that with both fuels?
When you say that it's slow sometimes and fast at other times. Is this noticable? I had this happen before from an intake manifold leak on an old 350 4-bolt. Ended up leading to a cracked block. :-(
That was a 1973 350 4-bolt police special that I had too. :-(
@TrailLeadr The performance is better on petrol, but that’s normal you can say it’s on both fuels the same problem it can run great for a couple of days and then it’s back to pour performance. :(

@Steve I already changed the joint from the intake manifold there was a little improvement there. :wink:

The reason that I am thinking on the transmission is because when I hit the gas the rpm goes up for about 600 rpm before the transmission kicks in. Maybe that’s normal I don’t know it’s my first Suburban.
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