Vacuum gauge tuning
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Oct 2001
Posts: 20,506
Likes: 565
From: Bend, Oregon
James wrote:
[quote] Anyone have an opinion on the best source for vacuum when doing a little gauge-based diagnosis?
<hr></blockquote>
I guess it depends on what you are trying to diagnose. If you are looking for ignition timing, valve timing, or plugged exhaust symptoms, attach the gauge to the full-port vacuum from the manifold. An easy place to find this on my car is at the hose that runs from the intake plenum to the solenoid for the flappy.
Another coomn spot for non-flappy cars is upstream of the check valve, where the hose runs down to the "accumulator" in the left fenderwell rear. I think the 'T' is by the brake booster. In the end, just about any non-ported source is OK, so long as there are no solenoids or check valves between the gauge and the engine.
HTH!
[quote] Anyone have an opinion on the best source for vacuum when doing a little gauge-based diagnosis?
<hr></blockquote>
I guess it depends on what you are trying to diagnose. If you are looking for ignition timing, valve timing, or plugged exhaust symptoms, attach the gauge to the full-port vacuum from the manifold. An easy place to find this on my car is at the hose that runs from the intake plenum to the solenoid for the flappy.
Another coomn spot for non-flappy cars is upstream of the check valve, where the hose runs down to the "accumulator" in the left fenderwell rear. I think the 'T' is by the brake booster. In the end, just about any non-ported source is OK, so long as there are no solenoids or check valves between the gauge and the engine.
HTH!
Thread Starter
Rennlist Member
Joined: Aug 2001
Posts: 502
Likes: 0
Helps a lot; thanks.
You don't want to know what I'm hunting for...it's so unpleasant that I don't want to mention it in public.
Put it this way. I also will be doing a leakdown to see if my radiator is being pressurized...
It's been one thing after another lately.
You don't want to know what I'm hunting for...it's so unpleasant that I don't want to mention it in public.
Put it this way. I also will be doing a leakdown to see if my radiator is being pressurized...
It's been one thing after another lately.
Rennlist Member
Rennlist Site Sponsor
Joined: Jun 2001
Posts: 6,469
Likes: 13
From: Ball Ground, GA
You can make a quick and dirty tester to check for a blown head gasket.
Get an old spark plug, cut the ridge that holds the ceramic in and remove the ceramic center. Attach a piece of metal tubing long enough to get out of the plug wells, and attach a male air hose fitting. You can buy a plug adapter with an air hose fitting already made, but it may not fit down in the 928's plug wells.
Remove the plug in the suspect cylinder, use a two-foot wooden dowel as an indicator and turn the crank to put the piston on TDC. Remove the cooling system cap. Install the tester, hook to an air compressor and put air pressure in the cylinder.
If air leaks into the cooling system and bubbles up in the tank, you have a blown gasket or a cracked head.
Get an old spark plug, cut the ridge that holds the ceramic in and remove the ceramic center. Attach a piece of metal tubing long enough to get out of the plug wells, and attach a male air hose fitting. You can buy a plug adapter with an air hose fitting already made, but it may not fit down in the 928's plug wells.
Remove the plug in the suspect cylinder, use a two-foot wooden dowel as an indicator and turn the crank to put the piston on TDC. Remove the cooling system cap. Install the tester, hook to an air compressor and put air pressure in the cylinder.
If air leaks into the cooling system and bubbles up in the tank, you have a blown gasket or a cracked head.
Trending Topics
Thread Starter
Rennlist Member
Joined: Aug 2001
Posts: 502
Likes: 0
Thank you, Wally.
Randy, I think the inner-tube trick is to check for vacuum leaks - the tube goes over the intake throat.
Is this what you speak of?
<a href="http://ourworld.compuserve.com/homepages/nichols/tip367.htm" target="_blank">http://ourworld.compuserve.com/homepages/nichols/tip367.htm</a>
Randy, I think the inner-tube trick is to check for vacuum leaks - the tube goes over the intake throat.
Is this what you speak of?
<a href="http://ourworld.compuserve.com/homepages/nichols/tip367.htm" target="_blank">http://ourworld.compuserve.com/homepages/nichols/tip367.htm</a>
Rennlist Stories
The Best Porsche Posts for Porsche Enthusiasts
9 Features and Characteristics That Only Porsche People Understand
Verdad Gallardo
I've Written 500 Rennlist Articles: Here's How Porsche Has Changed Along the Way
Joe Kucinski
10 Most Unnecessary Porsches Ever Built (And Why We Love Them)
Verdad Gallardo
Porsche 911 GT3 S/C vs 718 Spyder RS: 10 Categories, One Winner
Joe Kucinski
This Builder Is Turning Heads With Its Slantnose 911 Creation
Verdad Gallardo
Porsche 911 GT3 Artisan Edition Pays Homage to Japanese Culture
Verdad Gallardo
Porsche Reveals Coupe Variant of the Electric Cayenne With a Fresh Look
Verdad Gallardo
10 Porsche Colors That Have More Personality Than Most People
Verdad Gallardo
Guntherwerks' Final Speedster Creation Is the Ultimate Porsche Restomod
Verdad Gallardo
Thread Starter
Rennlist Member
Joined: Aug 2001
Posts: 502
Likes: 0
Oh, the usual...although as of yet all unconfirmed.
Coolant in the oil, foamy crap in the oil breather, miss on the #5 cylinder, all following a recent overheat. Thought I caught it in time, but maybe not.
I hope I'm just being precautionary, because my baby has REALLY been trying the extent of my love lately.
Coolant in the oil, foamy crap in the oil breather, miss on the #5 cylinder, all following a recent overheat. Thought I caught it in time, but maybe not.
I hope I'm just being precautionary, because my baby has REALLY been trying the extent of my love lately.
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Jun 2000
Posts: 40,491
Likes: 140
From: Insane Diego, California
No, the procedure I referenced was to use the bicycle tube on the cooling loop - perhaps it was for checking a leaking autotrans cooling system, rather than a leaking head.
Help me out Wally...
Help me out Wally...
Rennlist Member
Rennlist Site Sponsor
Joined: Jun 2001
Posts: 6,469
Likes: 13
From: Ball Ground, GA
Oil in the coolant and coolant in the oil may be a head gasket, or may be a leaking oil cooler in the radiator side tank.
The tester that Randy is referencing is a motorcycle inner tube (hopefully free or very cheap from a motorcycle shop, since you can use a blown tube) that is cut, and the ends placed on the radiator coolant connectors. You can then pump the tube and the radiator up thru the tube valve stem, putting gentle air pressure on the radiator.
By laying the radiator face down and filling the oil cooler with a solvent, or oil, you can then check for bubbles in the cooler connections.
If there is a leak in the cooler, oil will be forced into the coolant while the engine is running (75 psi oil, 15 psi coolant), and coolant will be forced into the oil immediately after shut-down of a warm engine (o psi oil, 15 psi coolant).
That won't make #5 cylinder miss, though. Air pressure in the cylinder is probably the surest test.
Since I just very stupidly overheated the engine in our Trooper, and now have 70 psi in one cylinder - and between 10 and 30 in the other three - I can sympathize. I think that mine will be cheaper to repair!
The tester that Randy is referencing is a motorcycle inner tube (hopefully free or very cheap from a motorcycle shop, since you can use a blown tube) that is cut, and the ends placed on the radiator coolant connectors. You can then pump the tube and the radiator up thru the tube valve stem, putting gentle air pressure on the radiator.
By laying the radiator face down and filling the oil cooler with a solvent, or oil, you can then check for bubbles in the cooler connections.
If there is a leak in the cooler, oil will be forced into the coolant while the engine is running (75 psi oil, 15 psi coolant), and coolant will be forced into the oil immediately after shut-down of a warm engine (o psi oil, 15 psi coolant).
That won't make #5 cylinder miss, though. Air pressure in the cylinder is probably the surest test.
Since I just very stupidly overheated the engine in our Trooper, and now have 70 psi in one cylinder - and between 10 and 30 in the other three - I can sympathize. I think that mine will be cheaper to repair!