[tamathumper]

Thanks for all the help! Just got back with some extra vacuum hose, so I'm going to replace that one piece and hook up my vacuum/pressure gauge to see what's up. I will also try all those tests. I'm first looking for no signal from the crank position sensor, considering a new one didn't make any change at all. I'll also test the <acronym title='throttle position sensor'>TPS</acronym>, thanks for that!



My intake manifold has never been off to my knowledge.



Re: the tester, I've got an analog one... <img src="/forum/images/smilies/968/blush.png" class="smilie" alt="" />



I don't have a Durametric, though.



I did find a couple drops of oil on my exhaust shield when I went back out to the garage. That could explain the hiss I was hearing near the exhaust manifold, but could not locate. It might have been a leak out from under the cam cover... which would also explain the smell/smoke every once in a while, maybe that's where the oil is weeping out just enough to get near the exhaust manifold once in a while, usually after long spells of sitting.

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[MB968]

[quote name='Cloud9...68' timestamp='1368899729' post='142868']

An old, analog voltmeter is MUCH, MUCH better at seeing intermittent jumps than a digital one, but who the heck has one of those.[/font][/size]

[/quote]



Some of us old guys do. I still have the one that my dad had. And, I regularly see these avaialble at estate sales (for cheap), where guys are turning in their toys. Watching the sweep of a needle can be a real plus for some tests.

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[tamathumper]

The Throttle Position Sensor sweeps smoothly between less than .5V and about 4V.

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[MB968]

Edit: Just getting ready to post this when I saw your above note.



Do you still have a hard to start condition; I'd kind of forgotten about that? If so, I don't think the <acronym title='throttle position sensor'>TPS</acronym> is likely. And, .5 volts at closed throttle seems reasonable for the DME to recognize as a closed throttle voltage. I would definitely check to see if the CPS signal is making it to the DME.

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[Lear35A]

You said you had a hiss towards the rear of the engine, exhaust side, that you couldn't locate ? There's a vacuum reservoir and various vacuum connections in the battery box. Have you checked there?

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[tamathumper]

The hard-to-start has only happened twice in the past several months, so it's unfortunately not a repeatable thing. We just cranked it a lot while I tested both sensors, and I verified that the crank position sensor (on the bell housing) is putting out good voltage on both sides of the connector, and the hall sender (at the cam end of things) is putting out good voltage while running as well, about 6V AC from the center wire when idling, and 3V DC from the center wire with the ignition on (and the proper 5V DC from the foremost wire with the ignition ON).



Regarding vacuum, yes, I did check in the battery area, the hiss is definitely in the area of the exhaust manifold (in front of the firewall). I've replaced the questionable piece of hose and everything I can get my hands on is snug and not leaking. I suspect the hiss was the camshaft cover, given the drop of oil I found on the heat shield afterwards.



I put my vacuum gauge on as many fittings as I could and got very different readings. I don't know what to expect, so my testing was probably not very scientific. I do recall however that at the throttle body, I got basically no reading at idle, at the heater control valve the same thing (car was cold so maybe that's why?), and I got about 15 psi (perhaps even more) at the fuel pressure regulator when revving the engine.

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[flash]

there is one connection there on the firewall that is a pain in the butt to get to.



you should see 17 inches of vacuum at idle. 15 says there is a leak.



the throttle body port on top is ported vacuum. you will not get an idle reading there.

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[Cloud9...68]

Your symptoms are different from the ones I had soon after I bought the car (it stumbled when warm, but drive fine when cold), but just the same, it's probably worth checking some obvious electrical components, like the distributor car, rotor, and plug wires. I wouldn't recommend just replacing things willy-nilly, but I would open up the cap and take a good look at its contacts, and the rotor as well. If it's been a long time since you replaced them (or don't have any record as to when they were), you might want to go ahead and replace them if they look at all suspicious.



Checking the plug wires is easy. Just wait till it gets dark, get away from any street lamps (you may have to pull it into your garage), start it up, and watch the plug wires for signs of any sparks. If you see any, it's time to replace them. Are yours stock, or aftermarket? In general. aftermarket plug wires haven't fared very well on our cars.



I agree the problem sounds more like a vacuum leak, but these sorts of problems can be deceiving, so you might as well rule out other stuff as well.

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[tamathumper]

Funny you should say that, I just got in from the garage where I inspected the rotor and cap. Both had no pitting, really more just a "flat finish" on both of their surfaces, so fine shape there. I had plug wires, rotor and cap in the cart at Pelican but decided to inspect them first. I did order new plugs, and I'll do the after-dark test for the (stock Behr) plug wires tonight.



flash, can you give me a couple of spots and values to test for vacuum? Or is there a place I can go to read how to do that test, and find out what "ported" vacuum is?

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[MB968]

I agree with Flash, 15 in vacuum seems low. I'm used to seeing closer to 20, at least high teens (but all on other engines, not the 968, but I'd expect it to be similar).



As far as testing the vacuum lines and the items attached to them: All the lines get their vacuum from the intake. Seems like there are just three or maybe 4 places where vacuum lines come off the intake. So, I'd pull each line and use a tool to pull vacuum on each line, and do a leak down test. As I recall, the same tool that can be used to pull a vacuum on brake lines (for bleeding) can also be used to pull a vacuum on other lines. I think Autozone has these on their "borrow a tool" program. Or they aren't too expensive at most auto parts stores. Pulling a vacuum on each line might be a little more deterministic than using pressure, as you aren't looking for the pressure leak/hiss. If the line won't hold vacuum, you can keep going downstream until you find the hose, or item that isn't holding vacuum.

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[tamathumper]

That's kind of the problem,... "pull each line" isn't easy when you don't know where they begin and end. Is there a diagram?



I'd imagine the Mity-Vac is the tool of choice? If so, I'll order one up tonight or tomorrow early in the AM, and it might be here by the time I get back. Just got back Friday morning from Vegas, and already have to leave tomorrow for a rousing tour of China. <img src="/forum/images/smilies/968/glare.gif" class="smilie" alt="" />

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[flash]

regarding the ported vacuum, take a look at where that port goes. you'll see the hole in the open part of the throttle body, looking from the inside upward.



as for tap points, i put a tee in at the fuel pressure regulator to test for full vacuum. as MB says though, they all get it straight from the manifold.



there are other places that can cause vacuum leaks.



the dipstick tube has a seal and a spacer at the bottom. those can leak.

the air/oil separator can leak

your oil cap is another common place for a vacuum leak. the o-ring is known to crack.



i also agree with MB968 on vacuum readings. typically you would see close to 20 at idle. given our cam overlap though, it's usually only 17-18. it definitely should not be 15



as for testing, the pressure method works very well. but, that's why you have to have a gauge at the MAF. that's the only way to see what it is holding. the manifold and entire intake system is too large to be able to create a vacuum that can be controlled for testing with anything we can buy reasonably.

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[tamathumper]

Will test again tomorrow, if I can find the time before the limo gets here, and a replacement tee fitting. The cheap plastic one that came with the kit broke into three pieces when I tried to remove it.

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[flash]

bummer. that's why the ones i send in the SC kit are brass.

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[Lear35A]

[quote name='flash' timestamp='1368970963' post='142897']

bummer. that's why the ones i send in the SC kit are brass.

[/quote]

There are quite a few OEM plastic tees and connectors (maybe elbows, too. I forget.) in the overall vacuum system in our cars. Did you replace all of yours with brass? If so, not a bad idea. Source?

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[flash]

i only have one OEM tee left, and it's the female one.



i get them from my hose guy. pricey for what they are, but worth it in my opinion.



you can probably get them from grainger or mcmaster.

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[tamathumper]

Surprisingly hard to find online, searching for either 4mm or 5/32", there are only a few sources and they are expensive especially when shipping is figure in. Quite a few of them are 2 bucks with 13 bucks shipping. I ordered up a new flexible plastic one and I'll have to look again when I land if there's time.

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[tamathumper]

OK, I put new plugs in it. Got the ones recommended in the thread about supercharged cars and plugs. The old ones were "tri-tip" Bosch and were in the 7 range. A few drops of oil in the center two holes, but not much, and I suspect that's from pressurizing the system to check for vacuum leaks.



I tested for vacuum at the fuel pressure regulator and it was 16-17, sweeping up and down between the two every few seconds. Car was cold and at idle. Leaving the hose disconnected did not effect idle. With all hoses connected, the severe stumble was still there, so more testing is necessary.



Is there any way to test the <acronym title='mass air flow'>MAF</acronym>?

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[flash]

yikes! those can cause detonation in a hurry. they don't cool off. on forced induction that can be a real problem. good thing you got them out of there.

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[tamathumper]

Yeah, based on that other thread, I figured they needed to go!

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