Leak-down test...Analysis?

[Paul Workman]

Originally Posted by tomtom72

I was told the good stuff is Techron by Chevron. Black bottle any autozone or Costco has a 4 pack for about $20.00.

Paul, not to be forward.....I notice with mine that around town driving is the worst on my car. I go out with my vette buddies & try to keep up and the car never runs better...for a few days untill my around town driving "loads" it up again...if I drive it like a wuss = car don't seem to like it. If I beat it with an ugly stick = car seems to laught at me & wants more & she runs sweet. Oh, I'm using the std GM replacement plug for the FR2LS's that were OEM in my 90.


Tom

Yeah...I'm beginning to see that same performance pattern among some other Z drivers posting here and at that "other place". Mine too. After idling (especially from sub-freezing to just operating temp), mine went from running great to stumbling, balking, missing - primarily when giving it some gas. After it got warmed up good and ran the snot out of it a few times, all was well...Until next time.

Well, I bought some new plugs yesterday, and I'll get them in today and see what difference that makes - assuming the ones in there are original. My usual parts supplier didn't have the NGKs Jeff recommended, but he told me the Platinum/Irridium plugs are all made by Champion, as they're the only ones that have the tooling to make those plugs. According to his sources, Champion makes the plugs for NGK, AC/Delco, Autolite, and others...Interesting.

Jeff, if you're reading this too, I couldn't find the NGKs locally, so I cross-referenced them to AC/Delco #41-800 (listed for the 90 ZR-1). We'll see how they work later today, perhaps.

P.

[Aurora40]

What??? I'm pretty certain that NGK makes their own spark plugs.

[A26B]

Paul,
What you describe sounds more like it's just loading up from the idling. I'm sure that when you change plugs, you'll be looking at the old ones. Assuming the engine has been through a number of idling cycles, the plugs may be black. If it's loading up, the problem will return eventually after repeating the idling cycles.

Also, the LT5 is prone to oil collection in the plenum as a result of the crankcase ventilation system required on the engine. As such, oil may collect and add to the miss/load plug fouling problem until you "blow it out."

Another possibility is oil collection in the MAP sensor hose from the plenum to the underside of the MAP sensor. Will mess up the sensor signal. Just remove it and clean it out with air.

I like your style, go for the simple & no cost stuff first.

Keep us posted.

[Paul Workman]

Originally Posted by Aurora40

What??? I'm pretty certain that NGK makes their own spark plugs.

To clarify, specifically the info indicated Champion had a lock on the Platinum/Irridium plug technolgy(??). It was the plugs with that particular electrode combination which was reported to be made by Champion for NGK, etc. T'was a auto parts dealer that told me about the Champion making the plugs. Is it true? I dunno. I never heard that before either!

P.

Originally Posted by Paul Workman

Jeff, if you're reading this too, I couldn't find the NGKs locally, so I cross-referenced them to AC/Delco #41-800 (listed for the 90 ZR-1). We'll see how they work later today, perhaps.

P.

41-800 or the 41-808?

The 800 is not listed for a ZR-1, the 808 is.

[Paul Workman]

Originally Posted by Jeffvette

41-800 or the 41-808?

The 800 is not listed for a ZR-1, the 808 is.

I went back to the AC/Delco site and double checked. The 41-800 was listed for the 1990 CHEVROLET CORVETTE ZR-1 V8 5.7L 350cid GAS FI N Engine VIN = J

http://198.208.187.182/internet/Vehi...e=25&part=7212

In any case, the plugs I pulled were the standard AC/Delco 41-602s They looked new, and were not the least bit carboned up. Insulators were just off-white. Hmmmmm...... So, for grins, I ran over all the "zebra" clamps on all the vacume hoses. a couple were a bit loose.

Then I re-torqued the intake plenum. There I found about 1/2 of the screws were OK, and the other half took between 1/8 to 1/2 turn before they "clicked" at 20 ft# (FSM recommendation). I cranked her up and it ran smooth - not bad considering the ambient temp was 20º and the engine was cold soaked to be sure.

I then opened the valve on a bottle of propane and directed the gas around the edges of the plenum and the various vacume hose fittings/ends. There was not a whisper of affect and it continued to idle "sweetly" for several minutes before I cut it of (not yet at operating temp - maybe close to 100º at best.).

No chance for a roady today. The temp crept up past freezing and the sun is out. So, the road is a slimy mess. Further road tests will have to wait, but I do very much appreciate the support you and others have offered here. I'll do another "roady" as soon as possible.

Well, armed with the FSM and a VOM, I'll go and see what's up w/ my cooling fan(s?) coming on with the ignition, while I wait for a road test opportunity.

P.

[Paul Workman]

Originally Posted by tccrab

Paul:

The easiest way to check for leaks is to take a portable propane bottle (the kind the plumber uses), crack the valve just until you hear it hissing and then "spray" around all the vacuum hoses while the engine is idling. If there is a leak, the vacuum will suck the propane into the engine and the engine will momentarily idle higher. Viola! Leak found.

Good luck!

After changing plugs (oh...that #8 plug was "interesting"), I tightened all the "zerbra" hose clamps on all the various lines coming/going to the plenum. a couple were faily loose too.

Then I re-torqued the intake plenum screws (posted farther down the thread), finding a couple that required 1/2 turn to come to spec.

After that, I fired her up and did the test you discribed. No telling what might have happened had I done the test before tightening stuff, but in any case, the idle was smooth and there was no reaction to the propane anywhere around the plenum gasket or any of the hose connections.

For what it's worth, it seemed to idle as smoothly as it ever does...By that I mean a nickle would not stand on edge as there seems to be at least one cylinder that is not in tune with the others. It isn't missing. But, it gives the idle a slight throbbing noticed when placing my hand on the plenum when it is idling.

Freezin my bunz off, so I called it good for today. Oh, I did find out why the primary fan always runs...The control wire running to the ECM has been intecepted and intentionally run to ground. So, now the question is "why"? .

Thanks for the propane tip. I put that one in my "special tips file"!

P.

[tomtom72]

I'm wondering that would be the place to tap in for a manual fan switch, if one wanted to install such a switch?????

I'd say you dunn a good day's work, Paul!

Me, well I f'ed off with my vette buds....man them blown C6's sure are a hand full.....I think I run outta nerve too quickly! ....but at least my carbon is in the atmosphere now.

I would venture a guess that all those "small" items you found were affecting the car adversely....I did the same on mine awhile ago & it added up to something when all was said & dunn.


Tom

Ya know that's interesting about the plug technology....the plain jane GM ones seem to work for my car. Maybe some day I'll play around with some different ones. Thanks for the info on the plugs!

[Paul Workman]

Originally Posted by tomtom72

I'm wondering that would be the place to tap in for a manual fan switch, if one wanted to install such a switch?????

I don't see why not. Intercept the blue-black wire on the (left hand) fan relay plug wire and run it thru a plain ol SPST switch to ground. Throw the switch and the fan comes on instantly. (If you need a photo of where those relays are, lemmeno and I'll snap a pic for ya.)

P.