Running Rich or Lean? How to really tell?

[sblake01]

I used a Gunson Gastester when I had my Datsuns. I used it mostly to check CO which is more important than AFR when preparing for California's biennial smog checks. (I always brag about that fact that niether them ever failed a smog check during my ownership). I also did some AFR testing but I can't recall the numbers. What I like about it is that is can be used on any car since it's basically just an 'exhaust sniffer'.

Edited January 22, 2011 by sblake01

[madkaw]

The ideal mixture is 14.7, but can be on either side of that based on driving conditions. Some good info everywhere on this subject, but guys like to see maybe low 13's under W.O.T and atleast 14.7 under cruise for optimum fuel effiencency. Haven't played with mine yet(still in the garage), so I can't share any personal experiences

[argniest]

Oh yeah, one other thing, what kind of vacuum would I see if I connected a vacuum pressure guage to the car? And where would I connect it to get good readings?

I know there is a hose going from the port on the fuel pressure regulator to the intake manifold. Is that a place to stick it? And is it best to hook it up inline, like with a T connector...so the vacuum is just passing through it, while still not pulling off any hoses on the engine as to effect its normal operating performance, while you are checking vacuum readings?

When a person is trying to measure vacuum on a 1978 z car, are there multiple places to take readings?

And lastly, what is the vacuum it should be pulling? I thought I saw in the FSM its supposed to be -18.5inHg

thanks

Edited January 30, 2011 by argniest

[FastWoman]

You can hook up the vacuum gauge almost anywhere you want. I think Eric likes to tap the line to the FPR with a T-connector. I prefer pulling off the HVAC vacuum control line near the brake booster vacuum line and measuring from there. Normal vacuum should probably be at least 17, and 19 if you can get it. I'm pulling 18.5 at idle. Higher is always better.

[argniest]

Well, I put the vacuum gauge in between the FPR with a T, and the intake manifold. It was getting like 5 to 8, and bouncing around. That doesnt sound good. The only time it got up to around 18 was when I had it revved up to about 2500 rpm's.

So then I connected the vacuum guage directly to the hose leading into the exhaust manifold where the FPR normally goes to. And then I connected a vacuum hand pump to the FPR. And put it at 18 in of vacuum. So the FPR had the pressure I think it needed? about 18 in of vacuum.

When I did that, the vacuum guage was reading around 10 in of vacuum, but didnt stay steady, it kind of fluctuate between 9 and 10 ish.

In general I dont know how solid the vacuum is supposed to be. Since this is my virgin time ever looking at this kind of a guage. I know....Im a total noob. Is it supposed to be like rock solid at 18 all the time with very little flutter?

The car sounded different when I ran it this way. I dont know how to explain it exactly, but when I stepped back by the muffler it sounded different. And the engine seemed to be running different too...like a different overall sound to it.

And during this test I watch my fuel pressure guage. It was around 38 psi, during the first test, where the vacuum gauge was on a T, in between the exhaust and the FPR.

But when I applied 18 in of vacuum to the FPR with the hand pump, and it held that pressure during this whole test....the fuel pressure dropped to 32 psi. So that was what I found out. I dont know what any of this means. But figured I would throw it out there. I took videos of the engine running, and the guages showing these numbers during my 2 tests. So I will just keep documeting as I go along.

And also, one last thing the fuel pressure held up at about 25 psi over night in about 24 hours period. I left the guage on there, to see what happened.

[cozye]

Your FPR is good. That's what that tells you.

You've got a huge vacuum leak, or a valve issue. I'm surprised the car even runs with 5" of vacuum. The vacuum ideally should be around 18 at idle. anything under 16 would be unacceptable. You need vacuum to suck fuel and air into the cylinders.

http://atlanticz.ca/zclub/techtips/vacuum/

[FastWoman]

Eric, it might not be a vacuum leak. You can get a low vacuum with the engine running very inefficiently, where the throttle/bypass is opened up a lot to keep the RPMs up to normal idle. I suppose the throttle/bypass might be the vacuum leak, so to speak.

Argneist, you're using too many tools! Your FPR doesn't need 18" vacuum to work properly. Rather, it needs whatever vacuum is inside your intake manifold. Its job is to keep a constant pressure between the fuel rail and the inside of the intake manifold. That way the ECU can deliver a specified amount of fuel based on how long it opens the injectors. Anyway, by drawing 18in vacuum at your FPR when your manifold vacuum was really 5 in, you were leaning out your mixture (by causing your fuel pressure to drop).

But since you have that hand pump thingie and the vacuum gauge going at the same time, how about an experiment? Start without any vacuum on your FPR, and watch your vacuum gauge (on the intake manifold). Slowly apply vacuum to your FPR, and change your vacuum level around to find the point at which your engine idles its fastest/smoothest, with the highest manifold vacuum. That point would be your best mixture (at least at idle). Now compare the vacuum in your manifold with the vacuum to your FPR. That difference would be the amount you would ideally change your fuel pressure set point to achieve the ideal mixture. For instance, if you've got a manifold vacuum of 10 in and a FPR vacuum of 15 in, then you would benefit from an FPR that regulates pressure 5 in lower. Now divide roughly by 2 to find the difference in psi, which would be about 2.5 psi. So your FPR would be regulating about 2.5 psi too high.

But then again, at vacuum levels that low, other stuff is clearly wrong. I'd guess it's a lot more than your FPR. You might hang on to your FPR for a while, even if it's regulating a bit high. That might be OK if other parts of your system are running you lean.

[argniest]

Leak down test results! One of my jobs this winter, has been to do the leak down tests. It was not easy for me to understand all the things that needed to be done, in order to accomplish the leak down testing. However, once I understood all the little tricks to do it correctly, I have acomplished it.

Well I tried the harbor freight leak down tester, and it was definately not working correctly so I took it back. It could never get above 15 psi and I really think it was miscalibrated, and a piece of junk. I saw youtube videos also, of other people using it, and theirs never got above 15 psi either. That is not a good test. Especially as compared to the new one I got tonight via UPS.

After a lot of reading and finally getting a good leak down tester from online, I was able to accomplish the leak down tests. I talked with a mechanic friend of mine and explained everything I did, and he concurred that I did in fact do all the tests correctly. Basically what he said after two hours of talking about the test results, and everything else I have been testing this winter, he thinks I need a valve job. Cylinders 1,3,5 all showed an immediate 100% drop in pressure. So the leak down percentage guage went from 0% leakaage to 100% as soon I can connected the leak down tester to the cylinder 1,3,5. Cylinders 2,4,6 all had either about a 15% leakage only. Which is well within the range. ALso I heard and felt air coming out of the exhaust pipe on 1,3,5. And we listened with a air sensing mechanics stethescope to other areas on the car. It seems like the only real noticable leaking was from tailpipe on cylinders 1,3,5.

Soooooooooo, it is seeming like I am going to need a valve job. My mechanic friend was going to talk to me some more tomorrow night, and said maybe if I pulled the rocker cover I might be able to inspect a few other things. But we ran out of time and I dont know exactly what else he was going to have me check on the valves.

I am going to redo the tests again. Just to be 100% sure on the numbers. But I am sure I had the pistons at TDC for each of the tests. I validated they were at TDC by looking into the spark plug hole with a very bright LED light. And I could see that cylinders 3 and 4, 1 and 6, and 2 and 5 were at TDC at the same time. So I manuevered the pistons to TDC by turning the crankshaft pulley nut each time. Setting up the leak down tester first, locking the regulator knob, and then connecting the leak down tester to each cylinder at TDC.

Also, for the heck of it, I positioned cylinder 3 at what I figured was BDC, and I re-ran the tests. Well then the leak tester only showed like a 15% loss of pressure. I dont really know the technical reasons as to why at BDC it would be pressurized, but not at TDC. Maybe someone can explain that to me.

I also learned tonight that because of having these 3 bad cylinders (or what I mean is bad valves for those 3 cylinders) that could be the cause of all (or at least most of) my problems. I have low power from the engine, stinky exhaust, low vacuum pressure, bad gas mileage. I think these bad valves will overshadow any other possible problems with the engine and car runnability. And I am almost convinced now that is what needs to be dealt with next. I will be discussing this with a z mechanic tomorrow and also my cousin who restores cars. And I think they will probably agree the valves are hosed on cylinder 1,3,5. And since those 3(or maybe 6 of them) are bad, all 12 of them should just be replaced. Since I believe the front part of the engine has to be taken apart to do the job.

Also, I have low vacuum at idle (5 to 8 IN), and the compression tests showed that I have OK compression. 155, 150, 152, 150, 145, and 140-ish. I did the math, and they are just inside the acceptable range from each other. So that data tells me the piston rings are probably OK for a while anyway.

My fuel pressure is mostly OK...would take too long to explain in this post. Its already long enough now :-)

If it turns out that I really do need a valve job, can anyone suggest where I can get all the parts I would need to have this done? I wont be doing this job myself, because my cousin restores cars for a living. So he will be doing it for me. But I was hoping to find out where is the place to get good quality parts for this valve job.

THANKS

Edited February 18, 2011 by argniest

[FastWoman]

Argneist, are you SUUUURE you were at the "correct" TDC on each cylinder?

You see, the engine rotates twice per cycle. The cycle starts at what might look like TDC, when the exhaust valve closes and the intake valve opens. Then the piston moves down to draw in fuel/air. Then both valves are closed, and the compression stroke begins. Then the piston moves up as the engine rotates to the "REAL" TDC (the one that really counts). That's approx. where the spark would fire. The next stroke is the power stroke, where the piston moves down and applies force to the crankshaft. Then there's the exhaust stroke, where the exhaust valve opens and the piston moves up to expel the exhaust gasses. That takes us back to where we began.

If you want to be sure you're on the correct part of the cycle, you can confirm by removing the distributor cap and observing that the rotor is pointing to the wire position for the cylinder you're testing.

I suspect your engine is fine. I suspect you were just testing 3 of your cylinders at the wrong points in their cycle.

Edited February 18, 2011 by FastWoman

[argniest]

WOW what a difference a day can make! Today was a great learning experience about my engine :-) I just got back out there a little while ago, to retest those 1,3,5 cylinders. I knew I must have been doing something wrong. And now I know what it was!!!!!

It just didnt sink in about the piston going to TDC two times. But now that fact is crystal clear! On the exhaust stroke, of course the piston is at TDC AND!!! and exhaust valve is open. DOIH!!!!! And that is when i had accidently run my tests last night. Now I know better

Man that scared the life out of me. I just saw lots of $$$ leaving me forever, to get a valve job.

But now that I kept turning the engine back to the TDC of the compression stroke, geee guess what??? When I ran the tests tonight on 1,3,5 again, the 1,3,5 cylinders were also at about 18%. So that tells me my engine may not be perfect, but it seems acceptible for an engine with 182,000 miles on it.

I thought I read that even new cars could have a 15% loss, and that is just normal due to the layout of engines. If that is true, I am only 3% away from a new engine.

I feel soooooooooooooooo much better now. And I can get back to removing my fuel tank since I can see in through the fuel inspection plate with sending unit out of the way a little. And there is rusty crap in there, and all that rusty crap in the fuel filter, which btw, attached itself to a magnet when I moved it over the pile of crud that came out of the fuel filter. So that has to be rust. And the same rusty crap I see laying on the bottom of the tank.

At least I can see portions of the tank too, its not all rust. It just seems like its in some places and not in others. But as you know, cannot see very much through that little hole. BUt I would say maybe 50% of what I could see had pockets of that crap laying on the bottom.

So this whole experience has been wonderful for me to finally understand the 4 strokes the engine is making in one cycle. And now I can whip out a leak tester and do the tests so easily and quickly.

And now I believe I dont need a valve job!!!!!

Edited February 19, 2011 by argniest

[FastWoman]

Cool!

Please remit 10% of the money you saved to my email address via PayPal.

Nah... Just happy it worked out for you.

[argniest]

Cool!

Please remit 10% of the money you saved to my email address via PayPal.

Nah... Just happy it worked out for you.

you never know...maybe I will.