A day of testing

[ll77]

I have a 76 280z that runs rough, lacks power, and is quite gas-inefficient. I checked my air temp sensor and water temp sensor w/ a multimeter, and they read acceptably. I hooked up a vacuum gauge with a T at the FPR vac line, and these were the results:

~10.5 in Hg @ 800 rpm (not jumpy, but twitchy)

(I don't have a tachometer yet, sorry)

drops to ~4.5 in as throttle is applied

raises back to ~10 in to WOT

up to ~20 in @ throttle release

Fuel pressure (gauge is not very accurate)

39 psi (idle)- 42/43 psi (throttle applied)

I tried messing with the AFM (PO put wrong one on the car)- gave it more fuel while also decreasing idle back to 800 rpm (my dad was screaming the tach reading to me over the exhaust hahaha) and my vacuum started drifting steadily between 15-17 inches, which would be more acceptable.

I don't have any big irregularities except for the fact that the vacuum is SO LOW, and I understand that is causing my very high fuel pressure.

I checked my valve timing, I cranked the crank pulley till the timing mark was at 0 deg BTDC, so TDC.

Weird side note: my intake/exhaust cam lobes were making 11:15, if the intake were the hour hand and exhaust was the minute hand (relative to timing chain). Also the dizzy was pointing underneath the upper radiator hose, looked as if it were already touching the #1 plug wire contact. That don't seem right.

So anyways, I looked to the marks on the cam sprocket, and the triangle was waaaay to the EDIT**right of the mark. So I'm too advanced, I wonder how that happened.

Then I decided to look at my PCV valve, so I popped off the hose under the BCDD going to the intake manifold, nothing there! Just a bunch of carbon. Whaatt? I need a PCV valve.

SOO, I've gathered I need to adjust my valve timing, and the right model AFM would help too, yeah? What do you guys gather from this? Thanks a bunch for any input!

Edited August 17, 2011 by ll77

[Zed Head]

43 psi is high fuel pressure. Almost 20% more pressure than the system was designed for. Either your regulator is bad or you have some blockage on the return line (or a bad gauge). The low vacuum is not causing your high pressure, you're well out of the normal range of fuel pressure. It should be 36 psi with the vacuum hose pulled off of the FPR.

Have you tried removing the oil filler to see how the engine's running is affected? That is a fairly good sign of how well the crankcase is sealed. If you already have a big vacuum leak, you won't see a big effect. My 76 280Z notices the extra air when I take the tiny AC accumulator canister hose off of the manifold.

What's the number of the AFM?

Edit - fuel pressure effects comes up every now and then so I looked around and found a calculator - http://www.rceng.com/technical.aspx

At 43 psi, you're pumping in about 9% more fuel than design. It's like having a 205 cc injector instead of a 188.

Edited August 17, 2011 by Zed Head

[ll77]

43 psi is high fuel pressure. Almost 20% more pressure than the system was designed for. Either your regulator is bad or you have some blockage on the return line (or a bad gauge). The low vacuum is not causing your high pressure, you're well out of the normal range of fuel pressure. It should be 36 psi with the vacuum hose pulled off of the FPR.

Hmm. I have not tried that yet, I'll try tomorrow. But it could very well be the gauge, it acts very strangely, I'll definitely put in a new gauge too.

Have you tried removing the oil filler to see how the engine's running is affected? That is a fairly good sign of how well the crankcase is sealed. If you already have a big vacuum leak, you won't see a big effect. My 76 280Z notices the extra air when I take the tiny AC accumulator canister hose off of the manifold.

Do you mean the oil cap on the cam cover? I'll try that too, and I also suspect a vacuum leak, perhaps at the manifold gasket. There is a hissing noise, but I've sprayed propane on all the vacuum hoses, fittings, and CSV.

What's the number of the AFM?

a31-625-000. I believe it's a later 77-78 model.

[ll77]

Yeah, the gauge really is terrible, it's probably not that high. I'll update tomorrow when I put on a new gauge.

But since my vacuum is so low, I really suspect the valve timing since it seems to be ridiculously advanced.

[FastWoman]

I have to go, so I don't have much time to post. I'll be back later.

IF your fuel pressure is high, it's going to contribute to rich running. Your problem is opposite. So if you fix the high fuel pressure (e.g. replacing regulator), it's going to make your engine run worse. That doesn't mean it shouldn't be fixed (if it's broken, that is).

Your first job is to search for vacuum leaks. All your vacuum tubing, if old, is suspect. I'd replace all old tubing/hoses with new. It's an easy job. Also check the big rubber boot between the AFM and throttle body for splits/cracks.

Some of us are finding that our ECUs have drifted over the decades, resulting in inadequate fuel delivery. There's a remedy for that, but before doing it, you have to get everything else straight with your engine.

BTW, since you've been into the ECU, take a look at the silicone rubber blobs on the clock-spring wheel. Do they appear to be factory blobs, and are they still intact? It's important to figure out whether anyone's tampered with the AFM's factory settings. If so, you may need to recalibrate.

Finally, you can download a factory service manual for free from xenons30.com. Go to section EF, and you will find lots of diagnostic procedures you can follow. There's a big connector on the ECU, just under the driver's side kick panel. I'd suggest doing all the electrical measurements there. It's a good way to check both your components AND your wiring and connectors, all at the same time.

[ll77]

Bad news, oreilly's didn't have in-line gauges, PCV valves, or chain tension retainers for me. I guess it's time to shop.

I think I'll take her to the shop to get the chain adjusted, dash removed (so I can check my hazard flashers), and injector screws loosened up (totally rounded).

I put in a new FPR a couple months ago b/c of the reading from the gauge. When I get a new gauge (today?) I'll get a good reading for you guys.

About the AFM, I have the wrong model for my year, so I adjusted (leaner) to try to compensate. My smog report says I'm waaaaay rich. Also it is a "fuel injection corp." rebuilt AFM. I've heard that rebuilt AFMs have an issue with their counterweights, creating extra resistance at the flap, making it lean at idle. Makes some sense right?

Oh yes, the boot is cracked. I tried to sealing it with rtv, don't know if it did any good. I hope to have an AFM w/ boots coming real soon.

I have a bunch of fuel and vacuum line sitting, I'll throw it on ASAP. Just been discouraged by the injector screws (wanted to change all the lines at once haha).

I also have the EFI bible and I've performed all the tests on there, everything's ok. But I haven't performed the Air and water temp sensors hot yet.

I'm off to put everything back together and go shopping now.

I'll keep you guys posted, Thanks!

Edited August 17, 2011 by ll77

[ll77]

Ok I bought a oil pressure gauge today b/c I read that those are ok for my application between the fuel filter and rail. I can't believe how hard it is to get one for fuel injection applications! I'll get the fitting tomorrow, but I might take it in to the shop tomorrow too, so I might not have the car for a while. I'll have updates ASAP!

Oh yeah, and I had a bit of a thought bubble today. I learned in my physiology class that when blood capillaries contract (get narrower), blood pressure increases because blood must travel through a smaller area. Could having smaller diameter fuel line also increase my fuel pressure? The fittings on my FPR seemed to be very tight for the hoses, perhaps the PO used the wrong size fuel line. Hmm... any thoughts?

Edited August 18, 2011 by ll77

[FastWoman]

You can get "T" fittings at any hardware store for your fuel pressure gauge hookup. You'll want a "T" fitting with 5/16" barbs.

Is there any reason you're wanting to change out injector hoses or injectors? If you don't need to do it, I wouldn't. When I suggested changing out vacuum lines, I only meant vacuum lines. Even if you want to change out fuel lines (not a bad idea, really), I'd leave the short hoses on the injector rail assembly as they are.

You'll definitely need the correct model of AFM to start with. You'll know much more about your engine after you get that corrected.

Fuel pressure and fuel line diameter -- You've got a lot of factors mixed up here, but a blockage in the return fuel line could cause an elevation in fuel pressure. However, a smaller diameter fuel line isn't going to amount to much. Fuel isn't gushing through those lines like water through a fire hose.

If you're tweaking your afm to open up the vane (to deliver more fuel), and if that makes the engine run better/stronger, with more vacuum, then you're ordinarily running too lean, not too rich. I don't care what the smog report says. The split in your boot could be part of the problem. You can still buy that part new from Nissan. Try Courtesy Nissan on the web.

You don't need to remove your dash to check your flashers. Your flashers are up under the driver's side dash. Just lie on your back on the floor, and look up. There's one for the turn signal and one for the hazards. If I recall correctly, the hazard flasher is up above the hood release somewhere. If not there, it's near the steering column above the pedals.

[ll77]

Great, thanks for the info! I get to work on her more before school starts next week then, great! Gauge and vac lines will definitely go in tomorrow!

[ll77]

Again, I come home for lunch empty handed. Local hardware stores couldn't help me with the fitting, nor kragen. I will continue my quest after I eat.

On another note, I took off the oil cap while it was running and I immediately noticed the difference, and it was a big one. So no giant vacuum leaks then.

[FastWoman]

Again, I come home for lunch empty handed. Local hardware stores couldn't help me with the fitting, nor kragen. I will continue my quest after I eat.

I'm surprised! Just go to the plumbing section. Look in the parts bins for small brass fittings.

On another note, I took off the oil cap while it was running and I immediately noticed the difference, and it was a big one. So no giant vacuum leaks then.

Well, I don't know how much this really tells you. I know for a fact that my engine is very tight, but I don't get the same huge difference when I pull the oil filler cap. I do get air throught he hole, and the engine runs a bit rougher, but it's nothing dramatic. I think that has to do with my PCV valve, which is new. I think it passes less vacuum than my prior PCV valve did, and with that valve, there was a more dramatic difference when removing the oil filler cap -- even though I had vacuum leaks going on at the time!

There's a quick way to test for vacuum leaks. When you get your new AFM and boots, first connect up just the boot that goes to the throttle. Then stuff something (I use a yogurt cup) inside the boot opening to block the air. Pull off the vacuum hose to the brake power booster, and attach a hose to the manifold that you can stand to put in your mouth. Then blow into the manifold like you're inflating a balloon. The pressure will build, until you can't blow anymore. Just hold the pressure there, and see how long it takes to dissipate. It should take probably 15 sec or more for most of the air to leak back out. Then pull off the little vacuum hose beside the brake booster hose, and repeat the test. You'll see/hear/feel lots of air coming out through that little nipple, and the air pressure should leak down MUCH, MUCH faster. If there is a dramatic difference between the two, your intake and engine are tight. If the difference isn't very dramatic, you have a leak somewhere.

If you do have a leak, I suspect you can find a smoker (hopefully not you!) to blow cigarette smoke into the manifold. It should come billowing out wherever you have a leak. I've never tried this (non-smoker living amongst non-smokers!), but I bet it works quite well.

[ll77]

So here's how my day went- I went to 3 different auto supply stores and 2 hardware stores, no one had anything for me. It's crazy, it seems like such a simple piece, but I can't find anything around here. I asked them for a barbed T that would fit my gauge, nothing. I looked to see if I could make a piece with a T and some adapters, nothing. Most Ts were too big to fit my gauge. I tried to find an adapter to hook it up to my current T, nothing. So I tried to get a gauge with a larger threaded fitting, all were the same except an air tank press. gauge, which would have threaded on to my current fitting perfectly! This is so frustrating, I can't believe I just spent a whole day trying to get a gauge on! I think I'll just shop online for a solution tonight. This sucks!

I have no PCV valve, so I must be passing lots of vacuum through the fitting when I pull the cap.

I have heard of the yogurt cup test, I just didn't know exactly what it was, just that it involved a yogurt cup haha. So I blow like pshhh, wheeze, pshh, wheeze, pshh wheeze, etc? Thanks for writing it up for me. And lucky for me, I have plenty of auto tech friends that smoke, so I'll get one of them to do it for me.

And I found my flasher units today! Thanks, I'll post when there's anything new!

Edited August 19, 2011 by ll77