Idea for EFI mod

[sblake01]

[FastWoman]

The motor is within specs -- 165-172 dry compression, 13 deg BTDC timing (10 deg works almost as well), valve timing still within #1 hole range, valve lash is right. Absolutely NO leaks anywhere. All sensors are to spec, including the AFM.

I pull a more or less normal vacuum now (18.5 in Hg). I'm sure if I had a fresh engine I'd pull higher. Combined mileage is 21 mpg. Acceleration is brisk. Plugs are clean, with a hint of mocha, but not chalky. Exhaust is clean. Motor sounds good. Idle is smooooth and easy. Runs like my '75 did back in '83 after I got it straightened out.

... but feel free to disagree. What do I know? :stupid:

Edited December 11, 2010 by FastWoman

[FastWoman]

Anyway, if you don't believe in my little mod, don't use it.

There, that was simple.

[Zed Head]

You know, it's possible that your motor runs perfectly by 1978 standards. We might all just be spoiled by today's numbingly smooth modern machines. Or fuel quality has changed and your motor really is running lean. They say that today's E10 and E15 is not "noticed" by today's engines but they all have O2 and knock sensors feeding smart computers to keep the ratios correct. The E85 guys all run a whole extra set of injectors or really big ones to make their engines work, so it's just a question of how much leaner is E10 or E15, and the effect on your idle. Maybe it's not capacitor drift but fuel composition drift. The topic has been well-worn re gas mileage but I haven't seen much on little things like idle quality, etc.

Nothing wrong with some new technology to get things back in sync.

[cozye]

mine was running so lean it was undriveable. backfired through intake, stumbled, lean surged, etc.. Lean mixture will cause low vacuum. The problem is it is difficult to tell if the lean condition is caused by low vaccum, or low vaccum caused by lean condition. I can guarantee you there are no intake leaks on this car. You guys can disagree all you want about ecu drift, but after months of trying to find non existant intake leaks, messing with cam timing, ruling out every single possible cause of low vacuum, all that I was left with was ecu drift. Same as Sarah. We both replaced intake manifold gaskets, all vacuum lines, etc.. I personally used over 6 cans of carb cleaner and a whole bottle of propane trying to find leaks. I did a boost leak test, and used a smoke machine. And when all is said and done, including 2 different threads on zcar.com that lasted over 50 pages, the old school guys chime in and say that it's a well known issue with z mechanics, and the fix is to put a resistor inline with the water temp sensor.

Once proper resistance was added to the water temp circuit, vacuum comes up to 18.5hg and the car runs perfect.

If anyone feels strongly enough to differ, I'll offer the challenge for you to try your theories on my car. It's easy to be an arm chair mechanic, but you go pulling your hair out for 6 weeks trying to get a car that's firing on all cylinders, using new injectors, with proper fuel pressure, no intake leaks, and consistent compression across the board with a good leak down test running right and you might feel differently.

Here is 6 weeks of my life unfolding

http://www.zcar.com/70-83_tech_discussion_forum/is_my_fuel_pressure_regulator_bad_893825.0.html

http://www.zcar.com/70-83_tech_discussion_forum/is_it_time_pull_head_894425.0.html

In the second thread you will notice TonyD mentioning (in between his caustic rants) towards the end that this is a well known issue and the resistor is a common "field fix",

More info on drift and the water temp sensor fix

The Z Doctor recommends fix and mentions aging ECU

http://www.zcar.com/70-83_tech_discussion_forum/backfire_871219.msg2491779.html#msg2491779

If someone can prove 100% that there is another reason for mine and Sarahs car to run lean other than the conclusion we came too, I'll give you $500

Edit.. this whole problem was so frustrating to deal with, that I don't feel like reliving it. If you have a suggestion, read all 50+ pages of those two threads on the other forum before asking me "have you tried this", because I'm quite sure I've already tried it or tested it.

Edited December 11, 2010 by cozye

[FastWoman]

Zed Head, I get what you mean, and I've briefly wondered that myself. However, engine vacuum is a pretty good and objective metric of engine operating efficiency. When an engine is running at 19 in Hg at idle, it's got a good mixture going, and it's hitting on all 6 pretty smoothly and cleanly. When it's pulling 14 in Hg, it's probably either too rich or too lean, or something else is going on that shouldn't, and it's not running so well. That hasn't changed over the decades. In fact I'm still using a vacuum gauge that is older than my car, and its scale has green zone painted on it that indicates a "normal" cutoff of 18 in Hg, so nothing has changed. My gauge is still accurate too, as it indicates vacuum in the "green" 18-21 in Hg zone for modern engines, such as the inline 6 3.0L VVT on the Z3 I recently fixed up. (NICE engine! )

I do think the E10 issue has some merit, especially since our E10 is really sometimes E20 or E30 by the time we're able to pump it into our tanks. (Everyone likes to harvest those tax incentives, even when it's illegal to do so, and they don't care what it does to our cars.) Of course as you point out, there's less energy per volume of E10/20/30 than there was in our wonderful E-ZERO, so old engines on modern gas run a bit leaner when delivering the same fuel volume per unit air volume.

That said, the differences aren't really all that great. I think they impact our open loop EFI more than a closed loop EFI or carb system, because the latter two systems have adjustment capabilities, and the open loop EFI doesn't (ordinarily). Even so, it's not all that big a difference.

By comparison, the mix problems Coz and I were experiencing were huge. He described his. Mine were similar, except that I could maintain an idle. My exhaust would blow and puff, and I had occasional backfires (which would never happen with a properly running street engine). These were things that didn't happen with my engines back in the day. My memory may have drifted as to how smooth our engines were, but it hasn't drifted as to issues of engine vacuum and backfiring.

To put the problem into perspective, another final adjustment I considered for the mixture problem was to run a higher fuel pressure by changing out the FPR. I thought I might be able to even out my mix by bumping the pressure a few psi. To test this idea, I pulled the vacuum hose to the FPR at idle and got some improvement in running. I then applied air pressure to the FPR as a "boost" and was able to drive the differential between fuel pressure and manifold vacuum as high as 50 psi, limited by my fuel pump. The engine ran much smoother but wanted a bit more fuel still. I think I was pulling a vacuum of 17 then. I'm guessing I might have achieved the right mix at 60 or 65 psi if I could go that far. Of course roughly double the pressure doesn't mean roughly double the fuel, as I don't know where Reynolds numbers start kicking in. However, I think I can safely say that double the fuel pressure is a LOT more fuel and that the abnormalities in my mix were quite substantial.

Anyway, as Coz points out, we're re-discovered what the old-timers already knew and reinvented the fix for the problem. Of course I AM an old-timer when it comes to electronics, having worked with every generation of electronics to present. (I still have my tube tester and a maybe 40 lb box of spare tubes!) I already knew that semiconductors break down over time, particularly the early ones if oil leaks out of the little can. For me, electronics wasn't about making a radio or TV work. It was about high precision instrumentation that had to be dead-on accurate. (I was formerly a scientist, before research funding went the way of the dodo.) So when a component drifted, I KNEW it. In fact I had a practice of socketing all of my linear semiconductors (both transistors and ICs) so that I could easily replace them when they went out of spec. ICs were of course very robust, but they would sometimes lose some of their output voltage range, pegging out farther and farther from the supply rail voltages. Transistors would mostly lose gain.

The degradation of electronic components over time is well known and widely discussed. Semiconductors break down from heat and the passage of time. Holes migrate and cluster. Junctions weaken, and metals migrate. Not even digital circuitry is immune. Ever notice how a computer runs hotter and hotter as it ages, until one day you get the blue screen of death?

Anyway, our ECUs take a lot of punishment, not the least of which is being operated with poor ventilation in a car that's just baked in the sun for 5 hours. It's perhaps a wonder they still operate at all.

Edited December 11, 2010 by FastWoman

[FastWoman]

BTW, another factor here is that people have different standards for old engines/cars than for new ones. They expect them to run worse with the passage of time. Even professional mechanics share this expectation, strangely. When there's an "annoying" engine light that won't go away, it never occurs to the mechanic that there might actually be a problem that has eluded diagnosis. It's just dismissed as "fussiness," and the light is reset. That happened with several of the PO's dealer service experiences with my Z3. The problem was a crack in the intake boot between the AFM and throttle body, a coolant sensor out of spec, and lots of varnish in the valve train. After I corrected that, it purred like a kitten.

Same with my 280Z. The local Z guy thought my engine was running well, but it didn't really run well until I fixed a substantial intake leak (replacing the manifold gasket), replaced a stuck (open) cold start injector, replaced all of the regular injectors, replaced a bad coolant temp sensor, replaced all of my electrical connectors (some of which weren't connecting), and calibrated my mix with the resistor in series with the coolant temp sensor. NOW my engine runs great.

Next engine -- my '92 Saturn SL-2, basically not much done to it since I bought it in '91, aside from plugs and wires. Everyone thinks it runs great (for an old car). However, it hesitates in the cold, and the exhaust doesn't smell right. Next spring I'll be replacing the injectors, testing the sensors, probably replacing the O2 sensor, definitely cleaning the little hot wire (!), and whatever it takes to put it right. There's potential for a flawlessly running engine in there, and I know something's not right.

I don't know why people think old engines have to run badly, but they do. Strange.

[Mikes Z car]

FastWoman,

Thanks for sharing the details on aging failure modes for ICs and transistors. I didn't know age would cause transistor gain to drop off and ICs would get further from the supply rails. That is a very nice insight I never ran across before.

Mike.

[ZCurves]

... calibrated my mix with the resistor in series with the coolant temp sensor. NOW my engine runs great.

Sarah, I know that you described this process somewhere but I can't find it. Please re-iterate (give me a link). I would be much obliged.

[FastWoman]

I think the discussion starts around post #57 of my "purs like a kitten" thread (page 3):

http://www.classiczcars.com/forums/showthread.php?t=40234&page=3

I don't have a well developed calibration method, though. I suppose I'd really need a dyno to do it right, but that's beyond my means or level of seriousness. I currently err very slightly on the rich side - "old school" conservatism. I'd shoot for a bit leaner if I had a cat.

[ZCurves]

I think the discussion starts around post #57 of my "purs like a kitten" thread (page 3):

http://www.classiczcars.com/forums/showthread.php?t=40234&page=3

I don't have a well developed calibration method, though. I suppose I'd really need a dyno to do it right, but that's beyond my means or level of seriousness. I currently err very slightly on the rich side - "old school" conservatism. I'd shoot for a bit leaner if I had a cat.

Thanks - you're a gem!