Electronic Q-Jet and Air Pumps - Team Camaro Tech
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post #1 of 12 (permalink) Old Aug 13th, 02, 09:41 AM Thread Starter
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Matt Jones
 
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Ok, this isn't for my Camaro, but for my '86 Chev 1/2 ton.

Ok, it's got the electronic Q-Jet. The motor was originally a 305, but I swapped in a 350. It runs fine at idle and under power, but it's lean during cruise (surges). What I need to know is, can I swap metering rods like the mechanical Q-jets? Do they use the same ones?

Now onto the air pump. What are they for? What do they do? I hate mine, because it make a funny noise, and makes the small block sound like a toy motor. Has anybody removed theirs and experienced any effects on emissions? If I can remove the thing and still pass emissions, I'll do it.

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1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
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post #2 of 12 (permalink) Old Aug 13th, 02, 10:23 AM
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Don
 
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On the carb, you can adjust the metering rods. On top of the carb there will be a hole that may still have a plug in it.

Using a special double D tool, and a dwell meter, clip the meter into a green connector that should be laying loose near the carb, and the other clipped to ground.

With the meter on the 6 cylinder scale, adjust the dwell to about 40, and it should be varying a few degrees in each direction.

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post #3 of 12 (permalink) Old Aug 13th, 02, 10:46 AM Thread Starter
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Matt Jones
 
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Don-
Can you explain your last two paragraphs? I don't understand.
Thanks,
Matt

------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my NEW webpage at: http://www.geocities.com/compuboy007/
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post #4 of 12 (permalink) Old Aug 13th, 02, 12:13 PM
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Don
 
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Matt, that's tough to explain without a hands-on demo, I went to all the GM schools back in the 80's when those carbs first came out.

Most of the tool trucks like Snap-on, Mac, Matco etc sell a kit to service those carbs.
It includes the special tools needed and the instructions.

If you wanted to, you could e-mail me, and I could give you the phone # here at the shop, and I could explain it better.

Those carbs can be real touchy.



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post #5 of 12 (permalink) Old Aug 13th, 02, 03:08 PM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by Silver69Camaro:
Don-
Can you explain your last two paragraphs? I don't understand.
Thanks,
Matt

<HR></BLOCKQUOTE>

I think I know what he is saying. The Dwell meter is measuring duty cycle. If you're adjusting breaker points, you're setting the ratio of time the points are open to the time between openings. The electronic mixture control in the carberator is a pulse width modulated device much like breaker points except the ECU adjusts the 'dwell' or duty cycle as needed. The ECU is adjusting the pulse width to control the mixture. I presume for the dwell procedure to work, the engine would have to be warm and in closed loop. The double D tool sets the metering rod height for the main jets at no load. Sounds like the ECU will set the pulse width of the mixture control based on the O2 sensor feedback. By manually adjusting the metering rods, the computer will compensate for the mixture change by altering the pusle width. 40% sounds like the baseline setting, so I presume that the mixture adjustment alternates somewhere between 40% and 60%. Am I close?

-dnult
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post #6 of 12 (permalink) Old Aug 13th, 02, 03:15 PM
 
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Per Beavis!

Uh, like WOW!!

He, He!!! pdq67



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post #7 of 12 (permalink) Old Aug 13th, 02, 08:45 PM Thread Starter
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Ah, I can understand that. Is that description correct, Don?

I was told by a moderator at ChevyTalk.com that the only 'electronic' part of the carb was a solenoid to switch from a double capacity accel. pump when cold, to half capacity when hot. So, when Don gave me his description, I was quite confused.

Now, this makes me wonder. I can get a very nice, clean Q-Jet from a '74 Chevy PU with a 350, all rebuilt for $75. Should I take off my electronic unit for this mechanical Q-Jet? I do prefer the mechanical, but I would like to still pass emissions. I also have a normal 4-pin module I could put in the distrutor (which currently has a 7-pin), recurve it on my machine, and drop that in as well. That way I can do away with, all together, the ECU. But from a reliability standpoint, is this a wise way to go?

Thanks for all your help guys. Don, if you don't mind, I would like to have your shop number. Drop me an email if you'd like.

------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my NEW webpage at: http://www.geocities.com/compuboy007/
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post #8 of 12 (permalink) Old Aug 14th, 02, 01:36 PM
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I believe the electronic mixture control carbs weren't much different than a mechanical carb except that the basline mixture was a bit leaner than a mechanical carb. The electronic solenoid is pulse width modulated. It may switch between extreams as stated, but does so at tens of hertz. The advantage of these things is that they fine tune the mixture as you drive. Mechanical only carbs are rarely optimal throughout the extreams of use. The downside is that the ECU that controls them is a bit craggy by todays standards. I hated the fact that they would spew out a half dozen error codes - most of which had nothing to do with the real problem. As a result, you had to use your noggin to troubleshoot them.

-dnult
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post #9 of 12 (permalink) Old Aug 14th, 02, 07:02 PM Thread Starter
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Matt Jones
 
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This is all new info to me. Very interesting stuff.

Now, is there a way that I can richen the mixture of the carb? I don't think it's running so lean that it may damage the engine, but I'd prefer not to run it this lean for too long. All the plugs are white, by the way.

Can I just go one step richer on the metering rods, or is there something else to it?

Thanks for all the great help.

------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my NEW webpage at: http://www.geocities.com/compuboy007/
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post #10 of 12 (permalink) Old Aug 15th, 02, 10:54 AM
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Eric
 
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The air pump (a.k.a. smog pump) pumps fresh air into the exhaust so there is enough oxygen to "re-burn" the exhaust in the catalytic converter. You will probably not pass an emmissions test without it.
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post #11 of 12 (permalink) Old Aug 15th, 02, 04:57 PM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by Silver69Camaro:


Can I just go one step richer on the metering rods, or is there something else to it?

Thanks for all the great help.

<HR></BLOCKQUOTE>

The double D tool will make the adjustment to some degree, but I'm really not qualified to answer. I wouldn't be surprised if the main metering rods (or thier seats) aren't a few stages leaner than the equivalant non electronic version. Maybe someone has a manual that would give the specs on the metering valves - or you could do like me and crack it open (gently). One thing the cruddy ol chilton manuals are good for is carberator data. Getting a manual of some sort would be a good thing to do first off. The tables in the back might lend a clue.

BTW: When a closed loop mixture system is operating properly, the porcelin on the plugs will be near 'antique white' and no signs of over-heat.

What is the compression ratio of your motor?

-dnult

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post #12 of 12 (permalink) Old Aug 16th, 02, 03:41 AM
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Send a message via AIM to Spames
This may help you-

"JET can custom tailor one of our Performance Kits to match your Vehicle/Engine combination. . ."

I would call them and tell them what you did. It sounds like they can send you a kit that should work perfectly with your engine combo.

http://www.jetchip.com/fuel/rebldkt.cfm

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[This message has been edited by Spames (edited 08-16-2002).]
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