Understanding the Computer-controlled Quadrajet part 2

[@jamesruscio6536]

Tyler, great stuff, man. Appreciate your knowledge and patient explanations. That big mouth know it all, was the guy God had in mind when he wrote Proverbs 18:2, "A fool finds no pleasure in understanding but delights in airing his own opinions."

[@EarlGuyton425]

Hey Tyler, I am Earl, a long time mechanic. I watched your one video that was one hour and eight minutes in detail on those two rochestor carbs and learned soe good things. Than you for this education I now have. I have also watched these two videos on these computer rochestors quads and learned. I just did a partial rebuild on my computer quadrajet on a 307 olds engine in my 1989 cadillac. The only reason I took it of the engine and too it apart is because the accelerator pump was no good any longer. So i cleaned it up part by part and as I informed you in a previous video I cut out the upper gasket part that goes under the power piston, becuae that gasket portion isnt necessary . and can inhibit the up and down ovement of those power pistons. After I reinstalled this carb back on this car. The hot air choke and choke pull off works perfect and this car now idles super smooth, plus has no hestation when its reved up and no rich fuel or black smoke fro y exhaust at all But when I plug in that 3 prong TPS it pulls my idle down, so I left it unplugged. if something works perfect and no black smoke from unburned fuel and no hesitation at a on acceleration, then in my case what harm can happen by my leaving that TPS unplugged. And even though the engine light work with key on, it turns off when engine is running, so it will pass inspection this way. But in my case, based on a physics REALITY of some that runs perfect, yet doesnt run rich,this has to simply be okay.

[@johns2248]

Great informative series from back in the day. I had one on a 87 camaro 305. Nothing but problems from day 1. Total junk! I always wondered how it worked on the computer side!

[@MrZayne8]

I really enjoy your Quadrajet videos. I refer to them often.

[@TylersNeighborhoodGarage]

+MrZayne Thank you.

[@prun8893]

Thank you for making me understand why I have an Edelbrock.

[@76calidude]

WOW, I wish I would've seen this BEFORE I tackled replacing my MCS...lol. I own a 84 Chevy C-10 with a 350. Pretty much the same carb. Here in California, they have strict emmision standards, and I have to get my truck to pass "smog", every other year, or no registration. Of course this year it didn't pass (running too rich), and kind of figured it had to with the MCS because it stopped "ticking" a while ago. The Check Engine light was on too, so I just unplugged the light..lol. So, today me and my dad did exactly what you showed in this video, we just put everything back in reverse order. However, I did learn what exactly those two adjustments were from your video, the ones that were the MCS lean and rich mixture set screws...NICE!!! Hopefully it'll pass smog this time... excellent video!! Knowledge about these is becoming a drying art!, Rock on dude!!!

[@bricebabcock7156]

Can you remove or replace the electronic parts with manual parts? Can you tune the ecm with a computer? Can you tune it enough to put a mild cam in a 305?

[@anthonyanderson3408]

Hey Tyler, Love the videos. I have an 83 Cutlass with the 307. Recently the car started to stall while driving. I pulled the mixture control sensor plug (disconnected it) and the motor ran great, when I hook it back up, the car starts to stall, even at idle. When I tested the computer (with a paper clip to get the trouble codes) the solenoid started to click really fast.

[@wickerman9569]

Is there a way to check that mixture control solenoid? Thanks for the videos.

[@NOVATrek1701]

Thanks for doing these videos on the Qjet - they are a big help. I have a CC Qjet for a GM 305 that I'm rebuilding. Can you tell me what the little hook w/pin is on the underside of the air horn right near the TPS and how it goes on when you put the air horn back on? It just seems to hang there but I'm not sure if it's supposed to press onto the top of the TPS when reassembling the air horn.

[@mikegamer6104]

Like delete to mixture control function, can I install a shim inside to hold the mixture needles all the way down and run it. You said if you leave it unplug it goes to full rich. So if needles are held down permanently it might run ok?

[@macthemechanic]

I have an 88 Caprice. The caps for the idle adjustment screws have been removed already. It was running to rich on an idle test, and 2500 rpm test. Would I adjust the mixture screws on the front of the carb, or the stops for the primary metering rods? Should I hear the mixture control solenoid operating when the car is running? It seems to idle and drive just fine

[@TylersNeighborhoodGarage]

I think you are right. At this point I think the only 750 cfm version they had used a side fuel inlet which Olds did not use. So, cheaper to limit the airflow than to re-engineer another carb.

[@franmurphy9403]

On the electronic quadrajet, I am having trouble getting the throttle position sensor to stay down while putting the air horn back on. The real problem is the green pin that contacts the throttle position sensor pin and the accelerator pump arm is not lining up. When the accelerator pump is depressed, the green pin is not moving the plunger pin in the TPS. it is out of alignment with the TPS plunger pin. Any suggestions on assembling the air horn to get this correct.

[@AdamAllDayAndTomorrow]

Your videos have been great help. I have an e4me quadrajet. I took out the mixture control solenoid screw not thinking and then when I went to put it back in I forgot to count. I don't have a gauge to measure the gap or whatever. If I screw it til it bottoms out can I just back it out a few turns and be okay? Thank you

[@TylersNeighborhoodGarage]

+Adam Landon yes. Somewhere online there is data regarding how to rough that adjustment in at first. Past that you can simply drive around and see if it seems too rich or lean at part throttle cruise. There is a plug in the airhorn over the mcs adjustment screw that you can knock and then tap the hole for a removable plug so that you can fine tune it without pulling the airhorn

[@AdamAllDayAndTomorrow]

+WhoSaidTyler I have found a few adjustments and made my own gap tool with the measurements. I believe someone has already removed that plug on top so I will fine tune it, thanks again.

[@MemE-cd6jw]

Sir I have watched all the videos that you have posted about the Quadrajets. I am a Novice Mechanic. I am working on a 86 Chevy Monte Carlo. On the Quadrajet that I have I am referring to the Vacuum breaker. Even after the engine reachs operating temp. The Vacuum breaker is not releasing Vacuum to allow the Secondaries to open at all. Do you have some helpful advice for me so I may fix this problem?

[@mikegamer6104]

Can I swap those mixture needles with old style something so it runs like an old carb?

[@TylersNeighborhoodGarage]

Yes

[@Capricious9C1]

Ok I have a question, I have a 1989 Chevy Caprice wagon it came from the factory with a Olds 307 in it and the electronic feedback quadrojet on it. I had the carburetor rebuilt at about 160,000 miles I don't think either sensor was replaced. The car now has 262,775 miles on it should I have the sensors replaced due to age or leave them be? Real cold weather I got to pump the pedal about three times to get her started in warmer weather about two times. Car seem to run well no stalling or hesitating. I was just curious on those two things.

[@TylersNeighborhoodGarage]

If it runs well I wonder worry about it. Those sensors either work, or they don't. Occasionally the TPS can get a bad spot in it so the voltage signal back to the ECM drops to zero momentarily, but that's rare.

[@TylersNeighborhoodGarage]

WhoSaidTyler "wouldn't" worry about it*

[@Sterlingchiropractortherapy]

1986 Trans AM 305 computer quadrajet. Hi T, I am having some bogging from a stopped position when i accelerate. I am going to check: 1. Base and High Idle Adjustment. 2. Consider Tightening up the secondary air. 3. Mixture Settings. Am I missing anything? Thanks, J

[@TylersNeighborhoodGarage]

+NOVA Chiropractic & Rehab Center of Sterling Sounds good, only thing I can add is make sure the accelerator pump is working. If the carb hasn't been rebuilt in a long time the ethanol gas can eat the old piston cup.

[@dustyelliott9108]

Just came across your video after doing endless research to try and learn what these computer controlled Quadrajets are all about. I found out today after working on my 1985 k5 blazer, sbc 350 that there is such a thing as these carburetors. I have a question for you in regards to the throttle position sensor and the mixture control solenoid. After replacing my alternator and trying to clean up a previous owner's hack job on the wiring to the carburetor, I found that one of the wires to the mixture control solenoid was broken. I finished the alternator replacement and fixed the wiring but now I have a check engine light that comes on intermittently with accel/decel changes. What is funny to me is that the check engine light was fine with the wire to the mixture control solenoid broken. Would there be any sort of connection between the new alternator (holding higher voltage), disconnected wire on the mixture control solenoid, and the throttle position sensor (because the check engine light comes on with throttle changes)? Any advise is much appreciated.

[@TylersNeighborhoodGarage]

+Dusty Elliott broken wire may have disabled check engine light. Gm wiring design then was arcane. You need to jump the aldl connector and pull the code causing the check engine light. Instructions can be found online

[@dustyelliott9108]

In the time past since I wrote u my message I looked up some more info and ended up running the code. It threw a code of 23 which is the M/C solenoid. Now I'm wondering if I should just go ahead and replace the solenoid or focus on the wiring to the solenoid.

[@ivanpowers6436]

Great video, I have a 403 that has a carb from a 1981 Olds 98 with and Olds 307. your other videos were very helpful for setting the high and low idle. what would you guess the CFM of that carb would be? It is not computer controlled.

[@justinw523]

Tyler's Neighborhood Garage I just rebuilt a Q-Jet on a original 1986 Monte Carlo SS and its making a rapid clicking noise when I turn the key on then after min it'll stop, the car idles great seems to run ok but I didn't count the turns on the Mixture control sensor...any help would be grateful

[@TylersNeighborhoodGarage]

That noise is just the mixture control solenoid cycling..perfectly normal.

[@justinw523]

Okay thanks!

[@tallboyyyy]

I'm wondering why GM would use a carb that is way too big for the engine to use to it's full capabilities and have Rochester modify it down to where it would work on a small V8. The only thing I can think of is that it was cheaper for Rochester to modify a carb they already made than to design a new one that better fit the capabilities of the engine it was going to be installed on. This opinion comes from someone that only has a very basic understanding of carbs so take it with a grain of salt

[@daddyplease6884]

I would like to find the tool that adjusts the TPS on my 87 E4ME...they claim it's a 2.5 or 3mm nut driver. Where can I find one?

[@TylersNeighborhoodGarage]

There are a couple OTC 7667 tool sets on eBay now but they are about $70. Before you spend that kind of money, take a strong light and see exactly what type of hex you are dealing with in there. I bet something else can be made to work.

[@PaulCTownsend]

Good job

[@heartbeatstorm983]

Thats what im working on now,, so to me this is normal.. But on mine,, above the lean mixture solenoid screw,, there is no plug on the upper bowl,, its open.. Is that normal.?? Please wait at least one year for a answer,, after that none.

[@glennandreasson7813]

What would happen if you forgot The spring to the lean stop/rich stop adjustment? I just did a rebuild on my rochester and when it was all togheter I found The spring among my tools😬

[@TylersNeighborhoodGarage]

probably not going to work right. It needs to be there.

[@glennandreasson7813]

@@TylersNeighborhoodGarage thanks, I took it apart and fixed it👍

[@mqe73M]

I got a 1984 tans am what would cause rough idle on these carbs

[@TylersNeighborhoodGarage]

Same things that would cause them on a regular Qjet, since the idle circuit is purely mechanical. Broken vacuum lines top the list, then idle mixture out of adjustment. From the factory those screws are capped, you have to pull the carb and file away the caps. After than though, they can be adjusted just like any other. If nothing else the carb being dirty internally will do it as well.Good luck.

[@mqe73M]

+WhoSaidTyler why do they need adjustment if they are caped from the factory

[@TylersNeighborhoodGarage]

mqe73M Because over time the operating conditions of the engine change and the carb becomes dirtier. It's hard to explain, but on older carbs, adjusting the idle mixture is just considered part of routine maintenance.

[@TylersNeighborhoodGarage]

The easiest thing by far is to get yourself to a junkyard and grab one. They are not rare or hard to find by any means. You can decode GM Rochesters easily because the number is cast into the carb. But, Most Ford Autolite and that Carter BBD you have used a tag held on by an airhorn screw. So, if the tag is gone, no decoding. The number cast into the side of a BBD is meaningless. Sorry man.

[@markridings6687]

Informative but needs to get to the point and move onto the next thing. Too much talking not enough information.

[@luispina4012]

Junk carb.