Qjet troubles

[Richcz28]

1) what should the screw for the mc solenoid be set to? Like how many turns out.

(not my carb, extra sitting around)

2) I have a spot where on full throttle where the car bogs. It's between 2500 and 3500 rpms. The o2 reads rich here .8 on the voltmeter and the dwell is at 38.

At idle the dwell varies 48 to 54. The o2 at idle is mostly at .5-.6 more often than it is down. The car seeks at idle on the gauge between 600-800 but I haven't put a real tach on it.

At regular driving around 2000 the dwell is in the 30s but can get up to 48. The o2 is a little lower on avg than idle.

3) the car idles higher with a vacuum leak (booster disconnected)

So it's definitely running too rich.

 

[Richcz28]

Forgot to add 1984 e4mc carb on a 305

 

[Richcz28]

I disconnected the vacuum break for the secondaries and it runs wayyyyy better. No hesitation.

 

[Richcz28]

Any thoughts? Removing the vacuum break is just a band aid for now I assume?

Thanks

 

[Babaganoosh]

Is that screw for the APT? Meaning the part throttle adjustment how far the rods go into the jets? I have never messed with a solenoid carb. http://www.cliffshighperformance.com/tech_qjet_history_4.html

If it is I believe factory sets it at 2 1/2 turns out but every engine is different. I punched the hole out through my air horn and just kept driving and adjusting it until I found where it was smooth all the way through the rpm band.

 

[dyeager535]

You might try over at thirdgen.org. There was also a guy named Steve Harrison (email started with k0xp) that was an Oldsmobile guy who was pretty proficient with those systems. Google him and CCC, see if you can't dig up his email address and see if it works still.

I had started down the road to understanding CCC, but for all the work, it made(makes) sense to convert to EFI instead.

 

[Richcz28]

yeah I used to be on thirdgen.org a little but I don't feel like listening to the get an edlebrock or go tpi crowd.


re: babaganoosh
I don't think it is an apt but maybe a further evolution of it, it holds in part of the mixture control solenoid that works the two needles on springs that pulse in and out.

thanks for the website, it was a good read

 

[dyeager535]

Is there any chance you are getting knock retard? As I recall under heavy throttle the MCS goes full rich, if that's the case would seem odd to have a sag at mid-throttle due to MCS. How about timing? Baro sensor output is good? CTS is reading right?

It sounds like you are pretty well versed on this stuff, so if this is patronizing, it's just because I don't know your experience. Not intentional.

During acceleration it should definitely show rich. At the same time, a narrowband is not a very good gauge of AFR, since it's inaccurate anywhere but 14.7:1.

Additionally, at idle unless that's a heated or wideband O2 sensor, I'd be leery of taking the O2 measurements at face value. My setup shows roughly .45V at idle, and is quite a rough idle. If I get it up around .6V+, it idles far better. That's IF the O2 sensor stays warm enough.

With as many inputs as those carbs have (mechanical and electrical) I hesitate to say it's not something like a vacuum leak. Obviously the hunting idle could be from that.

 

[Richcz28]

I haven't checked the baro sensor and I don't know what the cts is.

How would you go about checking the baro sensor?

I don't have a ton of experience with the q jets only what I have learned from working on my own.

I'm also going to check out the map sensor.

Thanks for the detailed reply.

 

[dyeager535]

CTS is coolant temp sensor. Baro sensor I *believe* functions the same as the MAP sensor, but for some reason they called the early stuff baro, no MAP. Never researched it enough to see what possible difference it was.

If it turns out to be the same as a MAP sensor, you'd probably need to know engine vacuum at X RPM (if you can get a good reading), and what the voltage output on the sensor should be when its reading that vacuum. You could PROBABLY do this via the ALDL, but again, this is why everyone says convert to TBI...it's pretty hard to find info on this stuff, it's pretty primitive, and most have moved either to a regular carb or injection at this point. Typically through the ALDL (winALDL is a free program) you could see things like MAP voltage, etc.

 

[lectric80]

yeah I used to be on thirdgen.org a little but I don't feel like listening to the get an edlebrock or go tpi crowd.


re: babaganoosh
I don't think it is an apt but maybe a further evolution of it, it holds in part of the mixture control solenoid that works the two needles on springs that pulse in and out.

thanks for the website, it was a good read

Sorry I am not much help with the CCC, but I know exactly where you are coming from on the thirdgen.org site. Here people actually try to help, there it is almost like everyone thinks everyone else is an idiot and should be paying someone to do anything. You should hear some of the nasty stuff I got told when they found out my 83 was losing all the emissions crap and I was running a (gasp) non-CCC Qjet. In my case the CCC was long gone along with the 305, although the dizzy and everything else was still connected to the computer. The fact that I refused to even consider any type of injection until I go to an LSX really got things boiling.

 

[Richcz28]

Wouldnt the Baro and map throw a code on the computer if they were malfunctioning. Once before the cts was broken and the code came on. I know my computer is functioning properly.

 

[Richcz28]

I loosened up the screw that tightens the spring which closes the av flaps until it had no tension. This seemed to get a little better throttle response.

I have begun to notice some bogging lower in the Rpms like 1500-2000 under hard acceleration in 1st and 2nd. If
I get the engine above this it pulls smoothly.