This problem started as soon as I got the car back from the smog shop last year. Runs perfect when cool but as soon as the car heats up, the problem begins. Example of what's happening... When stopped at a light or stop street when first taking off again, the car starts to go for about 1 second then totally cuts out for 2 or 3 seconds, sometimes more. Now this isn't WOT take offs, this is just enough pedal pressure to get the car moving. If I do try and do a WOT take off, the car bogs down extremely bad for a good 5 seconds or more(I've almost gotten t-boned due to it running this way) The problem only happens in the low RPMs, like 1000 and below. (car idles at 600)

The Q-jet was newly rebuilt along with the 305 before I took the car to the smog shop. It's been looked at by 2 different shops and they can't find anything wrong. One richened up the mixture so much that it was turning the new cat purple so I leaned it out a bit again. (3 1/2 turns out on both sides)

I'm almost to the point of buying a new Carb and hoping for the best, but the car didn't have this problem before rebuilding the engine and 2 days before taking it to the smog shop. Plus it runs good above 1000 rpm.

'82 Z28, stock auto tranny, Edelbrock Performer intake, 3in exhaust, K&N air filter, CompCam EX256H, and about to get the 305 S/R Torquer heads plus the Edelbrock's TES headers.

Any help would be most appreciated.

 

I'm thinking the power valve is stuck or sticking. The accelerator pump gives the initial shot of fuel, but it's only a squirt(which explains your initial accleration before the bog). The loss of vacuum at throttle tip in should allow the powervalve to give more fuel to the engine.

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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

 

From what limited reading I've done today on the Q-jet, one of the articles said there is no power valve but I did see power piston mentioned a lot. Same thing? Looking through the instructions that came with the rebuild kit, I didn't see anything that says either of those names. Grrr, hate not knowing too much about carbs.

 

Do you guys stop to think for one second before you start offering theories on what is wrong. Did you ever think maybe has a leaky injector? Or maybe his opti-spark is on its way out?
Of course those theories make no sense. But they are just as valid as the ones you offered. They could give the same symptoms, if they were parts on his car.
What am i getting at. You guys start offering ideas without any idea of WTF you are talking about. His car does not have a power valve, or a power piston. It's CCCS. In the future if you're gonna pull a theory out of your *** , don't bother to respond cuz you're just going to confuse somebody....(getting off my soapbox now)

As to your problem. Either your TPS is bad/maladjusted, or you have an ignition problem. Could be a general tune-up issue (worn parts/timing) or maybe something a little beat in the distributor (pick-up coil, etc.)
...ed

 

Actually, now that i think of it more, you might be working on 2 problems, or one big one. That it bogs really bad if you floor it doesn't seem much like a TPS, that surfaces more as a light throttle stumble. Of course, you could have 2 problems, a beat TPS and a too loose AV (or clogged/missing secondary "acc. pump" discharge tube.)
Or it could be one more global problem, like a sticky/bad VAC sensor. Or still something in the ignition.
It's really hard to diagnose something like this over a computer, but those are some ideas.
...ed

 

Think I may have just one big problem. (or at least I'm hoping lol) Let me give you a run down on what I've done so far in the past months that haven't cured the problem.

New distributor, new coil, new sparkplug wires, I think all of the vacuum sensors are new now trying to chase the problem, some new vacuum hoses, TPS was adjusted (will check again today), valve lash was set by a shop, carburetor was looked at by a guy who worked for GM on the Q-jet carbs and said it was ****, EGR valve works properly, timing set at 13*, checked carb base to see if warped which it is slightly but has a good seal showing on gasket, throttle blade shafts have new bushings.

The engine only has 2000 miles on it. Come to thing about it, it is just a stumble but far from a light one hehe. If I very slowly start pushing the pedal down like some 100 year old lady taking off it's not as bad. Soon as I start off like a normal person, it stumbles for a second or two. After long drives the problem is worse. Gonna try swapping carbs this week off another Camaro and see what happens if I can't get it going right in the next couple of days.

 

A couple of places to look:
Choke pull-off: If inop or leaking badly, will lean out the mixture, especially off-idle transition. Could be the reason for the WOT bog as well if it isn't delaying the opening of the AV.

Air cleaner: Do you have an open element, or is the K&N in your factory snorkel-type housing? If open, you're not getting the warmer air that is intended to help that off-idle transition. If snorkel, check your vacuum servo on the snorkel - if not working, same effect.

Your timing sounds pretty far advanced. I believe 6 degrees is the max setting the factory used for LG4's or 69's. What happens when you set it to 6? I don't think you have a knock sensor, so that wouldn't be a contributor, even with the advance you're running.

How much of the adjusting did you do when the carb was rebuilt? "Rebuilt" doesn't necessarily mean "properly adjusted".

Like Ed said, you may be dealing with more than one problem.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 2.73 open, cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, ported heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

The air cleaner is the factory setup just with the filter inside. The servo on the snorkel works properly. As far as the timing, everyone has said, if it's running without pinging don't worry hehe I'll change it to factory specs tomorrow and see what happens. Carb adjustments, they were done by the smog shop trying to track this problem down, I stood there and watch him do it. Also there is no WOT bog above the 1000 RPM mark, only below 1000 RPM.

 

Well, that eliminates one thing.

AV bog will often go away when the RPM's are up high enough. That makes the pull-off suspect. If it is working otherwise (opens the choke slightly when started), then try adjusting the AV tension.

Tuning with excessive timing at idle can certainly lead to a lean condition, which will give you the transition bog. Setting the timing back will only get you to a place where you can retune, probably won't solve the problem by itself.

You may indeed have two problems. Happy hunting!

 

Your accelerator pump on the carb isn't working properly. I'll put $50 on it that I'm right. Anyone want to bet against me? Well, that's my guess anyway- not really very sure, actually.

Seriously, my brother had an 81 T/A with a QJet and he DID get T-Boned on Rt. 1 near where we lived. That happened 2 days before I was going to rebuild the carb for him. I mean the car was HORSESHOE shaped and the driver's window was broken out where he put his head through it. Oh well, stuff happens.

How toknow this is the problem- air cleaner off, looking down the primary venturs open the throttle by hand (engine off) and look for 2 little streams of gas shooting out as you open the throttle. Try it by really cranking the throttle open quickly and then again a little slower. Sometimes they work OK when you mash it but not when you just slowly step into it.


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94 Firebird Formula M6- No options but Z rated tires. No mods over $10. 13.5@105.
79 Malibu "beater" w/junkyard 400 SBC, tweaked QJet 4bbl, finally a decent set of heads, a few other tricks. A maddening 13.000001 @ 108 on the motor with little traction. No nitrous runs with the new heads yet.
Grandma's old 78 Malibu (33K miles!) soon to have the powertrain from the 79 put in it.

"One of the last remaining QJet tuners on Planet Earth!"

 

I'll take the 50 bucks right now I've gone through 2 brand new accelerator pumps in and both squirted a hell of a lot of fuel. No plug passageways on that circuit. Didn't get a chance to mess with the car today, working on painting a dually for the next few weeks. Over the weekend I'll have some time though.

 

lol @ Damon losing $50...hehehe
I didn't jump at the acc. pump theory just cuz he said it ran better when it was cold. Made it seem more like a CCCS problem.
Damon, do all 2nd gens end up getting T-boned. Thats how my 79 bought it, t-boned by a tractor trailer. Pushed my drivers seat through the center console, and the B pillar was bent in so far that the T-top was pointing straight up in the air.
...ed

 

Well, I DID say I wasn't sure. And yes, ALL second gens die by t-bone!

OK, this one's got me pissed off cause we should really be able to figure this one out. I LOVE mysteries but not when they go on TOO long. I'm on a MISSION to fix your problem now, man!

First off, we need to figure out if it's the PRIMARIES or the SECONDARIES that are the problem. Disconnect the secondary throttle linkage from the primary by taking the springs and such off the secondary throttle arm MAKING SURE YOU REMEMBER HOW THEY GO BACK ON. There are 2 springs and they aren't tough to get off (you don't even need a screwdriver). Once you do, take off the secondary throttle arm and disconnect the pushrod that activates it from the arm. Put the arm and springs aside and use a loose zip-tie to hold the pushrod out of the way but still allow it to move. Now take a drive. You are ONLY using the primaries at this point. Does the problem go away? if so then we have narrowed it to the secondaries. If not, its on the primary side of the carb.

This shouldn't take more than 15 minutes to try and considering the work you have put in already it's time well spent.

 

I don't know how the secondaries would come into play if I'm only pushing the gas pedal down maybe 1/2 to 1 inch. The lean spot/bog/stumble whatever you wanna call it just gets a lot worse if I take off from a dead stop at WOT.
I'll come back here Saturday night and report on what happens though. I'll try your idea plus, change the timing to factory specs, and possibly change out the distributor and carb for a non computer setup.

 

Ok, I tinkered around with the timing today and didn't see any improvement. Couple of things I noticed though were... When the vacuum connection that hooks to the air cleaner assembly for the hot air servo was left unplugged, throttle response was better than when I held my finger over it. More air getting in to the carb right? Ok, the second thing I noticed, when burping the throttle, a puff a black smoke comes out the tailpipe... ahh rich mixture! Could a higher rate spring on the accelerator pump cause too much fuel to be pumped out? IE temporarily flood the engine. Think I may try a softer spring just for the hell of it if they are available. The idle mixture screws are out 2 1/2 turns each. Can't do any test drives yet though seats are still in the upholstery shop.

 

Deactivating the Thermac system (hot air intake) will give you slightly better throttle response only becuase you are getting colder, denser air into the intake. It will also allow carburetor icing problems in cold weather.

A higher rate spring on the accelerator pump (I don't know where you got one of those) would increase the RATE at which the accelerator pump puts in fuel, but not the overall quanitity per accelerator pump stroke. In short, I don't know it that might be the problem. To check just disconnect the accelerator pump push rod temporarily and try it again. You should still get a bog, but for an entirely different reason- a LEAN stumble on quick throttle opening.


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94 Firebird Formula M6- No options but Z rated tires. No mods over $10. 13.5@105.
79 Malibu "beater" w/junkyard 400 SBC, tweaked QJet 4bbl, finally a decent set of heads, a few other tricks. A maddening 13.000001 @ 108 on the motor with little traction. No nitrous runs with the new heads yet.
Grandma's old 78 Malibu (33K miles!) soon to have the powertrain from the 79 put in it.

"One of the last remaining QJet tuners on Planet Earth!"

 

Sounds similar to my problem, but mine happens when it is cold and goes away when warm. I just reciently put in a can of gas treatment and it seems to be a lot less of a hesitation these days. I can't say for sure that cured my problem though.

Did you say this problem started after you had the engine rebuilt or just the carb? Mine started after the engine... I have some concerns about going to a lighter spring on the primary rods to acount for a longer duration cam.

Could it also be a bad oxygen sensor? If it isn't heating up right then it may cause a rich problem right?

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock... all the suspension stuff... 9-bolt posi disk is in... K&N filter... 93 octane...

-=ICON Motorsports=-

 

Damon, the whole air cleaner assembly was off with me just plugging and unplugging that vacuum port with my finger. When plugged, the throttle response from just flicking the throttle linkage at the carb was worse than when left unplugged. I couldn't drive the car due to having no seats (should be done getting upholstered Friday) I was thinking of using a LOWER rate spring for the accelerator pump so it doesn't squirt the fuel in as quick.

Biochem, the engine and carb were rebuilt at the same time. I had also put a new O2 sensor in before firing it up the first time. I'll put another new one in just incase when I put the headers on in a week or two. Just too busy right now trying to paint a dually.

Damn I miss driving the car even if it does run like crap lol.

 

In that case I think you're just seeing the effect of having a vacuum leak offsetting your over-rich problem slightly and improving throttle response. It's not the problem- just another indication of this strange over-rich condition.

Is this still the computer controlled QJet on the engine? They default to full-rich if they are not working right (not receiving signal from the ECM or the ECM isn't sending the right signal). Also, whoever "rebuilt" the carb could have messed up one of the many settings (like the IAB valve) that could throw the mix way off. Are there any "cvheck engine" codes stored in the computer?

Don't play with the spring on the accelerator pump- if its the stock one that came in the rebuild kit it's not the problem.

 

Yes it's still the stock Q-jet with the computer hook ups. I rebuilt the carburetor and the smog shop checked and set all the settings trying to track down what the cause of the problem is. Right now my check engine light is on and can't get into diagnostic mode for some reason using the paperclip method like I had before. Still don't have my seats back from the upholstery shop after a week and a half so I can't take it to a shop and have them plug in a scanner.
It hasn't been driving any different since the light has come on, btw the check engine light flickers sometimes :/ grrr more damn problems. Probably a couple simple things like corroded or pinched wires.

 

You've got computer or electricl problems. Chances are the problem is nothing mechanical in the carb. You HAVE TO get the ECM workign correctly (spitting out trouble codes) or it may be the problem itself. A lack of any response to dump the trouble codes is a bad sign that the ECM is having problems. The cehck engine light should never "flicker"- ON solid or OFF solid, but never flicker while the engine is running.

Getting a scan tool so you can see what the ECM is seeing is extrememly important for getting the the root of the cause quickly. You could throw parts at it for weeks and never figure it out.

The reason things are OK when the engine is cold but the problems happen when you warm up is becuase after the engien warms up the ECM goes into "open loop" mode where it starts looking at the O2 sensor and adjusting the fuel and spark curves based on various sensor readings (versus a pre-programmed set of tables when the engine is cold). That's when something is starting to lie to the ECM and then the problems start.



[This message has been edited by Damon (edited October 12, 2000).]

 

I think you mean it is open loop until the engine warms up, then goes to closed loop.

 

Got my seats back finally so I'll be taking the Camaro to the shop this week. Ahh it was good to drive it again after 2 1/2 weeks. Any ideas on how much a new ECM would cost if it comes down to that?

 

five7- yeah, what you said. Got 'em backwards.

 

Ok, little update. Finally got it to go into diagnostic mode and it shot out a code 51 PROM error plus the normal code 12. Ah good, only a 40 dollar part and about 15 minutes of work. Ordering it Monday to see what happens