Hi all,

My 85 trans am is acting up quite oddly now and im dead stumped.

The car will free rev no problem, and when you drive nice and slow it runs great.
NOw heres odd part, when the gas is pressed to floor to pass a car or just to get on it, the motor stumbles on its face and "pops" and runs like absolute crap!

I have changed the fuel filter, fuel pump and am running 89 octane in it. It seems when the secondaries opens up it bogs and runs like crap. I am running a open element air cleaner and full exhuast...........

also, when tryin to burnout it does same thing....runs out of power and craps out...........

ANYONE have a clue????????????//////

Thanks, SHLEBY

 

Did one of the secondary rods fall off the hanger? Only 2 minutes of work to check that!

 

Primary metering rods stuck, not coming out of primary jets when vacuum goes low, like when you open the throttle.

 

Okay....i know how to check the first thing....i think
those are the two rods hooked the secondary flaps on top that vacuum hold shut at idle. Then they open open when the secondaries open up....right?


How do i check for the primaries????? or do i have them mixed in my mind?

Pictures or a write up how to fix this would be awesome......i havent messed with q-jets before.....

 

Yes, you're on the right track with the secondary rods.

The other thing about primary rods sticking in the down position only applies to earlier non-computer controlled QJets where the primary rods move up and down by a vacuum-operated piston in the main casting. Not applicable to your computer controlled unit.

 

so how do i checkk them then? i hear clickin for about 5 sec's before i start it then it stops and i crank car. Runs really good if you stay out of throttle hard.

 

Generally speaking, if it's clicking it's working! The clicking is the primary rod piston hitting against it's upper and lower stops under the ECM's control. It cycles about 10 times a second.

 

okay cool, thanks

i messed around and noticed someone bent the tab so the upper flap over the secondaries will open farther than stock.......is that bad? A friend gave me a brand new cc-q-jet that needs cleaned so i guess it isnt such a big deal.

But thanks again Damon and rebuildman

 

Bending the tab is a common mod and shouldn't hurt anything. IT sounds like you need to adjust your MCS dwell using a dwell meter. If your primaries aren't enriching properly, the car will do exactly as you describe. The secondaries alone can't overcome an over-lean primary condition when you step on it.

 

i have an 85 berinetta that does the same thing only mine has a slight bend in the fuel line from pump to carb.

 

mine was doing the same thing. I replaced the crb with a used one and problem solved. I guess the castings were leaking?

 

I wouldn't bother checking the MCS myself. If it idles fine, that's probably fine also - assuming the timing and idle speed are set properly. It doesn't sound like a primary problem to me. -Silly question I know, but have you tried adjusting your secondaries (spring)?

They may be opening too early or late, causing either a lean or rich condition causing it to stumble or "pop". I've seen it more than once. The stumble is a dead giveaway I think. - Or maybe I'm not understanding the problem...

 

I have everything set to spec relating to idle and timing.

The car runs amazing until the secondaries open im guessing, like i said before it will run like a champ until you slam the gas and then it shows its ugly side. Also, it shifts early(4000-4200rpms)

I have noooo clue how to play with q-jet secondaries lol! Do tell though please.

It'd be nice to be able to "punch it" and pass someone on the highway without having to "roll" into the gas slowly.

The car has edlebrock aircleaner, acell plug wires, acdelco plugs, hedman shorties, hedman y pipe, 3" hi flowcat, 3" edlebrock sdt catback.

See list and see what you think.....oh also the motor/carb/trans are original at 155k miles LOL!

 

There's a sticky in the top section of this forum with the GM instructions, and a tech article linked from the thirdgen.org homepage about making the secondary adjustments (link to the tech article is contained in the "Welcome...Please Read" sticky on this forum).

A bad choke pull-off (vacuum break, in GM's language) will cause a bad bog on q-jets (one of the reasons they got that pejorative nickname - people would remove the pull-off and wonder why the carb started behaving unacceptably with this "improvement").

Also make sure the secondary metering rods are pulling up when the secondary AV is opened up.

 

hey thanks for info guys! i did notice the lil mechanism that locks out the secondaries during warm up not working correctly so i tied it out of the way so secondaries would open. That solved A LOT of the popping and hicups.....ill doing some reading thanks to five7kid! i hope i can get this carb fixed, cc-q-jets are the best carb for a sbc

i mean when have you heard a sbc run on e-way and get 25 mpg????? and it adjusts it self.....i mean come on! I love it!!!!! i need to find a few for backups....im in process of putting them on my other car/truck!

 

I second the secondary metering rods. Sounds like you're getting a lean pop, probably caused by lack of fuel as the secondaries and air valves open.

 

last time i checked(when putting car together) seemed the two rods moved as one unit.....ill check again

 

Nope, the car can idle fine even with a very badly adjusted MCS. It not only has to provide the right mixture at idle, but it also has to have enough range to enrich under heavy acceleration. Always check the primary circuit first, because it is still providing a critical function even when the secondaries are open.

 

Yes sometimes I get my best idle with the TPS disconnected, MCS full rich. Could very well be a transition issue from primaries.

I'm personally invested in the secondary metering rods, however, as I've recently experienced a failure of the secondary cam in my daily driver (got 27 mpg on a recent trip with the secondaries locked out). Would be too weird though for it to happen to someone else at this time.

If he doesn't have a dwell meter a simple test may be a few turns in on the IAB or a few turns out on the idle mixture screws followed by a test drive? Would temporarily enrichen the primaries but you'd still have to come back and properly set with a meter, unless there was no change and you went back to original settings. Butttt, you couldn't be sure you enrichened it enough or maybe provided enough enrichment to mask another problem.

If the dwell shows good and the action of the secondaries and air valve/choke pull off adjustments do no good, I'd open it up with a rebuild kit. Clogged passage, trash, something blocking or restricting fuel flow to secondary circuit.

 

holy crap!.....im sooo lost.....maybe this is why people go holley/edelbrock

 

Verify that the two secondary rods lift up as the air valve is opened, the action should be smooth. Check the tension on the air valve and you may want to set it per the instructions in the tech articles.

At a great risk of oversimplification:

A lean pop may occur when the secondaries open and not enough fuel is introduced. The motor will 'pop' thru the carb and stumble. If it's not getting enough fuel it will not normally pick up and continue running unless the throttle is backed off. Secondary rods that are not coming out of their jets can cause this.

A bog is an initial hesitation to a large throttle opening. The motor will stumble as the throttle is quickly opened, hesitate and then take off. Bogs are usually caused by opening the air valve too early. Too much air/fuel too soon.

Check the rods and get back. It's not really that complicated.

 

okay secondary rods are attached and moving.

i made a vid of car.......dont mind me on camera.....http://www.youtube.com/watch?v=7xvmhXVfbE4

also, i have exhaust off for some work....hence why it sound like crap. shorty headers and a 2.5" y-pipe....thats all! when this etup was in the 83 firebird it ran so much better!
http://www.youtube.com/watch?v=WkUibMrNoJc
^^^ and that is 83 firebird^^ all i did was swap motor/trans from one car to other!

 

I noticed no one mentioned searching for a vacuum leak. I had a similar problem with my car, ran fine if I didn't mash the pedal quick, but as soon as I did it would stumble. Turned out I had a vacuum leak through my intake gaskets. Try disconnecting all the vacuum lines except for the MAP sensor, brake booster, and PCV valve from your carb and use plugs from the auto part store to cover them. Also have you checked you're plugs lately? 90% of the time problems can be ignition related. Even if its not it'll show another symptom, running rich or lean or in my case oily.

 

The motor ran fine before the swap? and nothing else was changed-same carb, intake, ignition system, etc?

If that's the case I'd lean towards fuel flow. From the vid it appears that it's just dying off at a high load and not recovering until load is reduced?

Check your filter. Swap could have introduced trash into lines. Make sure there are no kinks in the line. Stock steal line from pump to carb still?

Pump output can be checked by pulling the line at the carb and letting it flow into a container for a measured amount of time. The engine will idle for a few minutes with just the fuel in the carb. Same fuel pump?

 

EVERYTHING is same from the other car lol, i mean from the 83 wiring harness/ecm to the fuel pump.(85 harness was MIA for motor)

Motor does that only when stomping it, if you notice later it the video(1st one) i showed that if you pull rpm to around 3000 rpm, then hit gas it will pull to redline with no problem!

It does have stock metal line from pump to carb, previous owner messed it up though. The fitting was froze to itself and he just cut the line so he could get the fuel filter! But it has rubber hose slipped over the spot where it was cut and double clamped.......maybe turbulence is problem? I dont know.

Ill have to check filter. I put a new one in the carb before finishing the swap. Also, i hooked a generic electric fuel pump up to the lines before putting motor in and flushed gas tank about 10 times because car had sar for about 10 years. I put it though screens and sold that gas to a friend so i wouldnt get bad gas(he drives a kia.....who cares.


Also, watch the 2nd video....that was days before the motor swap out.....car ran great!

 

Probably not a fuel delivery problem then. Go back to your choke pull off and air valve settings adjustments.

Check your pull off by removing the small vacuum line to it, depressing the plunger, plugging the vacuum nipple with your finger and ensure the plunger remains depressed.

The tech article will walk you through the air valve adjustments for spring tension.

If these checks don't help it may be time to get a dwell meter and/or open it up. Unless, of course, someone else chimes in with another opinion...which would be welcome.

 

http://www.youtube.com/watch?v=o2cOmQRoIac

listen around .26 into video and listen for the misfiring to start......
THATS NEW! what the crap??????????????????

it starts misfiring when it gets warm.....................HELP?

 

Have you looked for a vacuum leak? Pretty easy and cheap way to do.

 

Vacuum leaks typically cause low speed problems, not WOT.

Might still be fuel. The pickup could be clogged, or there's a smushed line somewhere upstream of the pump. If the engine has been out, over the transmission is a vulnerable place. Or an old rubber line upstream of the pump could be collapsing.

Make sure the air cleaner isn't doing anything funny. I had mine on a little crooked once, jammed up the choke & AV linkage.

 

Ill check lines tomorrow.

air clean sits above everything on carb so it doesnt come close to choke/av linkage. Its a triangle style edlbrock one......yes the cheapie one lol.

Im guessing carb, because i had switched carbs once from a cc q-jet to a non cc q-jet and car ran just amazing! Then i had swpped carbs back and car still ran amzing.......then this