Toyota h8r

hi all,

figured id pick everyones brain before i start digging into my z28. I bought the car and knew it has rough idle that was also high.

--Idles around 1500rpm when warm and is rough.

--at light part throttle to maintain speed the car bucks heavily, but as SOON as you ease on the throttle it smooths right now.

--has spark knock over 90% throttle(appox)

--car has hard restart when hot(vapor lock probably)



car is BONE stock cailfornia emission LG4 with 5 spd. Previous owner went thought and put new ccc quadrajet, cap/rotor, plugs, and wires.

im thinking the car is out of time or vacuum leak massively.

car runs great at part throttle acceration, but at WOT or cruising low rpm it pops and buck

five7kid

iTrader: (14)

Not sure how massive the vacuum leak would have to be, but those are my first two guesses.

Toyota h8r

Well it started before tune up and new carb so im kinda lost since a myriad of parts were thrown at it. Literally everything to my knowledge gas been changed except ecu.

Maybe a a worn distributor gear? My dads vortec did it in his truck but not this badly.

Check engine comes on after a WOT pull...I need ti check timing and see if its within spec

Damon

First thing I'd tackle is the obvious- the high idle when warm. The QJet has a fast idle linkage built into the choke system. It raises the idle speed any time the choke is on. The usual issue with a high idle on a warm engine is that the choke isn't pulling off fully. This is usually the result of the power wire to the choke either being flat-out disconnected (often the connector is mutilated) or it isn't getting power (choke relay bad or who knows what else). It's a single wire connector that plugs into the terminal on the round, black plastic thing on the passenger side of the carb (the choke element).

Running around with the choke partially closed is a sure-fire problem-causer. That's what I'd check first. I dout that's all that's wrong but that's where I'd start.

I'd also make sure all the other electrical connectors on the carb are attached as well- Mixture control solenoid (2-wire blue connector on the top/front of the carb), the Throttle Position Sensor (white 3-wire connector on the front/driver's side of the carb) and the A/C compensator solenoid (singe wire connector going to the round canister hanging off a bracket on the the front/driver's corner of the carb).

Toyota h8r

Well found a little out.

Few wires are crossed and touching, now miss for most part is gone.

Mixture screw cover is missing and when sprayed with either motor rises in rpm. So im assuming it needs a gasket for manifold.

Carb was loose as well......doesn't seem to go into closed loop and fan isn't working either :/

Oh and 93 octane seemed to lessen spark knock almost completely so im assuming timing is off. Maybe caused by bad ign module?

Thought this car wouldn't be a project but it is now lol

Toyota h8r

http://m.youtube.com/watch?v=JNS7VymkJ-Q
bad video from my DROID x2 but you can see how motor hunts and runs like crap

Im starting to hate q-jets again lol

Camaro305SB

Don't hate the carb, hate the guys that tried to tune it and failed.

I'd listen to the above posts about the choke also check for vacuum leaks and make sure its timed right. My 87 LG4 auto is "0" degrees with the 4 pin connector unplugged. Very easy to verify timing and choke operation.

Toyota h8r

Im pulling intake and electronic qjet off and storing it in the trash lol.


Going to std qjet and edelbrock intake with vac advance distributor.


I had 4 guys come look at to see if I was missing something but everyone agreed that my two carbs are junk.

Camaro305SB

Well personally I don't agree with that but do what makes you happy. People are just afraid of Q jets because they don't know anything about them. I'll take the carb and diz if your trashin em. :-)

Toyota h8r

If I were keeping it bone stock id keep em but electronic qjets fight be everytime. I've had 3 vehicles with electronic qjets and never had success. I've tried new carbs......rebuilt......everything. they always run like crap.

I swap a standard qjet and hei dizzy on and they run amazing after.

five7kid

iTrader: (14)

My experience is exactly the opposite.

Like already said, don't trash them. Someone can use them.

Toyota h8r

Five7kid believe me im trying ..

.....3 ecus, 2 carbs, intake gaskets and egr valve..
.

Camaro305SB

I don't want to make any assumptions but it sounds like you may need a more experienced helping hand. The carb issues sound like bad rebuilds or adjustments, intake gaskets are problematic on ALL GM cars, and EGR failures usually because the ports are clogged up. A little patience goes a long way and theres plenty of knowledgable fellas on here that are willing to lend their advice. If you decide to go full mechanical I've been told to use Holley as they are pretty simple to tune up. My carb knowledge is actually limited to the Rochester Qjet.