Okay, I have NO CLUE what is wrong with my car. I have tried everything I know, so please help.
Heres the problem:
My car idles pretty rough, and wants to stall.

Heres what I have done:
1. Checked distributor for carbon track.
2. Replaced plugs and plug wires.
3. Replaced O2 sensor.
4. Did compression check - all cyls were 155 psi
5. Tried changing timing, didnt help, but I retarded it a bit to compensate for this condition.
6. Checked entire engine compartment for vacuum leaks.
7. Cleared ECM by disconnecting battery for 20 minutes.

What the hell is left? The only problem my engine has is that the valve guides and seals are worn, so some oil burns on startup.
I swear to god, if my ECM is bad, im pushing my car into the local lake and collecting insurance...


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1983 Pontiac Firebird SE
LG4-Based Chevy 400
700R4 Tansmission
Modified 4 Barrel Q-Jet Carb
Accel Super Stock 8mm Wires
Edelbrock Pro-Flo Air Cleaner
3.23 Posi Rear
14X7" Cragar SS/T Wheels
35X4 CD/AM/FM Head Unit
100WX2 Amp
2 Pioneer 12" Subs in Custom Box

[This message has been edited by Ward (edited July 20, 2000).]

 

The floats in Q-jets have a bad tendancy to sink so you should remove the airhorn and check the upper and lower levels and while you are at it replace the needle and seat. Q-jets are excellent carbs, but once you modify them you need to really know what you are doing to keep them drivable.

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bought a wrecked(head on,bad)'84 Z28 rebuilt it in'92 parked it in
'93 and ordered a '93 Z28. Got tired of the 4th gen in '99 and sold it and begin swapping in '85 TPI converted to speed density. engine is all stock except for comp cam. body has '86 IROC nose peice,ground fx and IROC wheels/goodyear 245/50's. IMO this car looks and feels more "racey" than my '93 did. and I love driving it. BTW fuel injection is great I'll never go back to carbs.

 

I did replace the needle and seat about 3 months ago when I rebuilt the carb, and when I cleaned it 2 weeks ago, the needle and seat were absolutely spotless, nothing wrong with them. Also, it started doing this about a month ago, it was fine for a long time, and jsut started this suddenly.

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1983 Pontiac Firebird SE
LG4-Based Chevy 400
700R4 Tansmission
Modified 4 Barrel Q-Jet Carb
Accel Super Stock 8mm Wires
Edelbrock Pro-Flo Air Cleaner
3.23 Posi Rear
14X7" Cragar SS/T Wheels
35X4 CD/AM/FM Head Unit
100WX2 Amp
2 Pioneer 12" Subs in Custom Box

 

I'd check out the MAP sensor. my friend's 4.3 S-10 Blazer was having the same prob today and we did the O2, nothing changed, did the MAP and it started up perfect. I know the MAP probably has a slightly different function on the LG4 than it does on a TBI motor like the Blazer, but they it wouldnt hurt to at least test it. His truck was running extremely rich and it would idle like **** and want to stall every time he let off the gas.

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350, Comp 262, Edelbrock Performer intake 600 cfm carb and exhaust, headers

 

Try checking the EGR valve. If it's stuck open the exhaust gases entering the cylinder at idle could cause the engine to stumble and die since the spark plug can't provide enough heat to burn the gases. I ran into this problem on my car. Just a thought....

 

I thought maybe it was the EGR last week, so I blocked off the EGR with a metal plate under the gasket. No difference. But I did not check the MAP. Do I even have one with an LG4 system? If so, where is it?

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1983 Pontiac Firebird SE
LG4-Based Chevy 400
700R4 Tansmission
Modified 4 Barrel Q-Jet Carb
Accel Super Stock 8mm Wires
Edelbrock Pro-Flo Air Cleaner
3.23 Posi Rear
14X7" Cragar SS/T Wheels
35X4 CD/AM/FM Head Unit
100WX2 Amp
2 Pioneer 12" Subs in Custom Box

 

yeah, on my 85 LG4, it was located above the distributor, a little to the pass. side. it should have a wire harness and a vacuum line running to it.

 

I think I have that. What does it do anyways, and why would it cause my car to run like this?

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1983 Pontiac Firebird SE
LG4-Based Chevy 400
700R4 Tansmission
Modified 4 Barrel Q-Jet Carb
Accel Super Stock 8mm Wires
Edelbrock Pro-Flo Air Cleaner
3.23 Posi Rear
14X7" Cragar SS/T Wheels
35X4 CD/AM/FM Head Unit
100WX2 Amp
2 Pioneer 12" Subs in Custom Box

 

on tbi/tpi motors i believe it has something to do with the mixture adjustment...but i'm not too sure how much the ECM adjusts the mixture in those electronic Q-jets. is there lots of black stinky *** smoke coming out of the tail pipe? if so you're running rich and you must find the cause for this, possibly the map sensor

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350, Comp 262, Edelbrock Performer intake 600 cfm carb and exhaust, headers

 

Have you completely disassembled the carb down to its component parts and soaked them all in carb cleaner (some one of the caustic kind, not just lacquer thinner), to remove any possible foreign matter from every internal passage? Have you epoxied over the spun-in plugs under the primary metering jets? Have you removed every single vacuum line from the carb & intake and plugged them, to make sure you don't have a mystery vacuum leak somewhere?

This may be somewhat more work depending on your situation, but have you tried a known good non-computerized carb and/or dist? That would certainly eliminate those components as potential causes. You wouldn't necessarily have to do a complete install to the point you could drive the car; if it idles terrible that's as far a you would need to go.

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"So many Mustangs, so little time..."

 

You know the VAC sensor (CCCS has a VAC not MAP sensor, same thing but in reverse) theory almost makes sense, except i don't see how it wouldn't throw a code. What the VAC sesnor is primarily used for is as a vacuum advance type function for the distributor. If the VAC sensor is bad or disconnected, your timing sits on the back bumper..leading to a very rough and soggy idle, part throttle. However, when this happens they usually toss a code prety quick, the computer can identify this problem pretty easily since no vacuum with a closed throttle and idle rpms just makes no sense.
You can test this pretty easy. Jumper into the middle wire of the connector and look at it with a DVM. With the car off you should see ~0V. Now hook a piece of hose to it and suck on it (or use a vacuum pump if you got one) and you should see the voltage go up the harder you suck. If not, it's dead. Sorry, but i don't know the voltage specs for what V corresponds to how much vacuum.
ed

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Ed Maher - Moderator @ the Carb Board
85 Z28 - 357c.i. - stolen 12/24
Click Here for the Rest
'83 Grand Prix - low miles
Only mods...Homemade open element, 2.5" cat and exhaust, CK-B metering
and the way out ******* style in effect
stock 14" wheels w/ wire hubcaps in front
snowflake 15" alloys in the back

 

Just a thought, you didnt start buying your gas at new place just before this prob. reared its ugly head did you? Too many gas station/convience stores purchase poor quality gas that has an unusually large amount of water in it. This is how they sell it to you cheaper.....

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bought a wrecked(head on,bad)'84 Z28 rebuilt it in'92 parked it in
'93 and ordered a '93 Z28. Got tired of the 4th gen in '99 and sold it and begin swapping in '85 TPI converted to speed density. engine is all stock except for comp cam. body has '86 IROC nose peice,ground fx and IROC wheels/goodyear 245/50's. IMO this car looks and feels more "racey" than my '93 did. and I love driving it. BTW fuel injection is great I'll never go back to carbs.

[This message has been edited by JAMES POLEDNA (edited July 21, 2000).]

 

I have not changed gas stations, thats not it. And yes, I had literally every part out of my carburetor soak in a bucket of carb cleaner, but they were all clean to start with. Also, i put the straw attachment on the carb cleaner can and sprayed it through all the fuel pasages to clear out any possible blockage. It seems like its running lean for some reason. No black smoke, but it seems to get better mileage... like its using less gas.

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1983 Pontiac Firebird SE
LG4-Based Chevy 400
700R4 Tansmission
Modified 4 Barrel Q-Jet Carb
Accel Super Stock 8mm Wires
Edelbrock Pro-Flo Air Cleaner
3.23 Posi Rear
14X7" Cragar SS/T Wheels
35X4 CD/AM/FM Head Unit
100WX2 Amp
2 Pioneer 12" Subs in Custom Box

 

Id go with checking the map sensor, and if all else fails you can call me up and i'll help you push the fu*ker into the lake!
bowtieguy01

 

Just FYI: The older cars had cheaper ECMs... I got an ECM for my 92 for like $130 and I heard the ECMs for some of the older carbed cars were half that.

 

Hey Ward,

If you guys sink it, can I have your tranny and seats? lol

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`85 Z28 5.0L TBI
Don't ever be:
Found On Road Dead!