I have a 1987 Pontiac Trans Am with a 350. It runs fine until after about 10-15 minutes after it warms up, then it will stall while driving normally. Sometimes it seems to be running rich, because of the smoke coming out of the exhaust, sometimes it seems to be running too lean, but I'm only assuming that because of the LACK of said smoke. The car doesn't overheat, and I've insulated to fuel line near the engine block to maybe help prevent vapor lock if that's the problem, but it still does it (I guess maybe the next step in that case would be the old coffee can trick). The electric choke doesn't work, and when I bought it it was zip tied open, and still is. I don't know if the carb is a CCC or not, and I don't have numbers, just a crappy pic taken with a cell phone in bad lighting when I had it pulled out of the car this summer (attached).

If it is a CCC, could it be a bad TPS or fuel air mixture solenoid? Or is it the choke, just in need of a tune up, or something else? Thanks.

 

well, there was no carbed 350 available in 1987, im not even sure they even did the carb 305 still, so you have some kind of "custom" job. better post a pic of your engine so we can see what you are working with.

 

Well, I'll put it this way:

I was only TOLD it was a 350 in the ad for it. Could have been a typo, maybe just ignorance. (As far as I know, in 1987 they still did make a few 350 carbs, but the GTA had fuel injection, and this is no GTA.)

It could be a custom job, they said the engine had been rebuilt... don't know if it's original. The engine does have a plate on it with some engine shop's name on it though. I ran the numbers on the carb this past summer, it said it came off of a Cadillac 307, so this could be a mystery.

 

It's a computer controlled QJet in the picture. Are the mixture control solenoid (blue 2-wire plug on the top) and the throttle position sensor (white plug on the front/driver's side) hooked up? Definitely won't run well without those.

Also, somebody has removed the vacuum canister that goes on the front/pass. side as well as the rod that goes from that canister back to the secondary air valve doors. Will definitely cause a bog when you go wide open without them.

Only factory carb'ed engine in 87 was the LG4 305.

 

All the wires are hooked up, and I've even gone through all the underhood wiring and added any plugs and connectors and stuff that had been cut out previously and hooked everything back up stock.

As for the vaccuum canister and rod, I've also been trying to reattach everything else that had been taken off, and I didn't know about that, so I'll get on replacing that as well, although I don't think that's the source of my problems, but thanks anyway.

 

Most likely it is a 305. When the ad says "350", flags should go up, because you can't tell the difference between a 305 and 350 by looking at them. Saying it's a 350 means you can get more money out of it, and most of the time buyers don't know how to verify which engine it is. For the record, you need to get the casting number off of the block to tell.

Is the SES light coming on? If it is, you need to retrieve the codes from the computer so you know what to go look at.

Nothing you described matches the symptoms for vapor lock. But, 87's did have an in-tank electric fuel pump along with the mechanical pump mounted on the engine. The in-tank pumps are prone to failure, and when they do, it can cause fuel delivery problems. The computer doesn't have any way of knowing that, by the way.

It's painful to hear of chop jobs like this, people who don't understand how something works thinking they can improve it by removing things. Good luck finding the link that goes from the front vacuum can to the secondary air valve - you might be better off getting a professionally rebuilt carb and turning this one in for the core.

 

No lights are coming on unless I hook up the wire to the electric choke... then the "Security" light comes on (wtf? )

But I didn't even know there was an in tank pump at all. Looks like checking that out is my next step, although I won't be able to start work on it until this summer.

Thank you very much.

 

You GOTTA have the choke hooked up. Without power to the choke it will often not open fully just from radiant engine heat. And the sometimes yes/sometimes no behavior can result.

Power to the choke system is more complicated than you might expect, electrically speaking, although it shouldn't light the check engine light. The choke/oil pressure light is tied in with it, however. And even a bad alernator can light it up. I believe there is a sticky at the top of this forum with more information about the choke's power system.

But no matter what, you still have to have power to the choke so that it opens fully or your tuning will end in nothing but frustration.

 

I am not an expert on the quadrajets but I sure have had a lot of them. My suggestion is to first find out what engine it is then have someone who knows quadrajets to rebuild it and then make sure its hooked up accordingly. I have heard of people calling them Quadrajunk. I disagree. You just need someone with the knowledge to rebuild them right and know how to hook it up correctly to the engine it is to go onto.

 

It wasn't the Check Engine light, it was the Security light, which is even more confusing/frightening. I'm going to figure all that out this summer, though.

 

Ok, regarding the bad electric pump, the mechanical pump can't keep up with the fuel demand and that would starve the engine for fuel correct?

And regarding the fact that it also occasionally (VERY RARELY) runs rich, a bad coolant temperature sensor for the ECM, which causes my fan not to start when the coolant gets up to temperature, could also make the ECM send a signal to run rich because it thinks the engine is freezing, correct again?

The original fan relay was completely bypassed by the PO, I hooked it up again, but the ECM doesn't flip the relay for the fan relay's ground, causing the fans not to start, so I figure the sensor's gone and that can be a source for part of my fuel problems as well. The electric choke doesn't help this situation but I think I'm making some major breakthroughs with my old TA now. I'll be back on the road this summer for sure.

 

When the electric pump is non-op, it causes additional restriction in the pick-up that the mechanical pump can't handle. If the pump wasn't there, the mechanical would be fine (but the system would be more prone to vapor lock).

The ECM doesn't control the radiator fan on carb'd cars. That's a switch in the passenger side head. It grounds a relay when the temp gets over 238 degrees F to power the radiator fan. If yours isn't working, check that switch and circuit. There is also a fuseable link in the fan power circuit.

 

Alright... so just check the fuel pump then, eh?

 

X the Carb, if you have the money and you don't have nitt picky smog laws in your town, do some research on what you can do to your car, and perhaps convert your car to mechanical advance timing, (don't know the proper term) ... personally, I have had nothing but trouble with my Qudrajet carbs... bought many through Kragen auto parts, which were rebuilt by Holley, also had a couple rebuilt by reputable shops... they'd run great a few months and then crap out... there were too many "FRENCH WORD FILLED DAYS" ...

 

Very bad advice.

 

Maybe it's just me, but I love my Q-Jets, cc and non. I have always had excellent results with them. It may be just my opinion but, a properly dialed in Q-Jet will give many more years of reliable service that any other carb available. If it is possible, (I'm sure it is) it is best to get the car back to the original, legal, configuration and experiment from there. I know these computer controlled carb cars can be a pain, ( I have one) but when they are in a proper state of repair they are a blast to drive. My 87 Formula's in-tank pusher pump is still working after 23 years! This is an easy thing to check. Pull the round connector at the oil pressure sending unit and jumper across the terminals of the plug. You should be able to hear the pump and hear the carb making gurgling noises. No reason to drop the tank if you "think" the in-tank pump is bad. The other things to look for are the vacuum lines and the egr valve and egr valve solenoid. Best of luck with your project.

 

Check with these guys. http://www.carburetion.com/quadrajet.asp

 

Buy a beat-up junkyard QJet and swipe the part off it. That's the good thing about QJets- you can buy a box full of them for $20.

 

I concur!...but junkyards around my place charge closer to $30 for a Q-jet. Still worth it though, I think.