84 15th TA runs good cold but falls flat after warmed up?? - Third Generation F-Body Message Boards

rare15thtransam · 10-08-2009, 11:52 AM

I have a 1984 15thanniversary Trans Am with 305HO with the electronic controlled carb! It runs great when its cold once it warms up it falls flat on its face under acceleration! I already put a new MSD cap and rotor and plugs& wires I think its the carb! I have a brand new edelbrock carb so I bought a adapter plate and installed it! It ran great but the engine light comes on due to the electric controls are disconnected it work great for a day the next day I went to let it warm up it ran great for about five minutes then it started running rough and if you tried to rev it up it just died! I thought it was just the choke so I rewired the electric choke and tried again same thing ran good for five minutes then died! Please help

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Atilla the Fun · 10-08-2009, 12:01 PM

You may be losing all your spark advance, or you may be running out of fuel, or it could be both. PM five7kid about which Carter fuel pump to get, because you'll be needing that soon if not now. Check how much advance you're getting up at 3000 rpm with the engine warmed up, then report back.

rare15thtransam · 10-08-2009, 12:24 PM

I also replaced the fuel pump so It gets enough fuel so I was wondering if the edelbrock would even work since the original is computer controlled! The computer is suppose to adjust the timing and fuel and air mixtures so I am looking at buying a rebuilt quadrajet as far as checking the advance of the distributor it wont stay running once it starts to warm up and I don't know how to check please tell me how!

Atilla the Fun · 10-08-2009, 12:31 PM

first, you seem to not understand that even when your car was new,the stock fuel pump was NOT able to keep up, and the same goes for the one you got from your local auto parts store. If you try something like a chrome Holley pump, it has no provisions for the return line. So you need the Carter. As for the timing, you can't see if you're losing advance just by looking at the check engine light, because the light came on anyway when you swapped carbs. So now you need a dial-back timing light. It should be reading over 30 degrees of advance at 3000 rpm. But since you swapped the carb, the computer is probably in limop-home mode, pulling timing. If you're going to run a non-computer carb, and there's no valid reason to do so, then you must alaso replace your distributor for a non-computer version. Have the Q-Jet remanufactured, for around $350, then reinstall it and that will solve all the problems not related to the fuel pump. The non-computer stuff has NO advantages. If you want performance, start with a better intake manifold, not a worse carb.

rare15thtransam · 10-08-2009, 12:41 PM

I don't know much about chevy 305 this is the first chevy power plant I have ever owned so the lack of info is why I am here! I only tried the edlebrock is I already had a new one for my 46 ford truck and I don't have the money to buy or rebuild the quadrajet so I figured it would work but at least with the quad it would run good for an half hour or so but then it would fall flat on hard acceleration and start to cut out at 55 I plan on getting a rebuild quad just don't have the $$$ right now.

3rd gen Will · 10-08-2009, 01:22 PM

I suspect the coil.

I would check the resistance in you coil when it starts to run badly. The resistance in the primary circut can increase when the coil heats up causing you to have a weak spark and it would result in the car running poorly when the car has been running for a while.

Unless you run a mechanical/vacuum advance dist with the edelbrock you will have fuel mileage and performance problems. If it runs good cold it's probably not the Q-jet, I'd put it back on to get the computer back in closed loop.

rare15thtransam · 10-29-2009, 12:13 AM

I bought a rebuilt factory carb and new egr valve and it runs like new and it can lay a nice block long set of black marks! It would barely chirp the tires when I bought it now she really hauls thanks for the input!

3rd gen Will · 10-29-2009, 11:42 AM

glad you figured it out!

rare15thtransam · 11-03-2009, 01:32 PM

Well the new carb works great but my car still stalls after driving it a while today I drove 35 miles on the highway no problem after I got in town at the stop light it died then I started it back up then it was running rough the idle was bouncing from 1000 to 1500! Every light I came too it would stall out and if you tried to step on it it would fall flat again! What could cause this my carb, egr valve, cap, rotor and wires are all new! Could it be the coil is going bad what ever it is it only happens when it is warmed up to full op temp! Please help this is driving me nuts!!!!!!!!!

Gumby · 11-03-2009, 02:24 PM

Id go backwards on it, put back regular type carb but re-do the ign system too ,a new vac dizzy n MSD controller box.[if your broke, buy Summit stuff over Mallory stuff, Summit stuff is just Mallory with a diff sticker and cheaper. BUt MSD is king] Take all engine managment out of the hands of that stone age computer system.

Or start tearing into the computer system.

rare15thtransam · 11-03-2009, 11:00 PM

Maybe if I just reset the computer it will help I don't know I have never had this problem before it almost acts like it isn't getting spark all the time after it is hot maybe it is vapor locking?? I don't know what to check for next any ideas without replacing factory stuff with aftermarket ??

Gumby · 11-03-2009, 11:46 PM

Quote:

Originally Posted by rare15thtransam

Maybe if I just reset the computer it will help I don't know I have never had this problem before it almost acts like it isn't getting spark all the time after it is hot maybe it is vapor locking?? I don't know what to check for next any ideas without replacing factory stuff with aftermarket ??

You need a computer expert, Im old school and when the fancy new stuff works its great but when it don't and nothing make sense on what wrong, its the first thing to go.

With a car like that, you could probably pick up performance going that way.

Doing that with my 2.8 Bird is gonna lose power but Im sick of the money pit computer stuff.

3rd gen Will · 11-04-2009, 03:55 PM

I am assuming you never ohm'd the coil like I suggested? That is the first thing I'd do, get it warm and check the coil's resistance. Instead of throwing parts at it, checking the coil doesn't cost you any money and it can rule that in or out as a problem.

rare15thtransam · 11-10-2009, 03:45 PM

Quote:

Originally Posted by 3rd gen Will

I am assuming you never ohm'd the coil like I suggested? That is the first thing I'd do, get it warm and check the coil's resistance. Instead of throwing parts at it, checking the coil doesn't cost you any money and it can rule that in or out as a problem.

I did check out the coil it is new I replaced it when I did the tune up so I put the original back in same problem! The car runs perfect and has great power from idle through the rev limit after driving about a half hour it starts acting up and missing bucking and bogging out with no check engine lights the temp is around 200 and the oil pressure is at 60 psi I am running out of ideas so anything you might have would be great!

rare15thtransam · 11-13-2009, 12:33 AM

I called one of my local shops and they told me that they have seen bad distributors on the 80's Camaro's and Firebirds with the electronic controlled carb and advance! I don't know what else to look for please help!!

rare15thtransam · Yesterday, 11:24 PM

Still can't figure this thing out Here is a list of all the new parts, New carb, new coil, cap, rotor, plugs, wires, fuel pump, EGR Valve, pcv, ignition control module and capasitor in the distributor, and oxygen sensor! I got a check engine light and it said O2 sensor and ignition module so I replaced both and still stalls and falls flat after 30 minutes of driving! Please Help I have no more tricks up my sleeve! PLEASE HELP