Sporadic miss under a load...HELP!
Thread Starter
Burning Brakes
Joined: Jul 2004
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From: Sick of these TOOLS & AZZHATS in DC
Sporadic miss under a load...HELP!
Let me just start by saying...
Ok...now that I got that outa my system, here's my problem. Car starts perfect, idles great, revs to 4K+ in park great...out onthe road from low rpm (1000-1500) in any gear if I stab it it will accelerate with sporadic hesitation. If I'm rolling along at say 50mph and 2500 or so rpm and punch it, it kicks down like it should and does pretty well with no hesitation. (stock TH350 with 92K on it)
The motor is a new GMPP 383 with about 1200 miles on it. Here's what I have done to date to try and resolve this:
New plugs (AC Delco)
new wires (2 different sets - Belden and Moroso)
new coil, module, cap, rotor
Timing is all in at 32* by 2800 rpm (32 recommended by GM for Vortec heads-tried 36* as well with no improvement)
Carb is freshly rebuilt Qjet (Lars)
new mech fuel pump
tank was just dropped and cleaned; sock cleaned; fuel lines purged and all flexible fuel hose replaced with new.
WTF am I missing?? Could a failing torque converter of tranny be giving me these symptoms?? I am at my wits end with this damn thing. Any ideas from you "seasoned veterans"??
Ok...now that I got that outa my system, here's my problem. Car starts perfect, idles great, revs to 4K+ in park great...out onthe road from low rpm (1000-1500) in any gear if I stab it it will accelerate with sporadic hesitation. If I'm rolling along at say 50mph and 2500 or so rpm and punch it, it kicks down like it should and does pretty well with no hesitation. (stock TH350 with 92K on it)
The motor is a new GMPP 383 with about 1200 miles on it. Here's what I have done to date to try and resolve this:
New plugs (AC Delco)
new wires (2 different sets - Belden and Moroso)
new coil, module, cap, rotor
Timing is all in at 32* by 2800 rpm (32 recommended by GM for Vortec heads-tried 36* as well with no improvement)
Carb is freshly rebuilt Qjet (Lars)
new mech fuel pump
tank was just dropped and cleaned; sock cleaned; fuel lines purged and all flexible fuel hose replaced with new.
WTF am I missing?? Could a failing torque converter of tranny be giving me these symptoms?? I am at my wits end with this damn thing. Any ideas from you "seasoned veterans"??
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
What type of range does the engine operate at. I have been trying to do some research on torque converter stall speeds and it may be that your engine is not meant to operate at the low rpm speeds.
Then, when you get to higher rpm's it is fine. Likewise, when it is in park, the torque converter does not play a role. Here is the link that sperkins gave me. http://www.tciauto.com/tech_info/tor..._explained.htm
Just a thought.
Then, when you get to higher rpm's it is fine. Likewise, when it is in park, the torque converter does not play a role. Here is the link that sperkins gave me. http://www.tciauto.com/tech_info/tor..._explained.htm
Just a thought.
Last edited by dgruenke; Apr 6, 2006 at 09:39 PM.
Race Director
Joined: Feb 2006
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From: Inside the woods living my passion
St. Jude Donor '07-'08
Originally Posted by Perfomer
Are you getting a full 12 volts to the coil. May be low voltage under load .
Also did you convert a points ignitoin to a HEI style? If so points style has a resistor in one of the wires that you have to take out if you go to HEI style or else you wont get proper voltage to the coil..Just a thought.
Instructor
Joined: Aug 2005
Posts: 234
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From: Covington, Virginia
Hey NC, something to think about...saw this on a friend's 68 camaro a bunch of years ago, small block, 4 speed, holley carb, points dist was replaced by electronics (GM, not aftermarket), anyway, the car would do great at low throttle, slight pedal, when he would jump on it, it would spit sputter backfire, etc. He spent many months dealing with carb, etc...He called me one evening during the summer, had two buddies standing there with the hood up, I walked over we talked for a couple of minutes, He asked if I wanted to buy a camaro real cheap, I asked him how much, he said he would take a case of beer and a box of copenhagen. We were standing there looking, one of the guys revved the motor and it sputtered a little. I just happened to notice the distributor wire sparking against the firewall....... put some shrink tubing on it and away he went. I came by the next day with the beer and the tobak, he just laughed....Don't forget to look at the wires IN the distributor for scuff/lost insulation, if the spark advance plate has rubbed a raw spot on a wire?? loss of spark....
good luck..
gonzo
good luck..
gonzo
Thread Starter
Burning Brakes
Joined: Jul 2004
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From: Sick of these TOOLS & AZZHATS in DC
Originally Posted by dgruenke
What type of range does the engine operate at. I have been trying to do some research on torque converter stall speeds and it may be that your engine is not meant to operate at the low rpm speeds.
Then, when you get to higher rpm's it is fine. Likewise, when it is in park, the torque converter does not play a role. Here is the link that sperkins gave me. http://www.tciauto.com/tech_info/tor..._explained.htm
Just a thought.
Then, when you get to higher rpm's it is fine. Likewise, when it is in park, the torque converter does not play a role. Here is the link that sperkins gave me. http://www.tciauto.com/tech_info/tor..._explained.htm
Just a thought.
Thread Starter
Burning Brakes
Joined: Jul 2004
Posts: 1,235
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From: Sick of these TOOLS & AZZHATS in DC
Originally Posted by C3Racing
Also did you convert a points ignitoin to a HEI style? If so points style has a resistor in one of the wires that you have to take out if you go to HEI style or else you wont get proper voltage to the coil..Just a thought.
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Thread Starter
Burning Brakes
Joined: Jul 2004
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From: Sick of these TOOLS & AZZHATS in DC
Originally Posted by Bill Baird
Any backfiring (through the carb or popping through the exhaust)?
Do you have any black smoke coming from your exhaust when it's giving you trouble?
Do you have any black smoke coming from your exhaust when it's giving you trouble?
Thread Starter
Burning Brakes
Joined: Jul 2004
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From: Sick of these TOOLS & AZZHATS in DC
Originally Posted by sperkins
Big cam stroker motors are known for their low vacuum numbers. Have you put a guage on it to try and get a baseline?
this isn't a "big cam" stroker, it's a fairly mild roller.
Pro
Joined: Jan 2000
Posts: 741
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From: Indianapolis IN
Originally Posted by NC C3
No, not really. I run sidepipes with uncapped spiral baffles in them, so there is a little bit of constant popping because of that. But no backfiring thru the carb or the exhaust for that matter, and no black smoke either.
Hmmm. How did the plugs look when you replaced them?
Thread Starter
Burning Brakes
Joined: Jul 2004
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From: Sick of these TOOLS & AZZHATS in DC
Well, three of them were pretty black but not fouled.....the rest looked good. I am gonna pull 'em all again probably tonight and see what they look like. I am gonna upgrade to a 50,000 volt coil and a high output ignition module to see if that helps. As I stated above, I have my doubts about the Auto Zone coil and module that I have in there now.
Instructor
Joined: Aug 2005
Posts: 234
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From: Covington, Virginia
Is there ANY chance that you have had to replace auto trans fluid but see no spots where you park it?????
Are the fouled plugs on the pass side or drivers side??
gonzo
Are the fouled plugs on the pass side or drivers side??
gonzo
Last edited by mobjack68; Apr 7, 2006 at 03:37 PM.
Thread Starter
Burning Brakes
Joined: Jul 2004
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From: Sick of these TOOLS & AZZHATS in DC
Originally Posted by mobjack68
Is there ANY chance that you have had to replace auto trans fluid but see no spots where you park it?????
Are the fouled plugs on the pass side or drivers side??
gonzo
Are the fouled plugs on the pass side or drivers side??
gonzo
Yeah....I recently added about a half to 3/4 of a quart....no drips where it is normally parked. Honestly I don't really remember exactly which plugs were fouled.....but seems like they were on the pass. side.
Thread Starter
Burning Brakes
Joined: Jul 2004
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From: Sick of these TOOLS & AZZHATS in DC
yeah....I'm skeptical of EVERYTHING now man.....maybe it is a bad (new) plug or two.....if thats the case, I will be SO pissed! I am gonna pull all the ACDelcos tomorrow and try the Autolites. We'll see....
Pro
Joined: Jan 2000
Posts: 741
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From: Indianapolis IN
Originally Posted by NC C3
yeah....I'm skeptical of EVERYTHING now man.....maybe it is a bad (new) plug or two.....if thats the case, I will be SO pissed! I am gonna pull all the ACDelcos tomorrow and try the Autolites. We'll see....