Missing?

89GT5.0GIRL · 08-05-2001, 09:50 PM

I have an 89 GT with performer RPM upper and lower intake, full exhaust with cats, and 4.10 gears in the rear. When I have been driving my car jerks. I thought that I could just need new spark plugs and thought that it was just missing. I also thought that it did this because of the gears but am not sure. I just bought this car a month ago and just am wondering what it could be. Any suggestions would be great. Thanks.

jwboner · 08-06-2001, 02:33 AM

What rpm and mph is it missing/jerking? Not sure if would be spark plugs, sounds more like the gears to me. They will jerk at low speeds.

------------------
65 fastback
347 DFI injected, TFS heads, T5, 4.11 9", tc subframe conns, torq thrust D's
A little history lesson using today's tech.

89GT5.0GIRL · 08-06-2001, 05:56 PM

It jerks all the time in every gear. Not sure on RPM though. Also when I'm not pressing on the gas and am just cruising it doesn't do it. When I give it a little bit of gas it does it and when I give it a lot of gas it doesn't but as soon as I let off the gas a little it does it again. Hope that helps out a little.

jwboner · 08-07-2001, 12:37 AM

Well, based on that I would say it might be some sort of slack in the driveline somewhere or a fuel delivery problem. Does it make any weird noises (other than the actual jerking) from the motor while doing this? My car surges b/c of the carb and big cam when I go too slow and the motor wants to go. I'm sure there is an easily over looked answer to this, just have to find it.

moosejaw · 08-07-2001, 01:01 AM

This sounds like mass air meter interference. If you have an exposed air filter in the engine compartment this would be the cause. The air pressure waves (aka fan wash)from the fan will disrupt the air meter.

The air meter, being the largest part of the computers fuel equation, determines how much fuel is required (indirectly) and when its signal is disrupted it will subsequently "lean out" or "go rich". Hence the bucking is caused by the "lean" condition. This happens so fast it appears to be a miss but it is not.

Simply place a piece of cardboard or similar device along side the air filter to block the air flow path from the fan to the filter. This is a high tech problem with a low tech solution.

Mike

------------------
Live near St.Louis?
Check out Mustang Muscle and Dyno in High Ridge, MO
Check out my ride.

89GT5.0GIRL · 08-07-2001, 09:27 PM

Thanks for all your help guys. I had my dad look under the hood today and we saw a spark plug wire laying right on the headers. I got new wires and plugs but if that does not take care of the problem I will deffinately try your advice about the carboard. My boyfriend was sitting with me when I was reading him your solutions and he said, "Wow I never thought of that." That's true. I'm also glad that it is a cheap solution too. Thanks again guys for all your help and I'll let you know what happens.

89GT5.0GIRL · 08-10-2001, 10:26 AM

Hey found out I needed new plugs. Runs fine now. Thanks for all the help.

08-05-2001, 09:50 PM	#1
89GT5.0GIRL Registered Member Join Date: Aug 2001 Location: Dale City, VA, USA Posts: 8	Missing? I have an 89 GT with performer RPM upper and lower intake, full exhaust with cats, and 4.10 gears in the rear. When I have been driving my car jerks. I thought that I could just need new spark plugs and thought that it was just missing. I also thought that it did this because of the gears but am not sure. I just bought this car a month ago and just am wondering what it could be. Any suggestions would be great. Thanks.

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08-06-2001, 02:33 AM	#2
jwboner Registered Member Join Date: Jun 2001 Location: Under the hood Posts: 164	What rpm and mph is it missing/jerking? Not sure if would be spark plugs, sounds more like the gears to me. They will jerk at low speeds. ------------------ 65 fastback 347 DFI injected, TFS heads, T5, 4.11 9", tc subframe conns, torq thrust D's A little history lesson using today's tech.

08-06-2001, 05:56 PM	#3
89GT5.0GIRL Registered Member Join Date: Aug 2001 Location: Dale City, VA, USA Posts: 8	It jerks all the time in every gear. Not sure on RPM though. Also when I'm not pressing on the gas and am just cruising it doesn't do it. When I give it a little bit of gas it does it and when I give it a lot of gas it doesn't but as soon as I let off the gas a little it does it again. Hope that helps out a little.

08-07-2001, 12:37 AM	#4
jwboner Registered Member Join Date: Jun 2001 Location: Under the hood Posts: 164	Well, based on that I would say it might be some sort of slack in the driveline somewhere or a fuel delivery problem. Does it make any weird noises (other than the actual jerking) from the motor while doing this? My car surges b/c of the carb and big cam when I go too slow and the motor wants to go. I'm sure there is an easily over looked answer to this, just have to find it.

08-07-2001, 01:01 AM	#5
moosejaw Registered Member Join Date: Apr 1999 Location: St.Louis,MO Posts: 274	This sounds like mass air meter interference. If you have an exposed air filter in the engine compartment this would be the cause. The air pressure waves (aka fan wash)from the fan will disrupt the air meter. The air meter, being the largest part of the computers fuel equation, determines how much fuel is required (indirectly) and when its signal is disrupted it will subsequently "lean out" or "go rich". Hence the bucking is caused by the "lean" condition. This happens so fast it appears to be a miss but it is not. Simply place a piece of cardboard or similar device along side the air filter to block the air flow path from the fan to the filter. This is a high tech problem with a low tech solution. Mike ------------------ Live near St.Louis? Check out Mustang Muscle and Dyno in High Ridge, MO Check out my ride.

08-07-2001, 09:27 PM	#6
89GT5.0GIRL Registered Member Join Date: Aug 2001 Location: Dale City, VA, USA Posts: 8	Thanks for all your help guys. I had my dad look under the hood today and we saw a spark plug wire laying right on the headers. I got new wires and plugs but if that does not take care of the problem I will deffinately try your advice about the carboard. My boyfriend was sitting with me when I was reading him your solutions and he said, "Wow I never thought of that." That's true. I'm also glad that it is a cheap solution too. Thanks again guys for all your help and I'll let you know what happens.

08-10-2001, 10:26 AM	#7
89GT5.0GIRL Registered Member Join Date: Aug 2001 Location: Dale City, VA, USA Posts: 8	Hey found out I needed new plugs. Runs fine now. Thanks for all the help.