1500 rpm buck - EGR related?

[stangGT97]

(excuse the length) - ok, heres the problem at hand... a few months ago, I started to notice my car would buck at 1500 rpm (almost exactly), usually in gears 2-5 (cant feel it in 1st). It feels as though the power cuts out, then comes back and the car is almost shaking front to back. The bucking occurs at light throttle at the rpm specified, and immediately goes away when I give it more gas, feeling moderately smooth at WOT. The fuel filter has only about <10k on it, spark plugs are new autolite 764 coppers gapped to 0.054", wires are Motorcraft 8mm with ~15k on them and have dielectric grease swabbed in them to prevent moisture, coil packs are stock, driveshaft is torqued to spec, IAC is new, MAF has been cleaned, and sea foam was run through the intake a few times. If its relevant, transmission fluid has <10k on it, oil + filter are fresh, and the engine has never been sprayed with water. I'm running out of ideas! By the time I fix this problem the whole motor is going to be brand new lol.

So, I was reading that a malfunctioning EGR or pressure sensor can cause low rpm/part throttle bucking, but unfortunately I have not thrown any codes. As another symptom I am experiencing, sometimes my RPMs at idle will follow a sine wave and fluctuate from 850-550 and back and forth, and then hang other times. My buddy with a '98 ranger said that his truck was experiencing similar symptoms and replacing the EGR valve + pressure sensor fixed it, but he was throwing a code. Is it possible that my EGR system is fubared and needs to be replaced? I would say it could be a tuning problem (lean spot) but my car has never pinged and I run Shell 93 octane in it. Thanks all, I really appreciate any advice you may have.

 

[Gearbanger 101]

Sounds more like a bad TPS (Throttle Position Sensor) to me? They're about 40-bux

 

[jstreet0204]

Yes to both questions. EGR can cause part throttle bucking, and when mine was going out it did not throw any codes since it was sticking open, not closed. Try making a block off plate out of a soda can, and see if the problem goes away. It took care of mine until I eventually deleted it.

 

[stangGT97]

Yes to both questions. EGR can cause part throttle bucking, and when mine was going out it did not throw any codes since it was sticking open, not closed. Try making a block off plate out of a soda can, and see if the problem goes away. It took care of mine until I eventually deleted it.

hmm ok, i shall try that. I need to keep the EGR for emissions purposes (I think) cuz I live in MA and they're relatively strict. I will also check the TPS, my friend has a multimeter that I can use to check voltages.

 

[46gtsblown]

Instead of a block off plate for trouble shooting just remove and plug the vac line to the EGR valve.
If your symptoms clear up it could be the valve or what ever controls the valve operation.

Dwayne

 

[JohnyD05]

I don't believe its any of the sensors.

Is this when you get on and off of the gas? or is it when you are holding the gas at a constants level?

I don't think its any of the sensors, my car has done it since 33K and one of my friends has done it since low 20K. I attribute it to the driveline loading and unloading torque from the engine. Its kind of hard to explain. I know i get it if i get into the gas, and then come off the gas really quick at low rpm pretty much in gears 2-5, more so in the upper gears at low rpm and thus low speed. I don't think there is much you can do about it, you just learn how to use your foot and you shouldn't have a problem. If you do find that you can get rid of the trouble with a sensor, post it here cause i would love to fix it. But i think you are wasting your money.

I have the same symptoms, MY idle fluctuates, I talked to a ford Mechanic, and he said that 4.6's idle have sucked since they were introduced.

 

[JohnyD05]

hmm ok, i shall try that. I need to keep the EGR for emissions purposes (I think) cuz I live in MA and they're relatively strict. I will also check the TPS, my friend has a multimeter that I can use to check voltages.

Dan,
Does your car have ODB2? The new test, just involves a visual on the exhaust and plugging the computer into your ODB2 port, as long as you arn't throwing any codes, which can be turned off with a chip and and a tuner. Atleast this is what i am told and thats how my last inspection went.

I don't know how much you would gain by losing the EGR, I am kind of curious? also would u be interested in helping me do a cam swap this summer? and do you want some PI cams if i do?

 

[stangGT97]

Dan,
Does your car have ODB2? The new test, just involves a visual on the exhaust and plugging the computer into your ODB2 port, as long as you arn't throwing any codes, which can be turned off with a chip and and a tuner. Atleast this is what i am told and thats how my last inspection went.

I don't know how much you would gain by losing the EGR, I am kind of curious? also would u be interested in helping me do a cam swap this summer? and do you want some PI cams if i do?

yeah, I actually think they just plug the scanner into the computer port and theyre done. The bucking occurs at constant throttle while cruising along, so its not the driveline torquing up. Its really annoying and very pronounced at 1500 rpm.

Oh yeah, and I'll definitely help with the cam swap, but I dunno about buying the PI cams though. I'll probably be doing a full headswap with VT stage 2s and bassani midlengths (so I can keep my X) in the near future (hopefully)

 

[Dan_Soprano]

Try cleaning the MAF.

 

[JohnyD05]

yeah, I actually think they just plug the scanner into the computer port and theyre done. The bucking occurs at constant throttle while cruising along, so its not the driveline torquing up. Its really annoying and very pronounced at 1500 rpm.

Oh yeah, and I'll definitely help with the cam swap, but I dunno about buying the PI cams though. I'll probably be doing a full headswap with VT stage 2s and bassani midlengths (so I can keep my X) in the near future (hopefully)

You might want to look into stage 2's they make most of there HP at high rpm up untill 7K i think i have read, somewhere you don't want to be spinning your stock bottom end to. There was a post about a guy who put stage 2 cams in his PI heads and made less power then if he put stage 1's in. They need a very good intake and to be spun pretty high RPM. I wouldn't do the Stage 2 heads and cams unless you plan on going with a bullit or p51 intake and a built bottom end, and untill you do that i am not sure what kind of power you will see at the stock redline. for all that money a Blower might make more power for not much more money. that seems to be the boat i am in.

P.S. Mustangs wern't meant to be driven at 1500 RPM haha you should be at redline all the time ! Cleaning the MAF might be easiest with some carb cleaner ( basically free)