Car shakes/jerks when getting back in the gas

[zer0c123]

My 93 240sx Manual fails smog 2 times, then i have it fixed at a goldshield station. After the repairs, it passes with numbers that were way lower than before. Basically the diagnosis was, "weak vaccum to EGR valve due to clogged EGR passage to BPT valve." Here is the thread if you wanna read up on the smog problem zerothread?id=118420

Ever since i got my car back from the shop, i get this weird jerk or shake at low rpms. For example I'm accelerating in 2nd gear, then just take my foot of the gas, and let the rpms drop down to 2000. If i get back on the gas the car jerks/ shakes until i go past about 2.5k-3k rpms, it feels like the car wants to jump or something. If i get back on the gas lightly, the jerking feeling isn't as strong buts it's still there. But if i floor it, theres no weird jerking feeling.

My first gues. was probably the shop adjusted my timing, but the invoice for repairs don't state timing adjustment. Just egr valve cleaning and smog inspection. The car idles at 700rpm, which is about the same when i had the timing adjustedt to 20 BTDC.

When i find time i might drop by the shop again and have them look at it. I think this may be still covered under labor warranty. I'm hoping this is something easy to fix, already spent enough money.

Edit. I noticed this weird jerk because i tend to drive at a constant speed, because of slight traffic where i live. Since there's traffic i let off the gas alot, then get back on it. ( like an automatic i guess)

Modified by zer0c123 at 10:05 PM 6/9/2005
Modified by zer0c123 at 10:07 PM 6/9/2005

[NISTECH]

It is due to egr operating to soon now, My guess is, and this happens pretty frequently, when the shop cleaned your EGR passage they drilled out the end of the BPT tube that had a restrictor in it. The very end of the tube had a reduction in the diameter of the hose to reduce the amount of initial back pressure supplied to the EGR. To perform a quick test simply pul the Vaccum line off the EGR and srive the car to see if the hesitation is gone.

[zer0c123]

I stopped by the smog shop on my way home today and asked them about the problem. Their explaination was that it was the egr flowing more freely now since it is no longer clogged. They said they could put a restrictor on the egr since i already passed smog.

After reading your reply, i'll give that test a try.

Thanks

[NISTECH]

You can put something in the BPT hose to perform the same task the restrictor does. They used to use it in vaccum lines on older cars. Its a little metal thing with a small hole through it to reduce flow to certain components, They are usually where there is a clored band around the vaccum hose. I dont know anyone that sells this seperatly. So a wrecker is your frend on this, most manufactures use this technique to control vaccum supply. Just cut the hose open where the band is and pull out the metel "slug" and shove it in your BPT hose Be sure the hole allows flow though.

[zer0c123]

I pulled one of the vacuum tubes from the BPT valve today and drove all the way to work with it. The ride was smooth with no jerks or hesitation, the ride was like it was before the smog repairs. Then after putting the tube back on, the ride was rough again. I probably can't leave the tube just pulled out like that forever so i'll head to the junk yard and try find what you were talking about.

I remember my local junk yard has alot of late 80's to early 90's hondas and toyotas. Hopefully they'll have what i'm looking for.

[NISTECH]

even american cars use that restrictor, so basically what ever is closest to the front of the yard just start pokin your head under the hoods of those cars. All the wreckers here seem to put the nissans in the farthest back corner of the lot..lol

[zer0c123]

I couldn't find that metal thing you were talking about. I looked at a bunch of cars feeling around the vacuum hoses, but i couldn't find anything that would fit inside my BPT hose. I did find this small plastic cylindrical looking tube with 2 skinny vacuum hoses connected to the top and bottom ( imagine a tiny soda can with staws sticking out both ends). It was in an old honda civic i think.

i ended up going back to the smog shop. THe tech took a small tube that was probably about 1/2 inch long and inserted a smaller metal tube inside like a straw. I think he took one of the 2 hoses from the top of the BPT valve, cut it in half and then reattached it to the small tube. He said if that didn't work, he would add another one of those tubes probably to the other hose.

I didn't get to really test the car out, I just wanted to get home as i fast as possible for the NBA finals

The smog tech said that he didn't drill the BPT tube, just cleaned it. He was saying this doesn't make any sense. My car should have been running better and should be getting better gas mileage ( I told him that my gas mileage has been horrible since passing smog). My street driving distance is about the same. For highway, i just don't have to drive as far out of the city this summer.
Modified by zer0c123 at 7:21 AM 6/15/2005

[zer0c123]

Even though the car runs better now, I was taking a closer look at the egr system and noticed something on the BPT. That material in the middle of the BPT looks like a chunk of it is missing. From what i could see one whole side is chopped off, maybe about 1/4 of the material is missing. Could this be a problem?

[NISTECH]

nah thats just a filter to prevent crap from being sucked in. it wont have any effect on how the car runs unless it does suck something in there.

[RaceBoy69]

why dont you take the egr off. you will find the plate to cover the opening at ebay..for $10 and change

[zer0c123]

I thought about taking the egr off or just plugging it up, but then I will probably need to reinstall it i when smog comes around again. Also i've read some mixed opinions from reading a bunch of posts.

I think i found the problem. I took out the whole EGR BPT valve, and saw that the BPT hose that i replaced was gone. In its place was some generic vacuum hose and the hose was even shorter than the real BPT hose. The hose is so short that when it bends, almost no air can pass through. I don't know why those mechanics put that hose there. I guess they dropped the real hose in the engine bay some where, because i did that too when i was replacing it. Took me a whole morning just find it.