Boozer007

I have a 93 R1 that I recently acquired, and it's exhibiting a strange behavior. When first running the car, during acceleration, it bucks fairly hard, especially in first and second gear. It acts like it wants to stall, but ultimately doesn't. After a few miles of driving, the issue seems to clear, only to re-appear the next day when I first start it up and run it. It idles great.

Before I got the car, it sat for a couple of years. When I first got it a couple of months back, I flushed the fuel and oil, and had the OMP replaced (it was throwing a code and going into limp mode). No codes now and it starts and runs great, especially after I've driven it a few miles.

I changed the O2 sensor and am still having the issue. Now, I'm leaning towards replacing the plugs, fuel pump, and or fuel filter.

Has anyone else had this issue or have any idea as to the cause? Would a fuel pressure issue clear up after about 5 minutes of driving?

Thanks in advance.

Boozer007

To be clear, it kicks hard for about 3 or 4 seconds and then takes off as if nothing is wrong. If I slow back down and then accelerate again, it'll buck again for a few seconds and then move on.

DaleClark

iTrader: (55)

Stock ECU or PowerFC? Is the car modified?

Dale

Boozer007

DaleClark

iTrader: (55)

Is it primarily around 3000 RPM? Pretty much all FD's buck around 3k with the stock ECU.

You can add an additional ground from the battery negative terminal to the chassis and it helps with the 3k hesitation but it doesn't totally go away.

Dale

Boozer007

It is primarily around 3000RPM. It feels like it's going into limp mode and then quickly reverses course. Back and forth about 3 cycles like a bucking Bronco and then takes off. It bucks enough to chirp the tires.

It just seems odd to me that it goes away after about 10 minutes of driving, and then returns the next day (or the next time it's been driven after a delay). I have an automatic 93 Touring as well that I've had since 1999, and have never experienced this with that car.

I'll run the extra ground like you suggested and report back. I may try to get some video posted to YouTube as well.

Thanks again.

DaleClark

iTrader: (55)

Could also be due for a tune-up - new plugs and wires, check the coil packs, new fuel filter.

Dale

Boozer007

New plugs are supposed to arrive today. Fuel filter was on the list just because of it sitting for so long. May tackle those this weekend.

Will update the thread when more is done/known.

Thanks!

Boozer007

Here's a video of the before and after. The image stabilization of my iPhone really smoothes it over. It's a lot worse than it looks, but you do get the picture in the first part of this clip. The second half shows a smooth acceleration after about 5 minutes of driving.

monstermills

iTrader: (2)

Mine does the same thing if its cold, its a 93 touring from Cali. I have all the stock engine components, I don't go above 3k until I'm basically 5 or 7 mins into a drive, from what I read it is a combination of things. I have added a ground to the driver side wheel well as Dale pointed out, I think that has helped it a little.

Clinton

Boozer007

Interesting. I also have a 93 Touring and don't have this issue.

Not knowing the fully history on this car, I'm going to replace plugs, fuel pump, fuel filter, plug wires, and coils packs. Hopefully one of those will solve it. If not, it's on to a new ECU (which I want to eventually do anyway).

Thanks guys!

nopistons1994

iTrader: (1)

I have a 93 touring Cali car (just bought it last month) and on the stock ecu I didn't have this issue. 3k hesitation? Sure, but physical bucking no.

DaleClark

iTrader: (55)

Every FD is a little different, I've driven cars where the 3k hesitation felt like a little dip in power and that's in, and I've driven cars when cold that would throw you through the windshield at 3k.

I know there are a lot of RX-7 folks in your neck of the woods, you may want to find someone who has a PowerFC that you can borrow. The PowerFC totally fixes the 3k hesitation.

I would go ahead with the tune up. If it's still there, try a PowerFC and see if it goes away, if so you know that's the problem.

Also, make sure your air pump is running. The air pump is electrical and the clutch engages and disengages by the ECU. If the wiring to the air pump shorts out (which is common) it will pop the fuse and the car will idle rougher, be jerky on/off throttle, and just drive weird. Probably not the problem, but worth spending 5 seconds to see if the air pump is engaging and running.

Dale

Boozer007

I don't know anyone in my area with an FD. Not sure how/where to check.

I've replaced the fuel filter, spark plugs, and spark plug wires, and run an extra ground from the battery's negative terminal to the chassis with no change. Still bucks hard when cold.

Other items on the list are the fuel pump and coils. Any suggestion on which one to tackle next?

Someone local suggested that it could be the MAP sensor. That thing is bloody expensive ($475 at Advance), so I think I want to make SURE it's that before pulling it and replacing it.

DaleClark

iTrader: (55)

May want to post in the SE RX-7 forum. I'll PM someone that I know that lives in that area. There's a LOT of RX-7 folk in TN, I see them every year at DGRR.

I seriously doubt it's the MAP sensor, they are extremely hardy and if they fail they full on fail where you are getting nothing from it.

Dale

Boozer007

monstermills

iTrader: (2)

Murilli

iTrader: (1)

I had really bad bucking issues, so i added a ton of grounds (while on the stock ECU), this seemed to solve the issue, until about a month later it came back full force. It was so bad, my girlfriend wouldn't want to ride along in the car. Hot, cold, low throttle, WOT it didn't matter. I went PFC, and no more bucking. I swear though, it would happen at 1500, 2100, 2500 and 3000, it was unbearable driving. It was fine over 3k though.

Definitely felt like being thrown through the windshield, accurate description. PFC should fix it for you.

djseven

iTrader: (56)

Im just North of Nashville in Hendersonville and will be glad to help. I have owned a lot of FDs over the last 16 years and can likely help you get it resolved. I'd be happy to look over the car as well and point you in the right direction.

David
615-756-8008

skyactivr

I'm a newbie but every little helps huh?
When I got mine it was doing the same thing but when warm - meaning I was able to get it over 3k and not worry - and once it was above 3k the problem totally disappeared. I could then turn the car off at a fuel station, fuel up and drive again and the problem would not be there for about two minutes, then it'd be back in full force.

Turned out my problem was thw ground strap that attaches in the middle of the spark plugs simply wasn't there. Got some thick wire and bolted it from there to a bolt on the body under the battery and the problem disappeared. Spent £3.

Boozer007

As they say, "You always find it in the last place you look."

After adding an additional ground wire to the battery, replacing spark plugs, plugs wires, O2 sensor, and fuel filter with no luck, today I finally got around to replacing the fuel pump. When I took the existing one out, I noticed it was not stock. Cheap aftermarket. Ah Ha!! I replaced it with a second-hand OEM Denso pump and PERFECT! Smooth as silk. Zero hesitation, zero bucking.

Folks. Please don't put that cheap crap in your cars..if not for your sake, then for the sake of the next guy who gets it.

Thanks to everyone who chimed in for the advice. I'm glad to get all of the other parts swapped out as well. Now on to installing the Apexi!

DaleClark

iTrader: (55)

Nice! Thanks for updating us!

Sometimes it's a chore to track down sloppy work by a previous owner. I agree, do it right!

Dale