Malachi151

I've seen several threads about this. Now I have a little more insight. This is a jerky type of hesitation that happens when going slow under 3,000 RPM when the car is hot. Its not the 3K hesitation under hard acceleration.

I noticed that this seemed to happen more at night, I thought because that was when I did more driving around, or the night air or something, but that is not it.

What triggers this to happen is having yoru lights on.

I have an A/F guage, and I notice that if I am driving along with the lights off and reading 2 bars of green, then I switch my lights on it will read 2 bars amber and 1 green, or whatver. Its always different, but the thing is, if I'm getting a steady reading of X, and I turn the lights on my reading immediately becomes more lean.

This happens when I turn just the parking lights on too. Its incrimental. If I have all lights off, then turn the parking lights on then I get a little more lean, then I turn the headlights on it gets even more lean.

So, when the car is hot and the lights are on it drives like total **** under light acceleratino or no acceleration under 3,000 RPM.

This started happening about 4 months ago. About a month and a half ago my car caught on fire. The fire started in the front relay box that is by the air box, and burned up my wiring harness. I finally got my car back fro being repaired (which was a total mess) and I still have this issue, in fact it may be a little worse.

Any ideas on how to fix this or what the problem may be?

BrianK

are you using the stock ECU? I'm having a similar problem. There is certainly something about the electrical system that is weird in this car. You'll also notice that if your running hot (but still well within the mazda temp gauge "middle" section) and you turn your parking lights on, your radiator fans will turn on - turn the lights off and the fan turns off too. It will still cycle on/off with or without the lights on, but having the lights on makes it happen sooner. Someone told me the same thing happens when you turn your A/C fan up to 3 (without the A/C on), but I haven't tried this yet. You might want to see if the A/C fan to 3 gives you the same reading in your A/F gauge

puma

iTrader: (2)

i believe it is a a/f ratio uage problem, not a ecu problem.

plug a volmeter on your o2 sensor and check if it still does the same thing.

personnaly, i have the hks type 1 turbo timer and i can monitor my voltage with it. When the voltage goes down, my a/f ratio goes down too.

i must say that i have an autometer though...

puma

alwan16

i had the same problem when i first got my car about 2 years ago....cruising very slow (no acceleration) the car would sometimes hiccup/jerk like there wasn't enough fuel or spark getting to the engine. it's gone away but i did check all the engine grounds and maybe add another one. just one more fd gremblin to not worry about once it's gone.

Malachi151

Hmm... the question is though, does your a/f guage change because of the voltage change or does the voltage change effect the fuel going to the engine?

I'm using autometer too BTW.

That fact remains though, that the car jerks around a lot at low speeds and low rpm, and it only does it when the lights are on.

It olny started happening recently, but then after all my repairs its still there and actually worse.

Suppose is a grounding problem, what exacly should I ground to what?

thanks

REDLINE

It almost definetly a grounding problem. I had the same problem, especially on cold moist nites. Car would be fine under hard acceleration above 3krpm, but anything below, it would start bucking like crazy!! The solution was to find a heavy cable and attach it from the engine block (theres a little loop attached to hoist motor out of bay) to the car's body using a bolt. Make sure you sand a tiny patch of paint away from engine bay for proper grounding. This solved the bucking problem.

Brian, as for the fans turning on, thats normal. When there is extra load on the alternator (lights, ac or fans switched to #3 or 4), this will cause the fans to turn on earlier than without any load. Thats why when I drive, I always turn the fan on to 3 or dirve with parking lights on.

luneytune

Glad you started this thread. I have seen very similar problems with my car. Where I noticed it first is every other day (not exactly) after the car is warmed up the idle is not smooth at 850 and the a/f is bouncing about 5 bars 3 amber and 2 green. If I put the car in first the idle immediately smooths out and the a/f display completely disappears, when I rev it to let out the clutch I get an initial hesitation then its ok. It is very repeatable. Like Malachi151 I get different things to my idle with different electrical loads on I know the ECU is aware of a lot of these, clutch switch, 1st gear switch, 2nd gear switch, lights fan setting and so on. But I also get the severe bucking sometime sub 3k. I am going to try a larger ground and see if it helps.

legendrx7

iTrader: (12)

Hey Man, we can try a new grounding strap on your car. I will probably have time Wednesday night if you want to do it then. I already have some large wire, we will just need to get a couple of terminals.

It will be easy to do and could be a super cheap and easy fix to your problem. Definitely worth a try.

give me a call or email and we'll take care of it Wed. night afterwork.

later,

Pumped

is your car jerking or is it just the tach?
my tach jerks around 1.5k to 3 k, but it does not affect the drivability, ...its just that you see the tach needle jerking around once in awhile. does any have this problem and how to cure it. thanks

lovemyseven

iTrader: (2)

I'm glad this is being discussed because my car is doing the same thing, and I just put a newly rebuilt motor in. I thought something was wrong with the motor, but it ran fine above 3000 rpm. Rob Golden at Pineapple Racing, who rebuilt my motor told me to check my grounds, and I do have one grounded to the frame of the car. He told me to make sure it is grounded to the engine, because it is a better ground. What does anyone else think about which is a better grounding area.

Blake

You must ground the block to get it to run right! It sounds like you forgot to hook up the main engine ground. Regardless, you should go through and check all the grounds, plus perhaps add a couple extras. All ground points should be clean and solid. Sandpaper is a great prep tool. I would also use a little "dielectric" (sp?) grease, which prevents corrosion at electrical connections. Use the factory service manual to find the stock ground points.

kelrx7r1

i thankyou guys for starting this post i am also having
problems under 3,000 rpms.i am checking my ground
tomorrow thanks again guys

duckyjp

I've got it too. Same symptoms. I haven't gotten around to adding a ground, mostly because I'm not sure exactly how to do it. This will be basically the first work i've done on the car myself. Does anyone have any pictures of the ground strap and how and where you attached it? Thanks. I took a look under there but I got a bit lost following the cable. I haven't had time to get a real good look with good light under there.

lovemyseven

iTrader: (2)

how do you add a ground?

Malachi151

Okay, I (Well legendrx7), fixed it.

We put in a new grounding wire. It was 8 gauge copper shielded wire, and sanded down the spot on the where the it would be attached. This was just a replacemt of the stock grounding strap that is up at the back of the engine and connectes to the body. The stock strap is unshielded.

We (he) also cleaned up my battery terminals and resecured them.

Evern since then I have no problems.

I also notice that my readings on my A/F gauge have changed back to what they looked like about 6 months ago. The readings are more clean, and more rich. I don't know if this is just the gauge, or if its an accurate reflection of what has been going on with the engine, but either wya its a definate qualifyable result from the work that was done.

legendrx7

iTrader: (12)

Yup! Anyone having problems like this should definately first clean and firmly reconnect their battery terminals. I feel this corrected Malachi151's promblem more than the new ground strip did. Tho it is hard to tell b/c I did it all at the same time. It all took roughly 10 minutes and the results were amazing.

rotary-tt

pulling off the battery cable always makes the car run better. Seems to reset the cpu (even without hitting the brake pedal). My car always runs better when I do this (but boost is down). The jerky stuff always comes back in a couple of days.

ROTORROCKET

I also have the jerky hesitation in low RPM's. The jerky hesitation is similar to trying to accelerate during an undershift ( shifting into a higher gear without sufficient RPMS). I have a grounding strap installed by Pettit Racing so I'm not sure if the grounding factor is to blame for this. I'm going to disconnect my battery terminals and clean the connections to see if that help any. I will post my results when completed.

1 BAD 7

i had the same problem (search for "bucking rx"), and after running a new ground wire from the negative battery post to the frame, it went away. it still shows up *rarely* when i have the headlights and a/c on, so i'm going to make sure i've got the new ground on bare metal, and check all other grounds, too. it's 1000% better though...it had gotten so bad i could barely drive it at night!