I tested my tps a few days ago.. it Overloaded right after 1/4 throttle. I was bucking like crazy after that. so i replaced it figuiring that this was the problem.. now i get the bucking from like 700 rpm - 3000 rpms. and it is fine after that .. well i figuired that i would try to adjust the idle cuz it was low. so i jumped the bac and the car ran really smooth.. i snapped the throttle real quick and no hesitation. the car was still warming up so i thought that would drive it up the street real quick to get it to operating temp. the car drove pretty good. considering i bought it about 1.5 months ago and it wasnt drivable.. it was my first time to be able to go through a decent range of rpms. anyway. i got it home and set the idle. shut off the car and got ready for work.. came back out started the car and backed up. got to the end of the road. and the bucking started again. I put the jumper back on.. it lasted long enough to get the car to turn around and back into my driveway.
Until that point I thought that i would clean or replace the BAC and i would be fine.. But now im not sure.
I was reading in the Haynes on some of the things to check or replace so far i have done

New air filter
New Exhaust from Manifold back
New Plugs
New Wires
Oil and filter
New Tps
Fuel Pump
Fuel Filter


that pretty much eliminated like 50 percent of the trouble shooting page for my problem

Could it still be the BAC
or the Egr??
Im going to check Fuel pressure. and test the FPR
Other than that im stumped
Also one other thing
I read once that you shouldnt replace the thermostat with a aftermarket or the car could run bad. well when i was double checking everything again i felt the top radiator hose and it was almost solid. i mean it has a little give but not much.. didnt really feel right . could that be the thermostat being stuck?? Although i dont run hot or over heat. also on that note. I was tightening the air pump belt and i used a pry bar to put a small bit of tension on the air pump and the housing for the thermostat leaked a small bit of of fluid. but its doesnt leak normally. I was just wondering if this could be a problem as well

sorry for the long story .. im just tired of hitting dead ends and im hoping someone can help me

 

mazdaspeed7 explained the bucking of FCs as a tuning problem. he eliminated it with a standalone. he explained it and i knew exactly what he was talking about. its in lower gears, such as driving around parking lots.
oh, and by the way, i didnt read your post. i just read bucking...

 

but it doesnt buck and go up in rpms.,. it bucks , cuts out , stalls. that type of thing.. like it falls flat on its face

 

Run a shitload of injector cleaner through it.

 

stock motor or ported ? if ported, that _might_ be a problem (on stock ecu).
otherwise, good luck.
when mine bucked, the rpm didnt jump up, per se, just bounced (kinda up and down).

 

Bucking is generally one of 5 things:

no pill in the pressure sensor line (or bad pressure sensor)
poor ecu grounds
bad filters/fuel pump
clogged injectors (run injector cleaner!)
TPS

 

stock motor,, 77 gs on it .. ill try the grounds and the injector cleaner tommorow.. and ill test the fuel pressure.. any other things i should try ??

 

update.. I put in the injector cleaner.. car runs a little smoother.. i did a fuel pressure test. the t2 fuel pump was pulling about 25 psi at the inlet to the fuel rail and about 30 at the rear of the line.. the pressure hold test was close to the 18 psi that was stated in the haynes manual. figuiring that the pump was bad i put in a new walpro. now im getting a litte of 40 psi .. which is closer to the spec.. but i just tested again.. when i start the car and let it idle for a minute the psi stays at 40 when i hit the gas the gas cuts out and the psi drops to 30.. what is causing this .. i think this is my problem .. is there a sending unit that controls the voltage sent to the pump???

 

Another Update.. at idle the car is drawing 7.45 volts on the blue and white wire that hailers mentioned in another thread about FP voltage. at 6rpms.. ( was shocked the car made it up that far). it pulled 8.30 volts .. that doesnt sound right at all .. can someone veryfy this.. also right from the pump to the FP gauge i was pulling about 29 psi .. This is grounds for a rewire?

 

You need to rewire your fuel pump. It sounds like your wiring is faulty.

 

Maybe I'd better post my pitch about grounds:

The ECU uses low voltage signals from sensors (like the TPS, the boost sensor, & the O2 sensor).
Most of these sensors have their own ground wires, but if the primary grounds are the least bit weak, the ECU grounds try to carry the noisy spark and alternator loads also. The ECU tries to compensate & goes nuts.
The cheesy firewall to bell housing ground just clips on. Replacing it with a heavy gage wire with eyelets & bolts is a good start.
I have also seen improvements by adding a ground from the spark coil mount to the alternator frame.

 

well i checked the ground for the fuel pump relay.. under the air box.. well now i carry a idle voltage of 7.89 and it will go up to about 11.38 volts.. but its not constant and flucuets. I resanded the ground 2 times. and this was the result.. i guess ill still need to rewire. ill have to do that tomorrow i think

 

our cars must think alike 'cause mine is doing the same thing.

 

yeah dude.. well im going to have a lil more time tomorrow to wire this baby up . hopefully it solves all my problems.. im tired of guessing . heheh

 

what...? is there supposed to be a check valve in the pressure sensor line?? I replaced that with a vac line... This why I keep getting the Pressure Sensor CEL?

 

It's not a check valve. It's a restrictor pill that prevents sudden changes in readings. It should be about 1/2-1" in from the end that plugs in on the engine.

 

I think I've got an idea what you're talking about. Its not by chance green is it? I'll have to rummage through the old vac lines. Could this cause the pressur sensor issue?

 

I don't believe it'd throw a code, but who knows. I've only ran once without it.

 

Pull those injectors and have them professionally cleaned. Sounds like your primaries are clogged, and when the secondaries come online at 3800 RPM its gets the fuel it needs. Injector cleaner can only do so much.

-Joe

 

I'd say at this point, it's the fact that his fuel pump is only seeing 8 volts. I wouldn't even worry about cleaning the injectors right now, chances are once the fuel pump is fixed, with the injector cleaner you'll be good as new. If not, then go with the above suggestion. But the fuel pump is *definatly* the more serious of the problems.

 

Hey SonicRat...is there a specific brand of injector cleaner you recommend?

-Joe

 

I've had the best luck with chevron techron. I run about two bottles to 5 gallons (yeah, I know, it suggets running 1 bottle to a full tank, but I don't like that way!) and pretty much that has always done the trick for me if it was anything with the injectors.

 

ok i have another update.. i did the rewire drove it around .. ok ,, she drives BUT i have no real throttle.. i ll punch it and the car hesitates , no matter what rpms.. i can feather it and it drives.. but i have no real power. so far i have
new air filter
new fuel filter
injector cleaner
re wired fuel pump
new fuel pump
new tps
new plugs
new wires
and nothing yes im getting there slowly. but how can i get this thing running right ??

could it still be the injectors?? fpr?? im not sure what to try anymore

 

So you've now got 14volts to the FP right? Well that's definatly one less thing. Have you added extra ground wires yet?

 

You think this method would clean them almost as well as a professional shop cleaning? Mine seem to be fine, but I'm due for a cleaning and I'm wondering if I should just run the cleaner additive.

-Joe