i have a 86 N/A and im having this same problem ..

 

Thinking back...the car ran much better when the boost sensor was disconnected. I have my boost sensor ran to the nipple in the UIM, but I've run all the rest of my gauges, bov, and such to different nipples on the TB...I've heard some of those nipples are used for different things but I didn't look through my manual to see which ones, could that be causing a problem?

 

Does anybody know about the stock vacuum line restrictor pill between the manifold and the MAP sensor? I just read about it in another thread and how it can cause the ecu to cut/dump fuel if the 'pill' is not in the vacuum line...just a thought

 

I have a pill in my line. I took my '7 to a neighboring city yesterday though and I don't think it started doing this even once. I had one hiccup where it barely stuttered and went to 18.x AFR, but I was running CRAZY low on gas. When I finally got to the gas station I put in 14.517 gallons...

 

I'm going to look into this 'pill' idea for this weekend. Is this something I can find in my Hayne's manual? Or could you post a pic of what/where it is cuz I've never heard of a 'pill' in a vacuum line

 

ORIFICE. See the parts fische online.

 

Ant- The FD uses "pills" in the wastegate and pre-turbo control lines. Replacements can be had from Mazda for cheap. Holley jets can also be used. As a rough test, you can get a clamp and pinch the hose( restrict it as the pill would) and see if your issue goes away when the hose is restricted. just don't pinch the hose shut all the way.

 

Here's a couple of jpg out of the parts fische.

 

Interesting...so which vacuum line exactly should I be putting this orifice on? The one to the boost sensor?

 

Ok, this is starting to make sense. My guess as to what is happening is once the car warms up it goes into open loop where it starts taking input from all the sensors on the car, therefore, if the boost sensor is sending erroneous information from not having the orifice, the car isn't going to function properly.

But when the car is cold "and runs fine" it drives in closed loop where it already has preset fuel mixtures built into the ECU just to keep the car safe and driveable until it warms up.

Am I on the right track with this mindset?.....Man I should be studying for my test that's in an hour and not this, lol....what can ya do

 

i dont think its a problem with the pill. having the pill in there definately helps with making the signal from your pressure sensor steady, but i dont think its causing your problem.

I had your same problem when i was running rtek2.1.. i found out it only happens if you take any too much fuel out in vacuum. but it didnt seem gradual, like i could take out a little and it would run fine, but just a hair more fuel taken out and it would lean way out to 18's

 

Post removed by Hailers.

 

Probably not the orifice (talking to the original poster only). But I'd install one anyway. Its for dampening the vacuum signal to the boost sensor during sudden acceleration as to not muck up the signal.

Rock hard grommets on the injectors bottom side can cause air leaks but are easily found spraying starter fluid at idle in the general area of the injectors.

Does your boost sensors vacuum line have vacuum on it at IDLE?

Spray starter fluid around the back of the throttle body at idle to make sure the three/four nipples back there are not leaking.

Try driving the same but with the 02 disconnected at the 02 sensor and see if the afr's/hesitation is different or not.

Stock injectors? Do you have some device controlling fuel? Like a SAFC or????

 

Sure sounds like the closed loop operation is not working right; AFR at cruise and light accel should be near stoichiometric (14.7:1), assuming your aftermarket ECU is managing that region the same as the stock... since you have an O2 sensor, that would imply it is (or is supposed to).

I would check to see that the ECU is really going into closed loop at cruise... and what is the O2 voltage there? It should toggle back and forth between about .6-.8 (rich) and .2-4 (lean). It could be that your ECU is getting a (false) rich signal, and is reducing the mixture to try to get to stoichiometric, causing the lean condition. That would be consistent with your AFR readings (ok in open loop, lean in closed).

 

Just ordered one from Mazda...$3.90 including shipping, can't hurt to go ahead and put it in there



This was my initial guess, I'll be checking them on Saturday, if they're leaking should I order new ones from the factory or would a local parts store be fine?

I believe so, it's plugged into the single nipple coming out of the UIM that points toward the strut tower.
Nope, standard rtek 1.7 with 720cc secondaries...

 

This sure sounds like the ECU is not playing properly with the O2 sensor. AFR at cruise should be around stoichiometric (14.7:1), and the O2 reading should be toggling between high (>0.5v) and low (<0.5v). Assuming your ECU works in closed loop like the stock unit, if it is getting a steady false high (>0.5v) at cruise, it will ratchet down the mixture trying to correct that and give you the lean AFR you are seeing, and result in lean misfire. Under more throttle, the stock ECU goes into open loop (I assume your programming does the same), which would explain why it runs well under heavy acceleration.

Not the only possible cause, but worth checking. See what the O2 voltage is doing during steady cruise... if it is not toggling, that will narrow down the possibilities.

 

so the Mazda dealership lost the orifice when I went to pick it up this morning....sigh, now I have to wait until Monday :/. I'm thinking about either disconnecting the vacuum line or tieing a ziptie around it so I can at least drive it around tonight and throughout the 60 degree weather weekend?

 

It might be that when the boost/pressure sensor is disconnected..........the car won't go into closed loop. In fact it won't. That's a given

So. Instead of pulling the plug on the boost/pressure sensor, PULL THE PLUG OFF THE 02 SENSOR instead. Little to NO harm in doing that. THEN see how it drives.

 

aha! great idea! I'll do just that this afternoon

 

disconnected the 02 sensor and ziptied the vacuum line to the boost sensor. Problem is still there slightly under light load which leaves me to believe that it could be a clogged up fuel filter from all the premix I run...replacing that in the morning

 

nope, longer I drive it the worse it gets, was trying to cruise around with some friends but AFR's stayed in the 18's and the car was bucking so I had to turn around and miss all the fun . Will be trying more ideas tomorrow...

Things noted...open/closed loop make no difference in performance....mechanical problem then? possible clogged fuel filter or sock in fuel tank? Voltage drop to fuel pump? Hopefully find out tomorrow

 

Does not seem to be a clogged filter/screen to me since the hesitation goes away when the pedal is depressed. Only happens under light throttle from what I remember.

MIGHT be a AFM problem. But only if someone has removed the large black plastic cover off it and moved the spring tension to where it should not be.

Does the pressure/boost sensor have the right part numbers on it. NOt a non turbo sensor in a turbo car or vice versa. Same with the ECU part numbers.

 

it's a N318 boost pressure sensor, whether this the right one or not I'm not 100% sure because when I replaced my AFM I found out it was a s4 n/a I believe. I know that the connections to the AFM aren't as tight as they used to be, it's possible that may be affecting it too...

On a side note...went to the local 1/4 mile strip at Charlotte today and witnessed a 450whp FD hold off a 725 whp supra until about the last 100ft!

 

....stumped again...

Me and a friend tried swapping our n318 boost sensors..., running the car without the tps and air temp sensor connected (by mistake), capping a minor vacuum leak from my water injection, reconecting the 02 sensor to no avail...I'm stumped at the moment and a little frustrated with this thing cuz damn it pulls hard under boost which is a lot of fun until I look at my AFR gauge and it's reading 13's and up .

...motor still lives to see another day, but gotta get this fixed before my right foot gets tired of restricting this thing

 

disconnected my n318 boost sensor...problem vanished and car runs better than my DD saturn sc2. I can cruise from 1k-2k rpms all day long any gear without a blip and AFR's won't go over 14.3. It isn't adding much fuel under boost which I can understand without the boost sensor being there so I'm keeping a light foot but boy is it fun just to be able to drive without having to fight the car in every gear...*sigh of relief*...

Any ideas why this is the case fc Guru's?