OK so i have had this problem for some time now, i have spent hundreds of dollars on parts, labor, etc. trying to figure out what the hell is wrong with my car. i have been told it was my MAF, fixed that, then plugged secondary injectors, fixed that or cleaned that actually, there were sediments in my gas tank, fixed that, dirty fuel filter, fixed that, intake clogged with carbon, fixed that. my fuel pump IS working fine, fuel pressure is normal. so what the hell could it be???? and now my most recent discovery was possibly my pressure sensor is bad. but anyways, i drive an 86 GXL, it is in VERY good shape. i really don't feel like explaining whats wrong with it again since i have posted numerous threads explaining exactly what my car is doing, so i made a video and posted it on youtube. PLEASE watch my video and tell me what you think it might be. THANK YOU THANK YOU THANK YOU all in advance!


heres the link: http://www.youtube.com/watch?v=zL6duJReGas

 

It almost seems like a very bad 3800 rpm hesitation. The common fix for the hesitation on an '86 is regrounding the pressure sensor. I think there was even a Mazda technical service bulletin for it at one point? The FSM shows the wire color as Black/White, and it also happens to ground just about ever other sensor on the car, as well. So if you splice into it and add a connection to a clean ground point like the shock tower, you would be cleaning up the signal from many of the sensors to the ECU. It's defintely worth a shot.

 

On a normal 86 car, the secondary injectors can't come online at all unless you do some off rigging. So......studdering in the driveway shouldn't be the secondary injectors.

ON a 86 non turbo you can rig it so the secondarys come online in the driveway by unplugging the hose to the pressure/boost sensor (cap the vac line) . Then each time you rev to 3800 rpm the secondarys will come online in the driveway.....and it'll sound crappy when you hit 3800rpm. This procedure is shown on page 4A-69 of the 86/87 FSM. Sorry, not online anywhere I know of.

I only mention this because you say you have the same problem in the driveway. The lack of vacuum to the boost sensor would make the secondarys come online anytime 3800 was reached (not a normal thing). The lack of a vacuum on the boost sensor simulates LOAD and LOAD plus 3800 rpm equals the secondarys coming online. Secondarys should only come online at 3800 rpm under LOAD and while driving,.

So idle your engine. Pull the vacuum line off the boost sensor. Feel the vac line to see if it has vacuum on it ......or not.

Also see if you boost sensor line has a small orifice inside the line at one end or the other. Should be at the end of the line at the intake. It should be up the line a inch or so. It's called an ORIFICE. Spend the extra three bucks for one from the Mazda dealer. Part number can be found by searching this forum using HAILERS and ORIFICE as the words. It's part number is out there somewhere. I left his item out of my 86 once upon a time and it cause a bad hesitation problem just about any speed if I put the pedal down. This fix does not work for everyone. I know not why. The orifice probably won't be the problem if the hesitation happens at just 3800 rpms.

Boost sensor...............that's what MAZDA calles it in the FSM, even though your car is not turbo. Go figure. That's why I keep using the words BOOST SENSOR instead of pressure sensor. Just FYI.

I watched your video for the second time. That's two times more than I watch any video, but the part in the driveway indicates to me the pressure sensor is not seeing vacuum. OR maybe it's not a non turbo boost sensor. Is there a number on it? LIke N326? Or N327? Or N318?????

 

well... the sensor box has nothing on it, its just the little sensor box, and the vacuum line does have pressure, i pulled the hose from the engine, and i felt suction. but i guess my first order of business would be to reground the boost/pressure sensor?

 

IF the car is fully hot, and your sitting in the driveway, and you slowly rev to 3800rpm and over, does the engine get sluggish/sound funny when you reach that 3800 rpm figure? If not, the forget what I said about the secondarys coming online in the driveway.

I've done that in the driveway before (vac line off the sensor), and when the engine is rev'd slowly to the 3800 rpm figure you can't miss the sound of the secondary injectors coming online.

Yeah, try the grounding of the boost sensor. Looking in the wire side of the sensor, the gnd wire is on the top row, far right. It's either a brown/black wire or a pure black wire depending on build date. Most likely a brown wire with black stripe since it's a 86 car.

Never heard of hesitaiton in the driveway before. Like I say, secondarys don't come online in the driveway, only under Load driving and at 3800 approx.

 

well, its a lot worse when it is under load, but it still does it in the driveway as i showed in the video. but whats weird is i can give it full throttle all the way to 3800 and then it hesitates and makes an awful noise, like an ERRRRR!!! lol. but if i give it half throttle it will climb to the redline like normal. i can make another video if there is something u need to see, or maybe something i might have missed.

 

If the hesitation was JUST during driving, then I'd say do what others have done to get rid of the 3800rpm hesitation. That is to go to the ECU and find the ECU ground wires and solder an additional ground wire to them and put that new ground on a ring terminal and attach it to one of the studs that hold the ECU bracket in place. Works for me and works for some others. Did not work for some. Series four car only.

The grounds I'm talking about are on the small plug of the ECU and the middle plug of the ECU. Like you'd find the BLACK ground wires on the small plug.........then undo the wrapping on the harness and follow those wires up the harness about six to ten inches. There is where you'd find the ground wires for the ECU all soldered together in the harness. Then you'd solder a good new wire there and terminate that new wire on one of the ECU attach brackets.

But you say it happens in the driveway so frankly I don't know. Secondarys don't come online unless driving.....over 3800rpm....and a LOAD on the engine.

One a 86, those B wires shown in the ECU plugs are black except for the one in 2C which would be Brown/Black.

Hard to say what your problem is. Could even be someone *messed* with the internals of the AFM at sometime and screwed up the spring tension.

You description of using half pedal and reaching redline indicates the usual 3800 rpm hesitation that happens when the secondary injectors come online and at the same time the duty cycle of the primarys gets cut in half. Usually cured by adding the gnd mentioned above. I've a 87 that's now turbo but was non turbo. I can make the 3800 rpm hesitation come and go just by removing the extra gnd that was added as described above. Just unbolt my *new* gnd from the ECU bkt and the hesitation returns. Put the *new* gnd back on the bkt and it goes away. Works for me and some others........didn't work for some others.

I've no idea why yours hesitates in the driveway. Try adding a orifice for that problem.

 

oh ok, i will definitely give this a try, is there a tutorial on this anywhere? where is the ECU?

 

The ECU is behind a metal kick panel in the passenger foot well. You've got to unscrew the long plastic on the side, er, bottom of the door (not on the door itself, the long plastic along the bottom of the door frame, on the car) remove the plastic panels on both sides of the passenger foot well, then pull the carpet back and you will see the kick panel. There are 4 10mm nuts holding the panel on. It can be kind of a pain getting the carpet to pull back far enough to get access to all 4 nuts holding the panel on and getting it out, but it can be done, I assure you.

You will need:

phillips head screwdriver
flat head screwdriver
10mm socket / wrench

takes about 10 minutes max

 

i did this today, because i was having the same problem, and now my fc wont start!! i reversed the process, and it still wont start... no blown fuses/relays... it turns over... just wont try to crank... whats going on???? could i have fried the pressure sensor? would that keep it from starting? i used the black/white wire, and grounded it to the shock tower...im kinda worried now... please help!!

 

i did this today, because i was having the same problem, and now my fc wont start!! i reversed the process, and it still wont start... no blown fuses/relays... it turns over... just wont try to crank... whats going on???? could i have fried the pressure sensor? would that keep it from starting? i used the black/white wire, and grounded it to the shock tower...im kinda worried now... please help!!

 

oops...double post... could i have fried my ecu??

 

oh yea, its an 88 na

 

anyone??

 

^^^ first off, its not polite to threadjack. Second, it may take more than an hour for someone to responds sometimes, maybe longer for a threadjacker. And finally, third: did you plug everything back in? Including the battery? Start a new thread about this so that this guy can get HIS problem solved in HIS thread. There is no reason for you to re-ground some wires to the ECU and it not start, unless you messed something up. New thread.

 

Or better yet, SEARCH! I think I've seen a similar thread before....

 

i did search, and came up with this thread. i never meant to "threadjack" anyones thread... like i said... i searched and this is what i got. i dont think messing with grounds will fry an ecu either...but what if it wasnt a ground wire? what if this guy wants to know this happened to me before he does it to his car?? i would! im just looking to fix this problem, i love my car, and it hurts a little inside when something like this happens...lol and yes, i did hook everything up correctly, i even removed it when it wouldnt start... but nothing... im stumped as to what may have happened...

 

Good point, id go to rotorwiki, or fc3spro.com and get a factory service manual, then go to aaron cakes website and check to make sure that the wire you grounded was indeed a ground. But before you do that, unplug the afm, and plug it back in. Sounds weird, but try it.

 

Good point, id go to rotorwiki, or fc3spro.com and get a factory service manual, then go to aaron cakes website and check to make sure that the wire you grounded was indeed a ground. But before you do that, unplug the afm, and plug it back in. Sounds weird, but try it.

 

LOL a threadjacker, that is funny as hell, and original. but anyways, so where can i find a tutorial to reground my ECU?

 

how could I check if my ecu is still alive? I pulled the panel off of it to see if I could read codes off of it... But it doesn't give codes?? How do I check this thing??

 

Both of ya need to get a Factory Service Manual downloaded and start reading, lol.

 

do you have a good link for it?

 

The B/W wire is not the right one. It is power from the main relay. I know I had posted that before, but it was a typo and I F-ed up. The ground wire in the FSM is BLACK like Hailers posted, or for an '86 it might be BROWN or BROWN/BLACK. My fault for typing the wrong color, but in the future, always test wires with a multimeter to be sure you know what they are. And download your own copy of the FSM wiring diagrams to confirm anything if you're unsure (download FSM at the top of this forum). It's not even uncommon for wires to even be different colors from what the FSM says. There were variations between years.

With that in mind, I would think all that should happen is you would have created a short to the chassis. The wire you connected is very small gauge, and shouldn't be able to carry much current, so hopefully nothing was damaged. It would be like having some frayed wires touching the metal body. I haven't heard of it damaging sensors before, but I can't say for sure that it didn't happen. The pressure sensor should have just been unpowered at the time, since you diverted its power wire to the chassis. As for the ECU, it's not grounded anywhere near the the pressure sensor, so I wouldn't think it would come into play.

I would start by making sure your re-wiring of the B/W wire on the pressure sensor is good (solder or some good crimps). Check the underhood fuses with a multimeter for continuity. You can't just look at them. The EGI fuses being popped comes to mind from the symptoms you gave. Test the pressure sensor as per the FSM (I've attached a picture of the page). Pull engine codes to see if anything is acting up. Code checking link here: http://www.fc3spro.com/TECH/HOWTO/ER...KI/zerror.html

 

thanks rocket! ill have to make up a tester.