N/A boost sensor and hessitation.
 

My cars been doing a hesitation thing lately but more in the 4-5K rpm range. It is more pronounced when the car is cold but is still there a little when warm.

I found that if I disconnect the vaccume line going to the boost sensor (this is a N/A car remember) that the hesitation goes away COMPLETELY. Couple of questions.

1. What would be bad If i just left it disconnected forever.

2. what would cause this?

I don't think it would be the grounds as with the vaccume line to the boost sensor disconnected the secondary injectors should be firing and it runs great.

Educate me.

what boost sensor???

Justin

The factory service manual, when talking about a n/a engine, calls it a boost sensor. When they talk about the turbo model, they call the same item the pressure sensor. Go figure. Mounted on the right fwd strut tower. Black in color. One electrical plug and one vacuum line going from the bottom of the sensor to the intake manifold. The item tells the ECU how much load is on the engine so the ECU can make adjustments to timing and other performance items. I think they call it a MAP sensor on other cars. If you disconnect it I think, don't know, that it goes to a default setting. That ought to bump you to the top so someone can answer the question.

Try doing it again- just to be sure.
Did you cap the line off, or just leave it open?
If it runs better with the vacuum line open, then you are running too rich- a sensor problem maybe.
If it disapperars, and the line is capped, just leave the line off- it does no damage, except you may experience SLIGHTLY lower mileage (probably <1mpg)
Do you have any problems getting your idle up? If so, it's running too rich.
It's usually electrical- I was experienceing the exact same problem, it would come and go. I got hesitation between 5000 and 7000.
I added another ground at the firewall/engine ground- it cleared my problem up.

ALSO- to those who remember my S-AFC problems... adding another, heavy ground from the engine to firewall, and from the ground wire on the SAFC (on the chasis side of the double AFC grounds) to the chassis totally cleared up my problems about running like crap at part throttle and when cold. I'll post more details in a seperate post in a minute.
Good luck.

Bambam7- Good point. I did just pull the line off and did not cap it. I only had taken it for a short drive. By the way my car idles fine and even with the line pulled idled only a little higher rpm.

However,...last night I pulled the line off and caped it and the drive to work this morning was SWEET!!!! No hesitation what so ever. Guess I must have a bad boost sensor. Unless anyone can think of a big problem with leaving it disconnected (I can live with lower MPG) I think it'll stay that way for a while.

From what my repair manual said it seems the secondary injectors don't operate below 2500rpm regardless of what the boost sensor signal is so I don't think it will affect Idle.

Maybe some other peoples N/A are having same problem?

was the hesitation consistant or was it just at specific rpms? i have a little hesitation at 4k then again at 5k and then again at 6k and can't figure out why i think this could be it but my sensor can't be bad i just had the thing checked out by a good rotary mechanic and everything was fine think maybe it's just a grounding issue?

It was in a couple spots but worst was around 4k. It must have been fairly consistent because I found myself anticipating it on the drive in this morning but then it wouldn't happen :) .

Samething is happening to me. What would happen if I left the vacume line off?
The car is rev happy to 8k now.

I have a similiar problem, but it's more like a 3600 rpm restrictor. I thought it was my actuators not openeing (wich they were not), but wired them open, still didn't help. Tonight, I'm going to install some grounds and replace the fuel filter. If that doesn't work, I'll try taking the bs vac line off.

test your engine code to see if u have bad sensor

My computer didn't show any codes. It's an '86 so it may not beable to tell.

I plan to try and test the boost sensor and wiring to tell exactly what's going on. I don't expect mine to be wiring problem because the engine wiring harness is less than a year old (bought it new from mazda). I expect it is the actual boost sensor.

For now I'll leave the boost sensor off line and enjoy the smooth strong reving engine. The car just screams through the upper rpms again.:D

By the way I am not saying this is a fix for all the hesitation problems just something else to check (and easy to check).

That is an easy one. I also own an '86 and checked the codes-no codes at all :). I'm also going to check boost sensor,injectors, and injector connectors.

Oh, my pressure sensor went bad... It would give me codes when it was cold as balls outside (like 30 fahrenheit), otherwise I would not have known. I tested it as the shop manual suggests and it was off-spec. I replaced it with a "new" (read: new to me) pressure sensor and she ran better.