hey guys and gals, having that stupid 3800 rpm crap on my 87tII. went to fc3s.org and did what they recommend on their tech tips list. when i saudered the ground wire to the upper left terminal of the boost sensor wire harness my friggin car would not even run. cut the wire and it ran fine. anyone know a simple solution to the 3800 rpm hiccup?
thanks, josh

 

recheck your soldering job, check that nothing is touching that shouldnt, recheck to make sure you had the right wires etc etc

 

thanks for the tips. the solder joint is fine. the wire is not contacting anything else. i soldered the ground wire to the upper left brown wire just like they said on fc3s.org and grounded it on the body.
josh

 

It could also be a loose or disconected injector plug.

 

On a 87 it should have been a brown wire with a black stripe. I've been told that on 88 cars the wire should have been a pure black wire. If it were another color, its the wrong wire. No way, if it were the brown wire with a black stripe, that the car would not start. Its just a ground. I have two 87 cars. One turbo and one n/a. Both have an additional ground spliced to the brown wire with a black stripe. EDIT: This might be of interest http://home.earthlink.net/~burntoast/3700.html

 

i went out and pulled the wire harness to the gang plug up and found that it was spliced, so maybe my upper left ground is the black wire now, (maybe someone replaced it with an 88 harness?) i'll give it a shot and appreciate the input.
josh

 

Could be. I have a 87 and there is a brown wire with a black stripe, a brown wire with a white stripe, a black and white wire and a brown and red wire. Black and white wire should have 12v approx, the brown and black is a ground(yours seems to be black now)the brown and white is the output to the ECU and its output should vary according to the vacuum on the intake, and the brown and red wire is a ref voltage(I believe) of something like 4.5v. If you have a meter and want to know if that sensor is working write back and we'll see what we can do or go to http://www.iluvmyrx7.com and download the fuel section of the 88 manual and it gives a checkout of the sensor. I worry that you might have whacked your sensor when the wrong wire got grounded.

 

i guess i do have the 87 configuration, the wires you described are the exact same ones i have. the brown and white wire is the one that i grounded, i didn't ground the brown and black wire because it was not in the upper left hand corner(that's what fc3s.org said). guess i should get stuff confirmed that i get off of the internet. if i did mess up my sensor, what kind of symptoms would be displayed? if you are considering my lack of boost, it was present before i tried to do the grounding. it occurred right after i installed my af ratio and boost guages, my hiccup at 3800 rpms also occurred at this time.
lots of thanks, josh

 

Oh! After reading your last post, I realized that all one has to do to confirm the working, is to look at the stock boost gauge. See if when the key is turned to on, that it moves. And then drive it and see if the boost gauge responds to boost. There is a checkout of the sensor in the manual where you get something like a Mittyvac to put a given vacuum on the sensor, and then you read the output of the sensor on the brown wire with a meter. If your gauge works that seems good enough to me. Have fun.

 

Sorry to bother you again but....I went out to my 87na and undid the extra ground that I had added to the boost sensor and then read the ohms. It read .8 ohms without the extra ground. Reading from the brown and black wire to the neg post on the battery. I reconnected the extra ground and made the reading again. Its was .1 ohm. So the extra ground is needed. The .8 is unacceptable. I had the hesitation problem with this particular car and it went away after the introduction of the extra ground at the boost sensor. You might want to make a resistance check after you do the extra ground to make sure its .1 or less b/t the batt neg terminal and the brown and black wire.