long story short, it was the atmospheric pressure sensor on the right-side of the passenger kick panel. Looks just like a boost sensor (well, so it is).

After almost a year of searching and hard work to my car (87 base), I finally managed to fix the 5-6k rpm hesitations. Now, whenever I would run the car at around WOT, as soon as the tach hit between 5000 and 6000 rpm, the car would lightly bump several times (lack of power).

Now, I did everything immaginable to try to fix the problem, but to no avail. EVERY sensor tested out to specs, the fuel system was very healthy, and the injectors were working as they should (I even checked the spray pattern, and after a little cleaning [more on this later], they were perfect).

So, now I was left stumped. The only thing I didn't check under the hood was the water temp sender (for the gague) and the oil pressure sender. Both those appeared to be working correctly and are irrelevant to this problem. ANYHOW, I thought that it HAD to be the computer (ECU/EGI/ECM/PCM/whatever). I replaced it several times, and to no avail. Tried two N326's and one N327. Neither fixed the problem.

So it must be a gounding issue. Nope. I grounded everything with a spare harness I had from my 86 parts car (it was pretty ratty, but all the connections were sound; I tested them). Didn't fix it. What else?

I removed all the emissions stuff and made block-off plates for the ACV and EGR valves, as well as the sub-zero start assist. Totally removed the vacuum rack, and removed the pulsation damper (used a spare banjo bolt from the parts car). It didn't hurt anything, but didn't help either.

I replaced EVERY sensor under the hood with different ones, different injectors, different coils, you name it, it got replaced. Literally. Now, at this point I just began to accept the fact that my car had a stumble and that was it. Then I got a crazy idea....

What about the atmospheric pressure sensor near the passenger side kick-panel? Well, since I was going to be down there, I figured I may as well put my original wiring harness (it didn't have the grounding mods done to it) back in as well. So, I replaced the atmospheric sensor with the one from the parts car (which, btw, did not have a label on it, but just painted-on numbering).

I started it up, I wasn't expecting anything, and BAM! Problem solved. Now, keep in mind that the original harness had the hesitation every bit as bad as the modified harness.

Oh, a simple way to clean the injecors for almost nothing is to just take a can of brake parts cleaner and a can of PB B'laster, attach the little red straw, press it aginst the pintle cap and spray it for a few seconds with the PB. Let it sit for a few hours, then do the same with the brake-parts cleaner. This works wonders, though it MAY damage the injectors (they haven't failed for 2 years, and I cleaned the hell out of them). If you want to un-freeze an injector, use a 1.5v bettery and a pair of alligator clips. (or an old injector plug). If it refuses to unstick, briefly (and I mean briefly; brush the alligator clip across the terminal) bump it with 12v. It doesn't matter the polarity of the wires.

Anyways, hope someone finds this helpful,

Matt

 

Thank you for posting this. Many times we never know how people fix their cars after porting their problems.