3500RPM Bucking, hesitation
 

Before some one rips me a new *!#%, I just spent the last few hours searching the threads for help on this.

I have an 86 Non-Turbo, body was stripped, painted cleaned... Engine was pulled from 87, ran good just had a miss at an idle.

All intake gaskets, vac lines ... replaced. 5th,6th port valves cleaned and now function. All body, engine grounding checked.

I have two problems; don't know if they are related. The first is I cant get the idle below 1000, second and more concerning is that at about 3500 RPM's (under load) the thing starts to buck, (not hesitate, like it's starving for fuel), it doesn’t seam to come back if I hold it. Just plain will not run above 3500.

I have check about all I could find in the factory service manual. Any help would be appreciated.

check the resistance on the injectors see if they match your old ones, also check the TPS. sounds like you may have a vaccum leak, like the line might be disconnected from the boost sensor or the sensor might be bad causing your high idle , let me know it that helps. goodluck, PEACE, EX...

it is likely it is the injectors i would check that route first

Re: 3500RPM Bucking, hesitation
 

When you replaced the Vac lines did you remove the orifice (pill) from the boost sensor line and put it in the new vac line? NO orrifice will cause the bucking under load at high rpm.

Not idling down sounds like a vacume leak on the intake.

Check injectors-I have the cutt-off problem, but if I hit the right spot, it bucks. My problem *probably* is the secondaries-they tested too low ohms. Replacing tommorrow.

I had the same problem, Be sure to check the vac. lines in between the upper intake manifold and the VDI manifold, there is a one-way valve (white and green) that is made of plastic. It can become brittle and one of the nipples can break off causing a vac. leak. After I took care of that the car ran great!:D

Re: Re: 3500RPM Bucking, hesitation
 

Sounds like you need a restrictor pill between your pressure sensor and manifold

Thanks for the relpies!!!

Did some digging and found that the original hose had no restrictor pill, but had a line from the A/T version I stripped, put it in made no difference.

I did some more digging and did a check of the Boost Sensor, supposed to have 2.5-3.5 V @ 3.9inHg vac. It was with in spec, however the thing does not hold any vac al all, SHOULD IT?

Also happend to have a timming light on the L1 plug wire and noticed that when the RPM's got to about 2000 it went out, anyone no if this is normal.

Did injector resistance check and voltage check, 2.1ohms on each secondary. Voltage ~12.5.

Found no vac leak still looking.

The big problem I am trying to solve is the hesitation, bucking, missing, sputtering... above 3500

Anyone have any more suggestions ?

yes, the pressure sensor should hold vacuum

Have a second one off a parts car, acts the same. Is this a typical failure part ?

I've seen 4 bad ones myself, so I'm not sure if that's typical or just coincidence. But it should hold vacuum, if it doesn't it's a leak.

I've got an 86 with the same problem. I can rev to 7k + with no load, but when I load it while driving, I cuts out at 3800. I'll reply if any of these work.

try reversing the direction of the restrictor pill.

what is the resistor pill i have the same problem my self and I have almost given up on it?????

Although I don't spool... I had the 3800 RPM hesitation fairly slightly. I scrubbed up my battery terminals and that made the difference. I love fixing shit without spending anything. Maybe it's the simple stuff ;)

Thanks for all the help. I finally did find the problem. One of the secondary injectors was bad. Was cutting out intermittently. As far as the pill, car runs great with or without it although Seems to respond better with out it. I could not find any reference to this pill in any of my microfiche with the exception of when the vehicle has an A/T.

How did you find out that the injector was bad? Is there a way to test my injectors if its cutting out intermittently? I am having the same problem and have changed out the resistor solenoid, pressure sensor, etc and nothing has worked. Thanks.

Anyone know?^

I am having the same problem but as soon as i rev it up it also backfires. problem started coming down the highway and blowing flames on a tailgater...i blew a few vac lines off but also i pulled my primary injectors outto put new ones in and i broke the little green caps that go over the nozzle.. would this cause the problem.. it also starts like shit

It's there. Atleast for the '86 N/A. Used the info from the FSM to make my own as I had thrown mine away (by mistake). .062 hole in a piece of plastic and jamed it into the line if I remember right.

Not having it didn't cause the 3800 hesitation it was more like 5K and only under load.

Glad to hear you found the problem. Just takes persistance.