REDFC3S86

My n/a 86 has been hesitating between 3-4k lately......I have 2 tps's and both of them give me the exact same reading on my digital multimeter....i set the tps at 1 with throttle closed, but as i open the throttle, the highest it reads is 1.4 or so.....The DMM shows these readings with either tps installed.....any ideas?

HAILERS

Fully warm the engine up.

Leave ALL connectors connected.

Meter put on DC volts.

Negative lead on a good gnd like the alt body or batt neg post.

Backprobe the green/red wire on the TPS connector. The green/red is in the half of the TPS plug that is connected to the EM harness.

Key to ON, engine OFF with a fully hot engine.

Meter should read approx 1vdc. If not, then adjust the screw til it reads 1vdc.

Now move the throttle linkage to open. The meter should read 4.5 to 5vdc when the throttle is open.

How did that work out for you?

REDFC3S86

Thanx for the reply hailers...ill give that a try as soon as i can.

REDFC3S86

When i adjusted the tps to spec, my idle got really weak...around 500rpm and it would almost cut off, but keep itself running......I could turn the adjustment screw a quarter turn cw and the idle would stabilize, but when revved to 3-4k, the engine would break up and hesitate. Any other ideas?
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HAILERS

The 500 idle when fully warmed up is a sign of the BAC not being functional. BAC would normally overcome the 500rpm and up it to approx 750 rpm at idle. The BAC usually fails because its transistor inside the ECU goes **** up because at some time the two wires of the BAC plug have come together and fried the transistor.

The transistor is replaceable and is a TIP 120 or some such number and can be had from Radio Shack for a buck twenty or so. Needs soldering in the ECU board.

The TPS does NOT set the idle. The TPS defines ZONES of operation for the ECU. At idle the TPS should output a VOLTAGE of 1vdc approx. Like 0.95vdc to 1.05vdc would be APPROX. That one volt approx can be observed with ALL ELECT PLUGS ATTACHED and back probing the green/red wire in the harness side of the TPS plug with a meter set on dcvolts.

The 500 idle speed can be upped some by adjusting the screw in the top of the dynamic chamber and some adjustment of the Variable Resistor near the afm area of the car. I'd do the screw on top of the dynamic chamber first.

There's a writeup on the transistor somewhere and I Might add it later.


http://www.radioshack.com/product/in...ductId=2062617

Another very common fix for non working BAC is it's electrical plug. Pull it off. Look inside the harness plug. Sometimes one of the two sockets is PUSHED BACK inside the plug and is not making contract with the pin inside the BAC's jack. If so, then shove the socket from the wire side til it's even with the other socket in the elect plug and reattach it to the BAC and see how things work NOW.

REDFC3S86

Thanx again for the words of wisdom Hailers! I'll take ur advice and look into the BAC

REDFC3S86

I did look into the BAC....unplugged the connector and it looked fine inside. I also let the engine warm up, reset the TPS to spec (idle stayed stable), then i disconnected the BAC again....there was no change idle speed/quality. Shouldn't the idle change with the BAC connector disconnected? And BTW, the weird hesitation/misfiring hasn't gone away. I also want to clarify exactly what the engine is doing under part throttle....From 3-4k, the engine seems to be breaking up/maybe misfiring repeatedly.....Its not a single pause or "break" in revs but numerous breaks....Whether i hold the throttle at a fixed position (and keeping the rpms steady) or slowly open the throttle gradually to cause rpms to rise between 3-4k, the engine doesn't rev smoothly like it should.....There's numerous little interruptions within this particular part of the rev range......It will also periodically hesitate slightly past 4k.....the engine will rev past this 3-4k area with slightly more throttle....its just not smooth....Can anything else be causing this? I'm starting to doubt its the TPS

HAILERS

I doubt it 's the TPS also. Remove the plug from the TPS and rev the engine. Probably the same result will happen. Although removal of the plug will cause a minor change in the idle probably 'cause the ECU defaults to a given zone when it sees a lack of signal from the TPS.

Series for TPS is at full extension prior to the secondary throttle plates opening. Very little movement of the pedal will cause the TPS to go to it's full extension.

You talking about reving in the driveway, are you not? NOt on the hwy? I've no real solution for.

REDFC3S86

Yeah revving while in neutral at a stand still and while moving in gear the same thing happens..........very strange....looks like i'm gonna have to take the manifold off and look at the injectors, vac lines & wiring to see if i notice anything obvious.....It could be the primaries, but the engine idles fine...if it was fuel, you'd think the idle would be off as well...idk

skir2222

I had almost the same exact problem, turned out that I had the incorrect ballast, and my wiring harness seemed to have a break in the primary injector wires causing a hesitation only under 3k rpm under light throttle.

REDFC3S86

Did you just cut the break and splice the 2 wires back together? And what's this ballast you speak of? Thanx for posting. That'll give me something to look for.

dennis blackstone

hailers the two wires to the bac where do they come from ..mines are missing could you show me how to rewire to my ecu ...so i can plug it in ....i dont even no the colors of the wires they are missing

flipkc

I have this similiar problem where I have a bunch of small misfires at very light throttle and it was diagnosed as a faulty TPS. There is a dead spot that was caught by a true rotary specialist that works at ForceFed Performance locally. I'm going to get a used working TPS installed and report back. My car is a 91 JDM T2 btw.

I also have the low idle and I'm assuming the BAC just needs adjustment. I'm hoping it's not a transistor in the ECU.

I'll report back after I get a known working TPS installed as well as adjust my BAC.

midnightbluefc

iTrader: (19)

i had hesitation like that when my water temp sensor on the neck broke, replaced it and it fixed it....