Wont rev past 4k easily

[Daeron]

the TPS either sends its signal or it doesnt; there is no "just enough" to do anything. if it contacts the right points at the right time, then the switch itself is (like you said) probably not the problem.. but the problem is still very reminiscent of a TPS issue, which would indicate a need to check the wiring associated with that circuit. if you have to, make one long lead for your multimeter, and check the continuity between sensor end and ECU end with an audible alarm, and proceed to flew every inch of that wire until you hear a break in continuity. This checks for intermittent connection where it should be. If THAT fails, then try a similar check, except mix up the terminals that you are checking (hit terminal A on sensor side, terminal B on ECU side and again, flex the wire, only this time, listen for a beep of continuity, indicating an intermittent short across that circuit.

 

Since you cleared up a major portion of the problem, it means that whatever is left is going to be intermittent, and difficult to track down. I call it "magic wire" syndrome; you basically have a gremlin somewhere chewing on something and need to find that beast and exorcise him.

 

In the end, the best way to proceed is in the precise order laid out in the EFI bible.. but dont forget that most of those tests are supposed to be run both AT the sensor, and at the ECU plug for the sensor, to confirm the integrity of the wiring harness.

[scottyMIz]

have you tried adjusting the afm? i had the same problems and it came down to a last desprite try and i took the cover off the adjusted the afm slowly one way then back the other way and it cleared up my issues. You are right the 76 efi does not have a cps it just senses a pulse from the coil i actually used the efi from my 76 280 on my mazda b2000 4 cyl engine and it ran like a top. In all honesty u can use that efi on anything with a single coil pulse and make it run good.

[Gollum]

My way of checking baseline AFM setting:

 

Pull off the cover to the AFM.

 

You'll see a little arm that spins with airflow that you can rotate easily.

 

Start the car. Test how much rotational play at idle you have in this unit until the engine starts choking. You should have about an equal length of play in each direction. There's also the idle air/fuel bolt that can be pulled out to allow more/less air to bypass the flapper. More air is lean of course, because it's unmetered air.

 

Generally you can set the idle air mixture to about halfway, then adjust the AFM to idle right in the middle of running rich/lean, and then you'll have a decent fuel curve providing you don't have any problems or modifications to the fuel system.

 

If you're injectors were bad/mis sized and the previous owner had been screwing with the AFM this could very easily be the source of your problem. If the system is completely 100% stock and has not been touched, then the AFM should be fine.

 

Hope you find the problem.

[jmt]

Thanks everyone for the help so far, I tried swapping the afm today, that didnt help on the top, but it did seem to run better over all after I got it dialed in, although I did put the old one back in just so Im not all over the board replacing and not realizing if I do fix the problem intermittently.. I still am in no better shape than I was, but Ill keep at it. -Josh

 

UPDATE: Believe I found it finally!!!! If I unplug the coolant sensor thats grounded it revs and actually goes!!! WTH is this sensor and what does it control, its not the coolant temp sensor (thats new) or the thermotime sensor its the one with one wire to ground on the block and the other goes to the wire loom its blue, then goes red after the connector. Thanks -Josh

[jmt]

Its back again, on the way home it was acting up again. Im at my wits end. I understand some of this now, I have a dual pickup distributor, so that switch controls my timing. searches didnt give me much as these dont seem to be all that common. It looks as though one of green wires is grounded on the dizzy. Can anyone enligten me on what I should do? Id like to get rid of the ballast resistor so can I get rid of one of the pickups or what? -Josh

[jmt]

Just because I hate when people dont post the resolution, im following up on this. Just an overview: I have a dual pickup distributor. The 2nd pickup has a switching relay located on the passenger side just under the fusible link boxes. Its controlled by a temperature switch with a blue and black wire coming off of it (not to be confused with the coolant temperature sensor). The black wire is grounded and the blue wire goes into the loom and switches to red via a bullet connector. I unplugged the connector thinking that the open circuit would be ok. I was wrong, it made the problem better somewhat but very sporatic past 4.5k. I grounded the red wire tonight and heard the relay switch over. My problem magically went away. Revs all the way up with no hesitation. I know this sounds simple enough but the car didnt run when I bought it so I had to look at every aspect of the car and start from ground zero on everything. So I suppose the permanent fix would be to replace the switch, but to be frank I dont really care. I just permanantly grounded it and called it good. Its one less thing to worry about. I dont think this system was used long (75/76) but to anyone having similar issues, I hope this helps. -Josh