Huge Puzzle (engine surges depending on time / what is operating ???)

[KApwr'd510]

O.K. Here is the story,I have a 1971 Datsun 510 wagon that I have transplanted a 1995 240SX engine into. I beleive I have all the wiring set up correctly (I was an auto electrican for a couple of years, but that doesn't mean I know everything). The car starts and it comes up to about 1,200 rpm with a meter set at the green and black wire coming from the distributor and a little lower if I check it at the wire just past the resistor. At the green and black wire when it is warmed up shows about 750 rpm. The car has an external fuel pump. It is a T-Rex which puts out 50 gph @ 70 psi. Other than stock the car has an Injen intake and Hotshot header (cut and welded a bit to fit). I do not see the .09 volts at the ecu as the factory manual states I should see at pin 3 (to tach) I am only getting a reading of about .02 volts this is the reason for checking at the distributor. The only thing missing from stock is the EGR and the fuel canister as far as emissions go. I can run the car for about 10 minutes or so with no problem. If just at idle when the cooling fans come on the idle drops quickly but soon recovers(750 rpm to 800 rpm), but if I run the car for a short time and then rev the engine the idle will bounce from 600 rpm to 800 rpm for an extended period of time until I hold the idle up for about 10 seconds and then it returns to the 750 rpm to 800 rpm and holds steady. The bouncing rpm can also happen when all the lights are on and the coolant fans kick in, this can also be remedied by holding the rpm's up for a short time and the idle will return to normal, but given a few short blasts on the throttle will bring back the bouncing rpm's. Sorry about the long winded explination. Does anyone out there have any ideas about what is causing this, suggestions as to what to check, etc. This is my first time dealing with an ECU and fuel injection and I must admit it is doing a pretty good job of kicking my butt. I have checked as much as I can outside of fuel pressure only because I don't have a gauge. If I can provide more information just let me know. The car runs like a rocket powered go- kart it is just the crazy bouncing idle at stop and sitting in traffic that is killing me.Thanks,Joe

[574-240sx]

Auto or manual ECU? I still have an auto ecu in my car and the same problems you describe happen to me occasionally.

[KApwr'd510]

Manual, I tried another ECU and had the same results.

[KApwr'd510]

Anyone have any ideas? Starting point to check?

[s13sr20chris]

try adjusting the idle screw in both directions. sometimes the idle will be set too high or low and the ecm gets all funny. you may also want to pull your iacv-aac apart and clean it. also, try unplugging the alternator just for haha's.

[KApwr'd510]

OK I'm finally going to have a chance to try your suggestions this weekend. Do I need to unplug anything while playing with the idle?

Any idea why I am not getting the correct tach signal from the ECU?

Thanks,Joe

[s13sr20chris]

the tach reads incorrectly? no, i guess i missed that. if you are refering to the .09v, i have never run into that. if the rpm is accurate i would not worry about it.

[KApwr'd510]

OK I had to drop this problem for a bit while I had my radiator fixed and some honeydo's to take care of.

Here is the results:I turned the idle screw both ways unfortunatley I did not realize how easy the screw would move (should it move that easy?) so I do not know how far I turned it. I did close it all the way once and the car stayed running (TPS still plugged in) then I brought it back to another spot and the idle remained at 750 or so and the surging went away. Now I would like to adjust it according to the FSM. Correct me if I'm wrong I need to bring the car up to operating temp - unplug the TPS - set the idle - plug the TPS in and life should be good.

New question?Since I am not getting the correct out put from the ECU to run the tach where should I hook up the tach? Do I hook it up to the green/black wire coming from the distributor or on the other side of the resistor to the yellow/black? Any one out there with a clue as to why I don't see the .9 volts the FSM says should be coming from pin 3 on the ECU for the tach?

Second new question?My temp gauge is not working properly. I have read the FSM and it says I should see 70~90 Ohms at 140F. I'm seeing 700 Ohms. I bought another temp sender and tested it in water. I'm seeing about the same readings as the old sender, is the sender messed up or is the FSM wrong?

Thanks for the help,Joe

[KApwr'd510]

Anybody with some answers or ideas on my last post?????Thanks,Joe

[NISTECH]

Idle adjustment procedure is correct except the car must be off when unplugging the TPS and when you go to plug it back in.

I havemnt had to deal with the tac signal at the ECU either so I dont have an answer on that . Where ever it was you found an accurate signal I say use that for your tac.

What sensor are you testing the 2 wire or single wire sender. The single wire is for the gauge.

[KApwr'd510]

Hi,Thanks for the reply. I'm testing the single post sensor (yellow wire to gauge). If the FSM is correct then the sender is bad because the gauge reads properly if I put the yellow wire to ground with resistors in between the wire and ground. If the FSM is wrong I'll need to find a work around to correct the gauge (doesn't move much look like the car is always cold).

As far as the tach goes hooked to the green and balck coming fron the distributor seem accurate. Before I hook it up thereI'm going to check that I haven't missed some wire or another at the ECU (its a possibility I have missed something). With daylight getting shorter it gat a little more difficult to check.

Thanks,Joe

[NISTECH]

Joe take the snder wire and short it to ground. does the temp gauge do full hot? If so you have proven the gauge is capable of working full range and all the wiring to it is ok. at that point you should replce the sender. also though be aware if you have an air pocket in the cooling system and no fluid is hitting the sender it will give the illusion the car is cold.