Can't rev right

[DMC]

My car has an irregular idle with or without the MAF connected, but when the car is started with the MAF disconnected, as soon as it is plugged in the car seems to idle correctly but for only a few seconds. Without the MAF connected I could hold the engine @2000rpm no problem. With the MAF connected, i try to hold the engine @2000rpm and the rpm would steadily drop until the engine stalls. HELP PLZZZZZ!!!!!

PS I did try using a MAF that I know is good with no results!

[DMC]

ok after seeing other people did with similiar issues up here i bought a new (used) ecu and tried that. It did not change anything. Could someone please help, any ideas on what the issue may be would be greatly appreciated.

[NemeGuero]

KA? SR? RB? The more info you can provide, the better chances your problem will be solved.

[DMC]

This is true, the car is an 89 fb, i put the motor in its a 93 ka24de. i eliminated everything on the intake manifold except the AICV there is no ac no heat. there is no power steering, the motor ran fine when i pulled it from a friends wrecked car. it has a cone filter on it but no the whole long stock intake hose. I ordered a new fule pump that will be in tommorow, i will try to replace the fuel rail and injectors soon after if it doesn't work.

[TAMTANIUM]

check carefully for any leak and i mean really check it.

[DMC]

ok ill go buy new intake mani gaskets and redo the whole thing, do you have any other advice?

[NemeGuero]

check the regular shit.. vacuum lines, fouled plugs, clean the TB, clean air filter... and are you SURE the maf was good?

EDIT: did you plug the EGR hole on your mani?

do you have fuel pressure?

start trying to eliminate variables

[DMC]

everything on the intake manifold is plugged, i didnt check to make sure its not leaking yet though. I need to borrow a fuel pressure checker from the autoparts store to see if alll that is right. and yes the MAF was good it is on my friends running 240, thanks appreciate the advice, i will lok into some of it tommorow on my day off.

[NemeGuero]

Let us know what you find. I'll rack my brain some more if none of that helps.

[DMC]

ok well before i pull the intake manifold off i am going to replace the Throttle position sensor, it seems like that could be the problem. Im not sure how the ECU uses it, but it may be an issue. Does anyone happen to know how to check it before i buy a new one? also thanks alot for all the input!

[Steeles]

shot in the dark but you didn't mention.. your 89 was a SOHC you did switch to a DOHC ECU when you swapped right?

[NemeGuero]

I don't think the DOHC ECU connector would fit a SOHC ECU.. or vice versa..

[Steeles]

me either thats why I said it was a shot in the dark

[Nizzan4u2nv]

Sounds like a bad maf connector, the wires are probably loose. Check the maf voltage and the pins in the connector.

[95Kouki]

did you tinker with the positioning of the TPSensor since it was running out of your friends car? You might just have to re-position it.

From 240sx.org

<DOHC> TPS Testing and Adjustment

The TPS is there to tell the ECU how hard you have your foot on the gas. It isn't there to adjust for the idle. It's a sensor. It does have some adjustment of it's own and we'll try to give our version of what our Factory Manual says (though we won't even come close to doing it justice):

Throttle Sensor & Soft/Hard Idle Switch

The Throttle Sensor responds to the accelerator pedal movement. This sensor is a kind of potentiometer which transforms the Throttle Valve position into output voltage, and emits the voltage signal to the ECU. In addition, the sensor detects the opening and closing speed of the Throttle Valve and feeds the voltage signal to the ECU.

Idle position of the Throttle Valve is determined by the ECU receiving the signal from the Throttle Sensor. This system is called "Soft Idle Switch" and controls engine operation such as fuel cut. On the other hand, "Hard Idle Switch", which is built into the Throttle Sensor unit on the A/T equipped models, is not used for engine control.

Trouble Diagnoses:
1. Disconnect Throttle Sensor harness connector.
2. Make sure that resistance between terminal #1 and #2 changes when opening the Throttle Valve manually.
Looking at the "pins" of the connector w/ the locking tab of the connector pointing up, terminals #1 is the one on the LEFT. #2 is in the MIDDLE and #3 is on the RIGHT.

The results of the test should be:

Accelerator Pedal Condition Resistance in k Ohms
Completely released Approx. 2
Partially released 2 -10
Completely depressed Approx. 10
If test shows "No Good", replace Throttle Sensor.

Adjustment:

If Throttle Sensor is replaced or removed, it is necessary to install in proper position, by following the procedures shown below:

1. Install Throttle Sensor body in the Throttle Chamber. Do not tighten bolts. Leave bolts loose.
2. Connect Throttle Sensor harness connector.
3. Start engine and warm up sufficiently.
4. Measure output voltage of Throttle Sensor using voltmeter.
5. Adjust by rotating Throttle Sensor body so that the output voltage is 0.45 - 0.55 volts.
6. Tighten mounting bolts.
7. Disconnect Throttle Sensor harness for a few seconds and then reconnect it.

With the locking tab of the connector pointing up and looking at the back of the connector as the wires from the wire harness go into it, terminal #1 is the one on the LEFT. #2 is in the MIDDLE and #3 is on the RIGHT.

Output voltage is measured across terminals #2 and #3 from the harness side of the connector.

A&W

Question:

Do you know the procedure for checking out the TPS and adjusting the idle?

Answer:

For the full blown check, it has a few steps involving the ECU and it's connections to the TPS. We're going to skip those, assuming they aren't a factor. Also, trying to describe which terminal on the ECU harness to check would be a nightmare w/o a diagram. This is hard enough as it is!

Checking for the correct voltage, ground circuit, and resistance are not that tough. So here ya' go...

POWER SUPPLY:

Disconnect the TPS harness and look at the terminal side of the connector. (this is the side with the terminal connectors in it) With the locking tab pointing UP, the terminals are A, B, and C, from left to right. (Confusing, huh?) This is measured from the male half of the connection that goes to the engine.

Turn the ignition ON and measure the voltage between terminal C and ground. It should be approx. 5v.

GROUND CIRCUIT:

Ignition OFF. Check for continuity between terminal A and ground. Continuity should exist.

RESISTANCE:

Make sure that resistance between terminal A and B of the connector half (female) that goes to the TPS changes when opening the Throttle Valve manually.

The results of the test should be:

Accelerator Pedal Condition Resistance in k Ohms

Completely released Approx. 2
Partially released 2 -10
Completely depressed Approx. 10
If test shows "No Good", replace Throttle Sensor.

VOLTAGE ADJUSTMENT:

1. Loosen the 2- bolts that hold the TPS.
2. Start engine and warm up sufficiently.
3. Measure output voltage of Throttle Sensor using voltmeter.
4. Adjust by rotating Throttle Sensor body so that the output voltage is 0.45 - 0.55 volts.
5. Tighten mounting bolts.
6. Disconnect Throttle Sensor harness for a few seconds and then reconnect it.

Note: With the locking tab of the connector pointing up and looking at the back of the female connector as the wires go into it, terminal #1 is the one on the LEFT. #2 is in the MIDDLE and #3 is on the RIGHT.

Output voltage is measured across terminals #2 and #3 from the harness side of the connector.

Adjusting the idle is pretty straight forward:

Disconnect the TPS harness and turn the idle adj. screw on the IAA to get the car to idle at 650 rpm. Reconnect the TPS harness and your beloved should purr at 700 or so rpm. (The Factory manual gives a +/- tolerance of 50 rpm.) The IAA is at the back of the intake manifold. You can see it standing over the right (passenger side for N.A.) fender and looking at the funky device with the dime size recess for the adj. screw.


That or a bad MAF or huge vacuum leak

[DMC]

ok i checked the TPS and it is all good. I think it may have been unplugged the whole time though, the car still doesnt run right. Is there a way to reset it?

[NemeGuero]

disconnect the battery.. leave it off for at least a few hours for the harness to fully drain. that should 'reset' things.

or you can just try resetting the ECU:
Find the computer(Behind the plastic piece by the passenger foot
Pull it out
Turn your key to the on position
You will see a flathead screw looking bolt on 1 side of the computer. Turn this fully clockwise
Wait at least 2 seconds
Turn it back to fully counterclockwise
This will then show the trouble code - (The check engine light will blink to show this, for instance, blink..blink..blink......blink..blink, will be 32)
After you read the code, you can start the engine
Turn the bolt back to the clockwise position for at least 2 seconds(While running)
Turn it back to the counterclockwise position
Now shut the car and then start it again, this should of removed the code.

[DMC]

ok it seems to be revving "ok" now, i rev it and then it goes real low when i let off like it wants to stall. I will take it for a test drive tommorow and let you guys know.Thanks again for all the help!:bigok:

[Nizzan4u2nv]

Did you already set the timing?

[CoasTek240]

hey man, someone mentioned a bad maf connection. Not enough voltage, or a lose pin. I have to tell ya, i once ripped the connection off the maf, versus removing it properly and unscrewing it... on accident of course. it was one of those stupid ass mistakes. anyways. i got pushed all the pins back in and screwed it back on and it was working fine. i dunno if thatll help.

[mistaanime]

hmmm any check engine lights???

[thinkjdm]

i had the same problem with my swap. and i adjusted the timing and idle and tightened the gas pedal and throttle cable.

[NemeGuero]

read above guys.. he got the revving fixed already. Now his idle just needs some adjusting.

[DMC]

ok well the car still doesn't run right. I remembered i disconnected to TPS like a week ago. The car will not drive, it has no power and tries to stall. I am going to see if my check engine light is broke and go from there. Does anyone know if the coolant temp sensor has anything to do with the car running right?

[DMC]

ok the new maf didnt help it still runs horribly. Im not sure how much anyone will be able to helo threw the internet, but just incase here are how it is acting now. full throttle it will rev all the way up fine, partial throttle it seems to "studder" alot. It is hard to heep it at a constant rpm. when i try to drive it the car has no almost no power. when trying to drive it if i push in the clutch it normally stalls. ill add more if i think about it, if anyone can help its appreciated.

Also the check engine light doesnt work when you do a dohc swap apparently. There has to be a way to get it to work though, so i will try to find it.

[NemeGuero]

Distributor sounds like it's off.. bust out a timing light and check your timing.

[CoasTek240]

dave what happened, i thought the car was running fine a while back?
lemme know is i can help

[thinkjdm]

if your check engine light does not come on at the cluster..its because you only used the 5 wires to do a doch swap right? so...use the red wire thats for the CEL.

[95Kouki]

Try to pull the stored DTC off of the ECU via the LED on the ECU.

http://www.240sx.org/faq/articles/ecm_codes_doch.htm

And if the coolant sensor if faulty will definitely fuck some shit up...

CODE 13 - Engine Coolant Temp Sensor

Voltage Range should be... (.9-4.4 VDC) The More voltage the colder the sensor...it's a thermoresistor...resistance changes... (.2 - 9.9 kOhms) More resistance the colder...check your ranges w/a digital mulitmeter!

FSM Section EC page 97 (95 240sx)

Good Luck

[Nizzan4u2nv]

Try a different ECU.

[thinkjdm]

im betting its one of these....

1.check vacum leaks
2.have doch throttle cable
3.set timing
4.set idle valve

[TibDrifter]

first do a good tune up before you try to frind the problem. Seems like a igniting problem to me check for cap and rotars, and timing. good luck

[DMC]

Mass Airflow Sensor 12
Coolant Temp Sensor 13
Ignition Signal Primary 21
Throttle Position Sensor 43

I am guessing that the MAF and TPS are from me playing with it so much, I will disconnect the battery and see if they still pop up with everything hooked up properly. I will get a new coolant sensor from the junkyard asap, as for the other I have no idea.

[NemeGuero]

test the voltages as per FSM.. on MAF and TPS...

thats a lot of codes. Did this all happen suddenly? are you using the correct ECU?

[DMC]

It is alot of codes, but the coolant temp one is because i dont have a sensor hooked up, the maf and tps could be because i have started the car without them plugged in recently. as for the other, no idea.

umm well the car hasnt run right since installed the new motor. The codes were all on when i hooked up the light. I think the maf may be bad, the tps is reading fine. AS for the ecu, it is definatly a dohc ecu, but now that you mention it, i could have bought 2 ecus from automatic cars, does that matter? and how would i check?

[NemeGuero]

Ok, well get your coolant temp sensor and reset the ECU..

ignition problem might be because you're using the wrong distributor? Or don't have the right wiring harness connected to it?

No, the auto ECU won't change all that stuff. Your codes would be CPS and other tranny related sensors if you were using an auto ECU.. so thats not the problem.

There is a pdf file on jimwolf's website about ECU serial # matching.. its not complete but it might be able to give you the information you're looking for.
Its in the Tech section almost at the bottom of the page. I need to bookmark that link.. haha, I reference it soo much.