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93 Northstar 4.6 hodrod high idle


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On Monday, December 12, 2016 at 0:30 PM, BodybyFisher said:

If this is a 93, you have an ISC motor that controls the return to idle along with speeding up the idle when the pcm senses increased load like the steering pump drag while turning .  The motor or mechanism may be sluggish or slow returning to idle or it is adjusted too far out.   The plunger should not touch the linkage stop when the throttle is closed.   Does it click?, if so it might be shot, replace it. The grease also dries up inside.   Inside the unit is a closed idle contact that retracts the plunger when the throttle linking stop contacts the end of the plunger. 

Check for vacuum leaks also, that show themselves up the rpm range.   On the top of your throttle body is a sensor (I don't know its name and don't have time to look up what it is), it has 2 hoses attached to it that I have seen crack, that is unmetered air that will boost the idle, I have seen them crack very tight to the larger black hard plastic.   Inspect that closely for cracks it might be the MAP. 

Observe the ISC control, for lagging.  

What did Westers say about the idle increasing in closed loop?   Is that fixed?   When the idle increases, is it increasing because the ISC plunger pushes the throttle open? 

See this thread if you have not seen it already, I started it back in August and it includes a link to Barry who did a fantastic dissection of an ISC, it should be illustrative.

 

It seems that its the isc keeping the idle up.  So this time after doing the cooant fixes it didnt jump up in rpm after going into closed loop but right from startup its idiling around 1000rpm and not going down.

From reading the manual the computer is only suppose to control the isc when the isc plunger is making contact with the throttle and its internal TP switch (not to be confused with the TP sensor) is activated.  When the throttle is bumped and the TP switch inside the ISC is now open circuit the ecm is set to not activative it.  i belive in my case it might still be and the ISC is extending a little with throttle bump and when the throttle returns its taking a moment to return to idle.  Anyway, I've checked voltages and ohms  at the ISC as per the manual and the original reads 40ohms accross the motor terminals and the newer parts store replacement is 80ohms!  Book says above 3ohms it should be replaced so ill try another tomorrow.

Question:  What voltage with the throttle plates closed should the TP be and what percent open should the throttle plate be?  right now its 0% open and TP is 0.41volts according to the scanner with the ISC removed.

Setting the ISC - when it's fuly retracted so you can set the gap (0.45"?) should it be out just enough that the internal TP still clicks on and off if you push the end of the plunger or fully back so internal TP switch is off?  

I think Im going to also go back and try the original bin flash from Westers.  I have three that we were trying each a little different to try and fix issues but i cant say what changed in each exactly.  Maybe some thing got changed that shouldn't.

Thanks for the advice on the Holley setup but probably not going to happen at this point.  

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The contacts inside the ISC are the closed throttle contacts, when you take your foot off the gas, the linkage stop hits the plunger closing those contacts and that action causes the plunger to retract.   You can push the ISC with your finger and the ISC should retract.  If there is a .045 space, the internal closed throttle contacts should not be closed.    I hope I am understanding you correct.     Good you are going to try a new ISC.

I need to go into my manual to look at the throttle position switch.

The OBD1 had a minimum air adjustment, did you see that in the manual?, its a base idle, that is really low, like 400 rpm, I need to find it.

Ill come back later. 

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39 minutes ago, BodybyFisher said:

The contacts inside the ISC are the closed throttle contacts, when you take your foot off the gas, the linkage stop hits the plunger closing those contacts and that action causes the plunger to retract.   You can push the ISC with your finger and the ISC should retract.  If there is a .045 space, the internal closed throttle contacts should not be closed.    I hope I am understanding you correct.     Good you are going to try a new ISC.

I need to go into my manual to look at the throttle position switch.

The OBD1 had a minimum air adjustment, did you see that in the manual?, its a base idle, that is really low, like 400 rpm, I need to find it.

Ill come back later. 

"The contacts inside the ISC are the closed throttle contacts, when you take your foot off the gas, the linkage stop hits the plunger closing those contacts and that action causes the plunger to retract."  -  Understood, but here is my question, at idle, throttle pushes against ISC plunger which activates the internal "closed throttle contacts" or as the manual calls them the TP switch.  When the throttle is moved and off of the plunger the TP opens and the ISC is suppose to stay put correct?  My issue,  I rev the motor, (not even extremely fast), so the throttle stop is off the ISC plunger but the plunger extends itself a bit so when the throttle returns it hits the plunger and is at a higher rpm than stock for a second or so before the plunger slowly returns it back to the RPM idle it was at.  Like a momentary delay idle return.  Is this normal??

ISC setting - When setting a new or old ISC the procedure is to retract the ISC plunger fully, then set a gap of 0.045 or 0.30?  I thought earlier it was recommended 0.045"?  When the plunger retracts fully and can't retract further the internal TP switch contacts should be closed correct, and this is the set point where you set the gap from correct?

I'll have a look for the minimum idle air speed, these service manuals are a bit hard to navigate.

Off topic, I noticed that the ECM requires a 12+volt high signal all the time on the "power steering high idle request" pin to function normally, otherwise if the pin sees a low the ECM thinks the power steering high idle bump is requested and increases the idle.  I never though to check if this was mistakenly left floating or tied to ground by mistake.  Something to check tomorrow.

 

 

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NO, its not the retraction, that closes the contacts, its the slight push by the linkage.  When it it fully retracted, the contacts are STILL OPEN.  With its retracted, push the plunger with your finger and you will notice that it moves IN slightly, and THAT is when the contacts close.

When you adjust the gap, don't physically push the plunger in, retract it fully, by pushing the plunger in to make the contacts close, then disconnect the plug.....then set the .045 gap. 

Good point about the steering input, when you are sitting still, and turn the steering wheel, the PCM ups the idle when you turn the wheel to offset the pump load. 

Is this car using the Northstar steering rack?

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17 minutes ago, BodybyFisher said:

NO, its not the retraction, that closes the contacts, its the slight push by the linkage.  When it it fully retracted, the contacts are STILL OPEN.  With its retracted, push the plunger with your finger and you will notice that it moves IN slightly, and THAT is when the contacts close.

When you adjust the gap, don't physically push the plunger in, retract it fully, by pushing the plunger in to make the contacts close, then disconnect the plug.....then set the .045 gap. 

 

Perfect!  You answered the question I had, sorry if I wasn't explaining my question correctly.  Reason I was asking is I can't get the ISC to retract by pushing it, it sits solid against the throttle at idle, the contacts closed already.  If I understand you right the plunger should move back if this is the case?  Anyway, I've been using a 9v battery to retract the plunger on the bench but it moves it ALL the way back so there is no movement at all, no slightly in or out to make the clicking sound and open/close contacts.  My bad.  So there is one thing, the ISC was not adjusted right.  This setup drives me nuts, I'll take a IAC solenoid any day over this. :P

I'll look tomorrow and see about the power rack setup but I'll be surprised if the original owner installed the Cadillac setup, and if he did, if it wasn't done correctly.

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Yes, when the throttle hits the plunger, it should retract.  You can disassemble it and clean the contacts, they might be pitted or burned.   In the threads I provided you, there are photos of the contacts and internals for you to look at.

The ISC works in the OBD1 setup very good, in August I replaced an ISC and no adjustment was necessary, just kept the plunger at the same length as it was.   The IAC works invisibly and I never had a problem, other than a dirty port.   You are right the IAC is less problematic, but you have a unique situation there.  

Ill do some bedtime reading for you.

Do you have the 93 or 94 factory service manual?

 

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Ok, on page 6C-18 in the 94 FSM, is a description of the Throttle Position (TP) Sensor.

This statement is made, The PCM provides a 5 volt reference signal and a ground to the TP sensor and the sensor returns a signal voltage that changes with the throttle valve angle.

At closed throttle (close to zero degrees) the TP sensor output signal is low (below 1 volt) and at WOT (approximately 85 degrees) the TP sensor output signal is high (approximately 5 volts).   Your voltage at around a half a volt with the throttle closed sounds good, what is it at WOT?

Because the TP sensor is NOT adjustable, the PCM must account for build tolerances that could affect TP sensor output at closed throttle.

The PCM uses a learning algorithm so that is can correct for variations of up to six degrees of throttle angle. 

The PCM uses TP sensor information to modify fuel control based on throttle valve angle. 

Acceleration enrichment occurs when the throttle angle increases rapidly (similar to an accelerator pump on a carburetor, (I remember these going bad and getting a BOG or hesitation on acceleration)). 

Given that your throttle at idle is resting on the plunger, and you are going to change the ISC, we will have to wait for the results of that change. 

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27 minutes ago, BodybyFisher said:

Ok, on page 6C-18 in the 94 FSM, is a description of the Throttle Position (TP) Sensor.

This statement is made, The PCM provides a 5 volt reference signal and a ground to the TP sensor and the sensor returns a signal voltage that changes with the throttle valve angle.

At closed throttle (close to zero degrees) the TP sensor output signal is low (below 1 volt) and at WOT (approximately 85 degrees) the TP sensor output signal is high (approximately 5 volts).   Your voltage at around a half a volt with the throttle closed sounds good, what is it at WOT?

Because the TP sensor is NOT adjustable, the PCM must account for build tolerances that could affect TP sensor output at closed throttle.

The PCM uses a learning algorithm so that is can correct for variations of up to six degrees of throttle angle. 

The PCM uses TP sensor information to modify fuel control based on throttle valve angle. 

Acceleration enrichment occurs when the throttle angle increases rapidly (similar to an accelerator pump on a carburetor, (I remember these going bad and getting a BOG or hesitation on acceleration)). 

Given that your throttle at idle is resting on the plunger, and you are going to change the ISC, we will have to wait for the results of that change. 

Just got to the shop and waiting for parts.  Question,  recomended spark plugs and gap for theae motors?

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The Power Steering Pressure Switch description is located on page 6C-20 of the 94 FSM. 

Here is a summary:

The power steering pressure switch is located on the power steering hose between the power steering pump and rack and pinion gear.   The power steering pressure switch is normally closed and provides a battery voltage signal to the PCM with NO power steering load.  When the power steering pressure increases to a calibrated level due to steering load (such as full steering lock), the switch opens and causes the signal voltage to the PCM to drop to 0 volts.

The PCM uses the power steering pressure switch signal for IDLE SPEED CONTROL during high steering loads to maintain a stable idle.   A shorted steering pressure switch may cause a stumble or stall during steering loads and an OPEN switch should set a PCM trouble code.

If you are not using the OEM rack setup.....the PCM sees an OPEN......increasing the IDLE...... that could be why the ISC is not fully retracting, the PCM thinks your steering is turned to the lock position and its upping the idle...   You can fool the PCM by jumping the appropriate terminals on the PCM to imitate the normally closed power steering pressure switch. 

Let me know if you need more info on the PCM, pins for this.

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Page 6D4-21 of the 94 FSM states:

Spark Plug Type -- AC Delco 41-900 or equivalent, the gap is 0.050 in. and torque to 11 lb. ft.

By the way, the 93 and 94 engines are very similar.

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1 hour ago, BodybyFisher said:

Page 6D4-21 of the 94 FSM states:

Spark Plug Type -- AC Delco 41-900 or equivalent, the gap is 0.050 in. and torque to 11 lb. ft.

By the way, the 93 and 94 engines are very similar.

Thanks.  So the power steering input on the ecm was left open.  He doesnt have a rack in this car so im going to tie the pin high.  Can you tell me if Red connector pin A6 is ok to jumper for power input?  it appears to be an unused ouput with +12 with key on.

Thanks on the plugs.  They had some ngk irridiums in it that dont look to hot and the gap is way out.  I really hate troubleshooting someone else's mistakes, lol.

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1 hour ago, BodybyFisher said:

Ok, on page 6C-18 in the 94 FSM, is a description of the Throttle Position (TP) Sensor.

This statement is made, The PCM provides a 5 volt reference signal and a ground to the TP sensor and the sensor returns a signal voltage that changes with the throttle valve angle.

At closed throttle (close to zero degrees) the TP sensor output signal is low (below 1 volt) and at WOT (approximately 85 degrees) the TP sensor output signal is high (approximately 5 volts).   Your voltage at around a half a volt with the throttle closed sounds good, what is it at WOT?

Because the TP sensor is NOT adjustable, the PCM must account for build tolerances that could affect TP sensor output at closed throttle.

The PCM uses a learning algorithm so that is can correct for variations of up to six degrees of throttle angle. 

The PCM uses TP sensor information to modify fuel control based on throttle valve angle. 

Acceleration enrichment occurs when the throttle angle increases rapidly (similar to an accelerator pump on a carburetor, (I remember these going bad and getting a BOG or hesitation on acceleration)). 

Given that your throttle at idle is resting on the plunger, and you are going to change the ISC, we will have to wait for the results of that change. 

Hmm, with only 6deg of allowable correction the throttle plate could be adjusted out of that range really easily and still have the tps under 1 volt.  Some of the vacuum ports in the throttle body are either inside or outside the throttle plate with only a few turns of adjustment so I'm still unsure where it should technically be set.

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Ok, let me ask again, do you have a factory service manual?

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I am looking at the description and schematic for P040 in the FSM page 6E-A-142.

The power steering pressure switch receives 12 volts on terminal B from a 10 amp fuse located at D1, in the underhood relay center.

The pressure switch is always passing current, (normally closed), and the switch opens when pump pressure increases to 450 to 650 PSI.

The switch sends 12v to the PCM at terminal 1A5 on an orange/black wire off terminal A at the pressure switch.  1A5 is located on the RED connector, viewing the PCM connector looking AT the PCM side, with the connector locking mechanism facinig up, 1A5, is described as connector 1 (RED), Row A, the top row looking at it in the orientation I described previously and pin 5 or the 5th pin from the LEFT.  The pins and rows might be marked, I don't know.

Have fun.

I think I provided you with the PCM pin diagrams but if you don't have a key, let me know.  Ill need to scan it.  

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53 minutes ago, BodybyFisher said:

I am looking at the description and schematic for P040 in the FSM page 6E-A-142.

The power steering pressure switch receives 12 volts on terminal B from a 10 amp fuse located at D1, in the underhood relay center.

The pressure switch is always passing current, (normally closed), and the switch opens when pump pressure increases to 450 to 650 PSI.

The switch sends 12v to the PCM at terminal 1A5 on an orange/black wire off terminal A at the pressure switch.  1A5 is located on the RED connector, viewing the PCM connector looking AT the PCM side, with the connector locking mechanism facinig up, 1A5, is described as connector 1 (RED), Row A, the top row looking at it in the orientation I described previously and pin 5 or the 5th pin from the LEFT.  The pins and rows might be marked, I don't know.

Have fun.

I think I provided you with the PCM pin diagrams but if you don't have a key, let me know.  Ill need to scan it.  

Hi, my 93 GM service manual has it on page 6E-A-128.

I should have mentioned that the previoys owner used a Ron Frances Telivok 3 wiring harness to wire this motor.  At the moment there is no connection to pin 1A5 and no wires coming from a under hood fuse block and steering switch so the ecm is probably thinking the open pin means there is a load on the system.  If I fool it with a 12v input to 1A5 it should think there is no load im assuming.  My phone isnt allowing uploads.  I'll try later when i get in.

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I am thinking that is a reasonable assumption, she may settle right down.

You can not believe the boost to idle when your turn the steering wheel lock to lock.

You mentioned the Ron Frances wiring harness in your first post. 

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10 hours ago, BodybyFisher said:
8 hours ago, BodybyFisher said:

I am thinking that is a reasonable assumption, she may settle right down.

You can not believe the boost to idle when your turn the steering wheel lock to lock.

You mentioned the Ron Frances wiring harness in your first post. 

Welll I got it put back together and gave it s go before leaving for the day and nothing has chdnged.  New ISC still seems to extend out from idle.  The throttle is very touchy and tevs up quick, too quick, and doesnt idle down right away still.  When i get back to it Friday I'll start again and check for vacuum leaks etc.  very frustrating.

Now that the coolant system is setup right i may have opened a can of worms.  What are the signs of a bad head gasket on these cars that aren't obvious?

 

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Did you jump the steering pressure switch circuit?

You said there were ports plugged on the throttle body, can you take a photo and post it here?

I use a Balkamp block tester from Napa to test for a bad head gasket, you may need to order it from their on line store or have them order it in.  It is about $50

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2 hours ago, BodybyFisher said:

Did you jump the steering pressure switch circuit?

You said there were ports plugged on the throttle body, can you take a photo and post it here?

I use a Balkamp block tester from Napa to test for a bad head gasket, you may need to order it from their on line store or have them order it in.  It is about $50

I jumpered 1A5 to 12v key on.  I'll double check the circuit voltage while running tomorrow.  It doesn't seem like it had any effect but I'm going to try another one of the earlier BIN tunes from Westers and see if it changes.  I remember asking him about this high idle a while ago and he changed a few things, of which I'm not sure but they didn't seems to help.

I'll take a photo of the TB and lines off it tomorrow.

Off the top of your head do you know if the coolant that flows through the TB is a closed internal flow through design system or if it has gaskets that seal it to the manifold separator block between it and the manifold.  No sure if that statement made any sense.

Has anyone successfully removed the ISC from their motors?  I it would throw codes and not be happy but if the idle was set with the throttle plate screw and the ISC removed it sure would relieve this whole ISC BS.  I don't like to ever do stuff like that but in this case I'm considering it but probably cause a whole host of other issues.

It's a real bi*ch trying to run and tune this car as it's -35c and the car can't be moved so the garage door needs to be opened to evacuate most of the exhaust.  Nothing like working on a car in a huge winter coat and thick gloves, lol.

 

 

RFH.jpg

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Do me a favor, idle the engine with the ISC removed.

Ill do some thinking on your last post

That photo really illustrates the mess you have on your hands wow

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4 hours ago, BodybyFisher said:

Do me a favor, idle the engine with the ISC removed.

Ill do some thinking on your last post

That photo really illustrates the mess you have on your hands wow

I'll let you know how it goes tomorrow.  I'm at a point where I'm seriously considering just using the ISC as a stopper for the throttle body arm to set the idle at a nice RPM and disconnect the thing.

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1 hour ago, crackerjacc said:

I'll let you know how it goes tomorrow.  I'm at a point where I'm seriously considering just using the ISC as a stopper for the throttle body arm to set the idle at a nice RPM and disconnect the thing.

:lol:

Don't loose patience yet.   Look, we figured out the steering pump pressure switch.  It has not defeated us yet.  

Are you using the OEM coolant tank?

At some point maybe we can speak over the phone, it might help.

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1 hour ago, BodybyFisher said:

:lol:

Don't loose patience yet.   Look, we figured out the steering pump pressure switch.  It has not defeated us yet.  

Are you using the OEM coolant tank?

At some point maybe we can speak over the phone, it might help.

So when it goes into closed loop I get the following codes all of which are expected and shouldn't cause issues other than throwing a code according to the manual.  There is no - Trans axle, Body control module, factory cruise, or traction control unit on this setup.  The bin is supposedly for a manual car so I'm not sure why the trans axle code are being thrown.  The only one that "might" be of concern is 59, Trans axle temp.  Obviously it's an open circuit now.  I believe if I jumper-ed the 5v reference and the input pin it would stop but as i said it doesn't seem to affect anything other than throwing a code I believe.

I'm using an aftermarket surge tank and set everything up like the factory.  Unlike before there is now constant flow in the main part of the system and the rad section only flows when the thermostat opens.  The fluid appears to flow in the surge about an inch or more above the inlet line and out into the heater hose T.  So far so good.  I did put a higher PSI cap on the radiator (18~20) compared to the surge tank which is stock 16 psi because in the factory setup the rad is a closed system not normally accessible and you don't want it's cap pressure to pop before the surge circuit does it's thing. ;)

I'm going to check the intake manifold bolts tomorrow and see if they are loose and if it's not too much of an issue possibly replace the plenum gaskets.  Not sure how far the owner wants to go with this car, rumor has it he's selling it at some point in the next year. :(

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I looked at the manual and dont see anything that can kick up the idle.

Can you get real time data off the pcm?

Do you have 2 heater hoses connected to the crossover?, starting at the bottom of the coolant tank?

Does the purge line flow coolant?

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Oh man, eyes are going to roll and you might laugh after this.  My number one rule is to never trust someone when they say the motor is all good but in this case the motor wasn't showing the usual signs of issues.  I made the call to pull the intake since everything was point to a vacuum leak that the computer was fighting to control but we couldn't find doing the usual tests.  Well I'd say just about every intake port showed signs of blow by on the gasket surface!  I'll assume that at some point someone just tried to tighten the intake down to fix the issue but by then the gaskets were toast.

Anyway, tomorrow I should have it back together and see how she runs.  Now I have to decide if I should go back to the original tune purchased from Wester's, I probably should as the point of it's following bins were to try and tame the idle which I'll assume will be easier now that the MAP won't be going nuts causing the ISC to go nuts causing......

To answer your question I believe I have the coolant system setup as close to stock as possible.  It appears to flow as intended from the factory.

Yes the scanner can read the data stream in real time.  It's a huge help!  Just no ECU BIN modding capability, I'm just able to burn files to the EEproms I installed.

 

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