Still a Couple Bad Codes

[Blown88GT]

29C - Insufficient input from vehicle speed sensor.
66C - MAF sensor went below 0.4 volts during the last 80 warm-up cycles.

Since the battery was connected, spent time trying to set the base idle, so these may have been stored at that time. The following day, it was road tested & no longer died when rolling to a stop. Cold idle was erratic. Warm idle was 950rpm. Fully warm idle was about 700 rpm. May never get better with 30lb injectors, 76mm C&L MAF, 9AL EEC. At this time, there is no FMU & no "tune". FMU is out for analysis, possible repair, probable replacement.

Not sure why 29C is coming up, never had it before.
VSS is connected to the EEC. O/Y to pin-6 (VSS Gnd); DG/W to pin-3 (VSS hot). These are new wires that make the connection at C350 at the connector at the left hadn cowl where the VSS connects to the Speed Control Amplifier (p.104, EVTM). The interesting thing is the O/Y & DG/W go into the connector but no wires go out to the SCA. I have cruise (speed) control, so don't know why this is.

66C could be because we were attempting to set the Base Idle.

Computer is on the floor, MAF is buried inside the passenger side fenderwell. Have to remove battery to unplug connector. I've seen connector extensions, might have to get one.

Will test according to this at the computer:
Code 66 MAF below minimum test voltage.
Insufficient or no voltage from MAF. Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF. This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables.

The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

Changes in RPM causes the airflow to increase or decease, changing the voltage output.. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow.

Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

At idle = approximately .6 volt
20 MPH = approximately 1.10 volt
40 MPH = approximately 1.70 volt
60 MPH = approximately 2.10 volt

Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 10K ohms between either pin C or D on the MAF wiring connector and pins A or B. Make your measurement with the MAF disconnected from the wiring harness.


Tuning recommendations are not in the future, so please no recommendations to do so. I'm doing this "old school", there were no tunes & no dynos 20 years ago. Worst case, it's a Megasquirt.

 

[jrichker]

Clear the MAF code by disconnecting the test jumper while dumping codes, or follow the instructions for your code reader. Or, disconnect the battery and turn on the headlights. That will wipe the computer's memory and erase all the stored data, including any "learned" parameters.

Seeing your background is electronics, find an oscilloscope and connect it up to the wires on computer pins 3 & 6. If the oscilloscope is A/C power only, put the car up on 4 jackstands. Start the car, put it in gear, and slowly bring the road speed up to 60 MPH as you watch the scope display. Note any extreme variation in signal strength or loss of signal. If you have a battery operated oscilloscope or a power converter, skip the jackstands and do the test while driving the car. That's a better idea, I always get a bit nervous running 60 MPH while on jackstands.

No oscilloscope, do a continuity test between the VSS wiring connector the wires on computer pins 3 & 6. You should disconnect the computer's main wiring connector from the computer when doing the test, It is much easier to do that way. You should see less than 1.5 Ohms: be sure to jiggle the wiring and look for breaks or loose connections when you do the test.

 

[Blown88GT]

Found 2 things I did not like:

1. The EEC ground was in the location shown, but the body ground to the battery negative was missing. This occurred when the battery was moved from the driver's side to the passenger side. A 2AWG battery positive cable goes from the battery, in front of the radiators to the starter relay. The negative cable is also a 2AWG to the engine on the passenger side with a pigtail from the negative to the passenger side ground above the headlights. Therefore the computer ground relied on the body for the ground return to the battery. I have re-established the computer ground directly to the battery by splicing a 10ft 10AWG from the battery negative to the body ground pigtail & removing the pigtail from the battery to the passenger side ground. This will establish a single point ground which the EEC might be sensitive to; not sure how a non single point ground might affect it. I'm pretty much the expert in grounding & shielding of circuits that I designed & provided to DoD but can't say the same for Ford. Since they used a single point ground, I suspect they had a reason, but maybe not given Ford's history of electrical blunders.

I had forgotten it was there because it is obscured by the supercharger compressor inlet hose.

2. The breather tube was connected by a hose to a location near the K&N filter. This does not provide a free flow of air through the crankcase to the PCV when vacuum conditions exist. The reason it was moved from the original location, i.e. breather tube to throttle body, is under boost, the throttle body is pressurized & you don't want to pressurize the crankcase. It is now connected by a port to the inlet hose after the K&N filter & before the compressor inlet, so the crankcase will always be at a pressure less than the throttle body.

Both 1 & 2 may be contributing to the surging idle. Never had a problem with 19lb injectors & stock 55mm MAF & A9S EEC. Now have 30lb, 76 mm MAF & A9L.

I no longer have an o-scope or access to any that function, but will try the continuity test on pins 3 & 6. Been attempting to follow the Vss circuit on the Ford Wiring Diagrams (not the EVTM) & it's nearly impossible to trace the circuit from page to page. Haven't used the speed control in years, so not sure if it even works. I supposed if it doesn't that would indicate a bad Vss sensor? This would indicated the Vss failed within the past 2 months, because I've only seen that code the past 2 times. At least the Vss is not too expensive:
http://www.latemodelrestoration.com/item/LRS-9731B/83-93-Mustang-Speed-Sensor
Shouldn't be too difficult to replace.

I have a pair of new O2 sensors, but haven't installed them yet.

UPDATE:
Found intermittent bad connection where I tapped into the Vss signal at the harness in the engine compartment. With 60-pin removed from EEC, pin 3 to 6 reads 206 ohms, solid, even with jiggling the wiring at the splice. Where did you get the 1.5 ohm figure? When I never had the Vss signal connected, EEC never showed a bad code for it. My 60-pin had pins 3 & 6 empty. From what I understand, certain Ford vehicles (Lincoln, Crown Vic) used the EEC for cruise control, others (Mustangs) used a cruise control module. This would explain the empty pins.

BTW, the >10k ohm reading for the MAF pins C to D (signal to return) reads 3.86K ohms on 3 different sensors. I supposed you got the 10K from Probst? I will have to call that value into question based on my readings. I installed a 4-pin Ford connector between the MAF connector and the EEC because the MAF is now inside the fenderwell & not accessible without removing the battery. All connections are soldered & shrink wrapped.

I tried the jackstand thing once. Made me too nervous. Reminded me of a 3-Stooges clip. Why would you need 4 jackstands, when 2 is enough?

 

[Blown88GT]

MISSION SUCCESSFUL
1. A little shakey on startup.
2. Successful takeoff.
3. One minor issue on cruise.
4. Successful landing.

1. From cold start with 80deg ambient, had to feather throttle for a few minutes to keep it from dropping too low & stalling. I would not define this as surging, but as hunting.
2. Tremendous power even without boost; blowoff valve diverting some of the flow.
3. When warm idle will go no lower than 1000rpm. Cruise control works, so nothing wrong with Vss.
4. After 5 minute heatsoak, it will idle about 700rpm.

Only codes are 11-O, 10, 11-C; all good.

I may be trying one of these: http://www.latemodelrestoration.com...Mustang-50L-58L-Idle-Air-Control-Iac-Adjuster
Have you ever hear of turning the IAB Valve upside down? It might be worth a try.

Still can get a couple pounds of boost at partial throttle in 4th. Awaiting rebuilt or new FMU before attempting WOT for extended time periods.

 

[jrichker]

The Mass Air conversion requires you to run 2 wires from the VSS sesnor or the VSS controller to pins 3 &6. The 1.5 ohm figure is the amount of resistance that you might see in a typical old automotive harnress, naturally the lower the better.

I would disconnect the supercharger and bypass it to work out the kinks in the idle and low speed range. Once the engine's idle and low speed performance is solidly fixed, then add boost. The old computer fixer's axiom of " shorten the buss until there is only CPU, memory, console I/O and disk controller" works in the automotive world. This follows the troubleshooting principle of removing as many varibles as possible before troubleshooting what's left.

The http://www.latemodelrestoration.com...Mustang-50L-58L-Idle-Air-Control-Iac-Adjuster works for some cars and not for others. It allows you to add more air to bypass the throttle and eliminates having to tinker with the TPS when you change the airflow by adjusting the throttle stop screw. Twist the throttle stop screw up too much and you can easily get past the 1.1 max voltage at rest and set a code 23.

AC doesn't control idle properly: look for +12 volts at the IAC red wire. Then check for continuity between the white/lt blue wire and pin 21 on the computer. The IAC connector contacts will sometimes corrode and make the IAC not work. The red wire on the IAC is always hot with the engine in run mode. The computer provides a ground for the current for the IAC. It switches the ground on and off, making a square wave with a varying duty cycle. A normal square wave would be on for 50% of the time and off for 50% of the time. When the idle speed is low, the duty cycle increases more than 50% to open the IAC more. When the engine speed is high, it decreases the duty cycle to less than 50% to close the IAC. An old-fashioned dwell meter can be used to check the change: I haven’t tried it personally, but it should work. In theory, it should read ½ scale of whatever range you set it on with a 50% duty cycle. An Oscilloscope is even better if you can find someone who has one and will help.

Recommended procedure for cleaning the IAC/IAB:
Conventional cleaning methods like throttle body cleaner aren’t very effective. The best method is a soak type cleaner used for carburetors. If you are into fixing motorcycles, jet skis, snowmobiles or anything else with a small carburetor, you probably have used the one gallon soak cleaners like Gunk or Berryman. One of the two should be available at your local auto parts store for $22-$29. Take the solenoid off the body and set it aside: the carb cleaner will damages some types of plastic parts. Soak the metal body in the carb cleaner overnight. There is a basket to set the parts in while they are soaking. When you finish soaking overnight, twist the stem of the IAB/IAC that sticks out while the blocker valve is seated. This removes any leftover deposits from the blocker valve seat. Rinse the part off with water and blow it dry with compressed air. The IAC/IAB should seal up nicely now. Once it has dried, try blowing through the bottom hole and it should block the air flow. Reassemble and reinstall to check it out.

Gunk Dip type carb & parts soaker:

Setting the base idle speed:
First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. Then the electrical signal through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPM’s to 650-725 RPM’s

Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

This isn't the method Ford uses, but it does work. Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks.

See the "Surging Idle Checklist” for more help with all your idle/stall problems.

 

[Blown88GT]

The 206 ohms I was seeing from pin 3 to pin 6 was with the Vss connected. That seems to be in the ballpark for that type of sensor. Since the cruise control functioned, held 55 mph on a straight away & no Code 29, the Vss is operating normally. Besides there is no indication that the computer even knows if it's connected. I didn't have it connected for several months & the computer never generated Code 29.

Disconnecting SC has no affect on anything, much of the flow is being bypassed at idle by the blow off valve (aka, surge valve). You can feel the air being vented.

Besides, idle is fine when warm, not fine when cold. ACT & ECT sensors are new.

The IAC is working, it's just not fast enough until the engine is very warm. Maybe the actuator shaft is sticking when cold. Will try lubing it with Corrosion Block which has brought all kinds of electrical devices back to life for me.

BTW, a lesson in electrical engineering is not necessary; I have 2 degrees in EE & more than 30 years of practical experience.

 

[jrichker]

The 206 ohms I was seeing from pin 3 to pin 6 was with the Vss connected. That seems to be in the ballpark for that type of sensor. Since the cruise control functioned, held 55 mph on a straight away & no Code 29, the Vss is operating normally. Besides there is no indication that the computer even knows if it's connected. I didn't have it connected for several months & the computer never generated Code 29.

Disconnecting SC has no affect on anything, much of the flow is being bypassed at idle by the blow off valve (aka, surge valve). You can feel the air being vented.

Besides, idle is fine when warm, not fine when cold. ACT & ECT sensors are new.

The IAC is working, it's just not fast enough until the engine is very warm. Maybe the actuator shaft is sticking when cold. Will try lubing it with Corrosion Block which has brought all kinds of electrical devices back to life for me.

BTW, a lesson in electrical engineering is not necessary; I have 2 degrees in EE & more than 30 years of practical experience.

I'm 66, and have been diagnosing and fixing complex electro-mechanical systems for 48 years now. That includes everything from cars (48 years) to computers (34 years) to airplanes ( 11 years). In there somewhere is a two year electronics degree and enough computer class certificates to cover a wall. The PWM explanation was more for the benefit of those who may be reading along and trying to understand what's happening. I'm not just here to advise you on fixing your problem, but to help others gain understanding of how it works.

 

[Blown88GT]

...I'm not just here to advise you on fixing your problem, but to help others gain understanding of how it works.

I thought that might be the case. I would be interested to see how many others actually wade through all the details you provide. I'll wager most don't.
You've got me on the age by a few years, a lot more on cars (although did work on an electric car when they were still school science projects), about the same for computers & aerospace (aircraft engine controls, Defense Dept. R&D, special US Navy projects). There's Facility Engineering in there, too.

The locking tab on the IAC connector broke, so it's off to the salvage yard to find a replacement. Gave the IAC a good dosing of Corrosion Block. Have you ever used it? It's amazing stuff. Safe for all electrical.
http://www.learchem.com/products/corrosion-block.html
Click on the Truck Applications.