Finally, I can pull codes

RYC CUKR

Founding Member
May 19, 2002
1,437
1
38
Orlando
Finally got the new A9L in and figured out why the car had an intermittant miss at part throttle. Ended up having a bad plug but I am glad I did cause I probably wouldn't have found that I also had a crapped out ECU otherwise.

I pulled the following codes.

12 Cannot control RPM during ER self test high rpm check

34 EVP failed above the closed limit of .67

42 No HEGO switching detected always rich (right side)

95 Fuel pump secondary circuit failure

I am pretty square with everything except for the code 42.

For code 12 I probably need to clean or replace the IAC, for 34 I believe that I need to clean or replace the EGR valve (let me know if I am wrong on this one) and for 95 the guy who did the MAF conversion never wired in the fuel pump signal.

Code 42 is my concern. The car does run rich and I have seen some posts in the past on what can cause this other than a bad O2. I would prefer to check before I go throwing parts at it.

I tool FP readings and its 43 with vacuum off and capped and about 39 with the vacuum connected. The FPR is a stocker. The car pulls 12" of vacuum which I think is a little low but it does have an undetermined cam that was put in by the previous owner. I went through with TB cleaner and tried to find any vacuum leaks and couldn't find any.

Where should I be looking next?

Mods to the car are as follows: TFS trackheat intake, 70mm TB and EGR spacer, 76 MM C&L MAF, unknown cam, 3G alternator upgrade, BBK full length headers, O/R H pipe and Dynomax bullets.

I have most of the original parts like TB, MAF etc so I can swap them back on if need be.
 
  • Sponsors (?)


Code 42 & 92 (engine running) System rich - Fuel control or (memory) System was
rich for 15 seconds or more (no HO2S switching) - Fuel control. Look for leaking injectors,
fuel pressure too high, cylinder(s) not firing due to bad ignition.
Testing the O2 sensors
Measuring the O2 sensor voltage at the computer will give you a good idea of how well
they are working. You'll have to pull the passenger side kick panel off to gain access to the
computer connector. Remove the plastic wiring cover to get to the back side of the wiring.
Use a safety pin or paper clip to probe the connections from the rear. The computer pins
are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire).
Use the ground next to the computer to ground the voltmeter.

Fuel pressure OK, the injectors are not firing, OR one or more injectors stuck
open

Do a cylinder balance test: Warm the car's engine up to normal operating
temperature. With the Engine Off, Key OFF, use a jumper wire or paper clip to
put the computer into test mode. Start the engine and let it go through the
normal diagnostic tests, then quickly press the throttle to the floor. The
engine RPM should exceed 2500 RPM's for a brief second. The engine will shut
off power to each injector, one at a time. When it has sequenced through all
8 injectors, it will flash 99 or the number of the failing cylinder such as 22 for
cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause
the test to re-run with smaller qualifying figures. Do it a third time, and if the
same cylinder shows up, the cylinder is weak and isn’t putting out power like
it should. See the Chilton’s Shop manual for the complete test procedure

The red wire on each injector is powered up whenever the ignition switch is
in the Run position. The computer provides a ground to complete the circuit
and fire the injector. The injector must have a ground to squirt fuel on
command. A short to ground in the injector return wiring can cause one or
more injectors to be continually open or triggered
A.) A Noid light available from Autozone, is one way to test
the injector wiring. If the light stays on constantly, either the wiring has a
short to ground or the computer has failed

B.) I like to use an old injector with compressed air applied to the
injector where the fuel rail would normally connect. I hook the whole thing
up, apply compressed air to the injector and stick it in a paper cup of soapy
water. When the engine cranks with the ignition switch on, if the injector
fires, it makes bubbles An injector stuck open will release a continual stream
of bubbles. Cheap if you have the stuff laying around, and works good too.
The same trick works great to find leaking injectors too.​
The wiring for the injectors may have some bare spots in it causing the
injector to computer control wire to ground out. This would cause the
injector to remain on anytime the key was in the Run position. Remove the
injector wiring connectors from the injector. Note that each injector has one
red wire for power and a non red wire (wire some color other than red) for
computer controlled ground. With the key off, disconnect the computer
connector from the computer. Use an Ohmmeter between the non red wire
and ground. You should see more than 100000 (100K) ohms resistance.


See the following website for some help from Tmoss (diagram designer) &
Stang&2Birds (website host) for help wiring http://www.veryuseful.com/mustang/tech/engine/

Diagram courtesy of Tmoss & Stang&2birds

88-91_5.0_EEC_Wiring_Diagram.gif


Using the above diagram, check the resistance between the injector and the
computer. Clean and check the 10 pin connectors since they are a potential
trouble source. Any resistance greater than 1 ohm between the injector to
computer wire and the matching pin on the computer connector is a problem.

harness02.gif


See http://fordfuelinjection.com/?p=6 for more help

Here's the link to dump the computer codes with only a jumper wire or paper
clip and the check engine light, or test light or voltmeter. You’ll need it to do
the cylinder balance test

See http://www.troublecodes.net/Ford/

index.php


index.php


IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method.
There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

attachment.php


89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

attachment.php
 
Alright,

I took some volt readings on the O2 sensors at the computer connector.

With KOER I read .44v on pin 29 and .01 volts on pin 43. So this would seem to me that I have a bad 02 on the pin 43 side and it is causing the car to run rich.
Pin 43 is the drivers side 02 sensor. I checked the wiring to from the ECU to the 02 sensor connection and the signal wire is good. I also rang the ground wire and it is good and there is 12v on the power wire when the key is in the run position. I am going to swap the 02 sensors to make sure it is the sensor and not something in the wiring that I have overlooked.

I didn't have any of the stuff to check the injectors so I put my fuel pressure tester on. Ran the car and then let it sit with the key in the run position for a while and the pressure hadn't really dropped at all so it doesn't seem that fuel is leaking through the injectors.

I tried to do a cylinder balance test but I keep getting a code 77 which is that it didn't see WOT during the dynamic throttle response test. Not sure what the problem is there.