Engine UPDATED WITH FIX IN POST #49 Help with sputter issue with cold starts

silverlx50

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Apr 4, 2007
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I am trying to diagnose a cold start issue. After the car sits for about 8 hours and it fully cools down, when i try to start it, it starts and then bogs down to about 300 rpm's and then it sometimes stalls. It will restart again and run until it warms up. If I restart while it is warm or hot. It fires right up.

I have found thay if I cycle the key to the on position three times it seems to help and sometimes will not stall out. I also noticed that when it is below 55*, it may stall twice. Car runs great otherwise.

I just replaced the fuel pump with a Wahlbro 255LPH pump and that did not resolve my issue.

I assume it must be an issue somewhere with the fuel pressure in the line maybe. Car has an old Vortech T Rex pump, 80lb injectors, stock fuel rails. Car runs at 38lbs on my autometer fuel pressure gauge and gets up to pressure as soon as I turn the key to the on position and the pump starts running.

Thoughts?
 
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93silverlx50

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Checked fuel pressure? Cold and hot.
I just monitor the auto meter gauge both cold and hot and it stays consistent. I don't think I had this issue before the quarter horse and tune so maybe something needs to be adjusted. Originally I was told my fuel pump wasn't holding the pressure after shutting the car down and that is why cycling the key on and off three times helped, it was additional priming
 

90sickfox

I didn't really have an issue with the stink...
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Temp sensor. Computer needs to see the temp to adjust for cold starts. Not the one for the gauge....the one on the heater hose pipe.
 

silverlx50

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Nice, thanks. Ill replace that. Mine is not very old, maybe 2 years, but that doesnt really mean anything.
 

90sickfox

I didn't really have an issue with the stink...
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It still could be another issue. Check everything thoroughly. Usually, there's a pretty easy test for temp sensors with a multimeter. Hate for you to spend money for nothing.
 

jrichker

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Too many people just throwing money at a problem. Listen to those voices that give you pointers towards diagnosing the source of the problem...


Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/
 

silverlx50

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Apr 4, 2007
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Too many people just throwing money at a problem. Listen to those voices that give you pointers towards diagnosing the source of the problem...


Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/

Ill pull the codes and see what comes up
 

7991LXnSHO

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I have Code 11’s and a similar issue where it idles roughly for the first minute or two, especially when below 55 f, then runs great. Following for help.
 

silverlx50

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KOEO (at full temp)
85 Canister Surge Solenoid Circuit Failure

10

29 insufficient Input from VSS
41 HEGO sensor signal out of range and no HO2S switching detected
91 HEGO sensor out of range / always lean
96 fuel pump secondary circuit fault / high speed fuel pump relay open

KOER (at full temp)
41 HEGO sensor voltage low / system lean
91 HEGO (HO2S) sensor voltage low / system lean

My car is a 93 LX. I was not able to find an orange wire for the O2 sensor heater ground but I did find a black wire coming from the injector harness that is bolted into the drivers side rear head. Id assume this is the O2 heater ground wire.
 
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silverlx50

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It still could be another issue. Check everything thoroughly. Usually, there's a pretty easy test for temp sensors with a multimeter. Hate for you to spend money for nothing.
I had an new sensor that I never used so I replaced that but the codes seem to say my O2 sensors are bad. They were replaced about 2 years ago, I think around the time the tune was done which is around the time the car started having this issue...
 

jrichker

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Well I swapped O2 sensors and no change at all.
How to clear codes.
Clearing the codes by pressing a button on the scan tool or disconnecting the test jumper used to start the code dump does not erase the “learned settings”. All it does is erase the stored codes in memory.

You must clear the codes anytime you replace any sensor. The following tells you how and is different from the method above
Clear the computer codes by disconnecting the battery negative terminal and turn the headlights on. Turn the headlights off and reconnect the all sensors including the MAF and anything else you may have disconnected. Then reconnect the battery negative cable.. This clears all spurious codes may have been generated while troubleshooting problems. It also clears the adaptive settings that the computer "learns" as it operates. Clearing the codes does not fix the code problems, it just gives you a clean slate to start recording what the computer sees happening.

Run the car for at least 30 minutes of driving and dump the codes again to assure that you have fixed the code problem or sensor problem. This is necessary for the computer to relearn the adaptive settings that the computer uses for proper operation. The engine may run rough at first, but should smooth out as it runs for the 15-20 minute learning period.


Code 41 or 91. Or 43 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

Revised 01 Sep 2019 1.) To emphasize do not attempt to measure the O2 sensor resistance. Disconnect the O2 sensor from the wiring before doing any resistance checking of the sensor to computer wiring.

Code 41 is the passenger side sensor, as viewed from the driver's seat.
Code 91 is the driver side sensor, as viewed from the driver's seat.

Code 172 is the passenger side sensor as viewed from the driver's seat.
Code 176 is the driver side sensor, as viewed from the driver's seat.

Code 43 is not side specific according to the Probst Ford Fuel injection book.

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:

"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.
When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.
Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the O2 sensor. Before checking the O2 sensor circuit wiring resistance, disconnect the O2 sensor from the rest of the circuit wiring. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage. End Quote

Testing the O2 sensors 87-93 5.0 Mustangs

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.


Disconnect the O2 sensor from the harness and use the body side O2 sensor harness as the starting point for testing. Do not measure the resistance of the O2 sensor, you may damage it. Resistance measurements for the O2 sensor harness are made with one meter lead on the O2 sensor harness and the other meter lead on the computer wire or pin for the O2 sensor.
Computer wiring harness connector, computer side.
88243.gif


Backside view of the computer wiring connector:
71316.gif



87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor

The computer pins are 29 (RH O2 with a dark green/pink wire) and 43 (LH O2 with a dark blue/lt green wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor

The computer pins are 29 (RH O2 with a Gray/Lt blue wire) and 43 (LH O2 with a Red/Black wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


94-95 5.0 Mustangs; note that the 94-95 uses a 4 wire O2 sensor.
The computer pins are 29 (LH O2 with a red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) to ground the voltmeter. . The O2 sensor voltage should switch between .2-.9 volt at idle.


Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer. Using the Low Ohms range (usually 200 Ohms) you should see less than 1.5 Ohms.



87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Dark blue/Lt green wire in the LH O2 sensor harness and the Dark blue/Lt green wire on the computer pin 43
From the Dark Green/Pink wire on the RH O2 sensor harness and the Dark Green/Pink wire on the computer pin 29


91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 43
From the Gray/Lt blue wire on the RH O2 sensor harness and the Gray/Lt blue wire on the computer pin 29

94-95 5.0 Mustangs:
Computer pin 29 Red/Black – LH O2 sensor
Computer pin 27 Gray/Lt blue – RH O2 sensor
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 29
From the Dark Green/Pink Gray/Lt blue wire on the RH O2 sensor harness and the Gray/Lt blue wire on the computer pin 27


There is a connector between the body harness and the O2 sensor harness. Make sure the connectors are mated together, the contacts and wiring are not damaged, and the contacts are clean and not coated with oil.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Check the fuel pressure – the fuel pressure is 37-41 PSI with the vacuum disconnected and the engine idling. Fuel pressure out of range can cause the 41 & 91 codes together. It will not cause a single code, only both codes together.

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness. The exception is that the 94-95 uses a 4 wire O2 sensor.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

Code 41 can also be due to carbon plugging the driver’s side Thermactor air crossover tube on the back of the engine. The tube fills up with carbon and does not pass air to the driver’s side head ports. This puts an excess amount of air in the passenger side exhaust and can set the code 41. Remove the tube and clean it out so that both sides get good airflow: this may be more difficult than it sounds. You need something like a mini rotor-rooter to do the job because of the curves in the tube. Something like the outer spiral jacket of a flexible push-pull cable may be the thing that does the trick.

If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.

Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs


Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs


Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs
 

silverlx50

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Apr 4, 2007
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I cleared the computer codes with the battery disconnected and headlights on.

Drove the car for 45 mins.

Fired the car up, no change. Still starts fine and sputters back down to 300 rpms and bounces way up and eventually evens out.

I still wonder if it could be an issue with the tune
 

jrichker

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I cleared the computer codes with the battery disconnected and headlights on.

Drove the car for 45 mins.

Fired the car up, no change. Still starts fine and sputters back down to 300 rpms and bounces way up and eventually evens out.

I still wonder if it could be an issue with the tune
Clearing the codes DOES NOT fix the problem that caused them. The tune is unlikely the source of you problem. It is whatever sensor, condition, or connection that tripped the computer and caused the codes to be set. TOD -Test, observe, and then diagnose - that's how you fix these cars. Remember TOD is your guide and friend

Read both code test paths and follow the instructions contained within them...
The O2 sensors have a detailed test procedure for checking the O2 sensor voltage output. Be sure to do it and not skip any of the steps.
 
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91GTstroked

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Jun 14, 2007
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Mine does the exact same thing as op. When it's about to die, I give it some gas and then it stays running. Only happens on cold starts and not all the time.
 

silverlx50

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Apr 4, 2007
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Noticed after driving the car for awhile, 1 hour or so, when I restart it hot, it starts fine but idles way low and seems not very responsive until I actualy put in first and driveway, then it clears up. After driving it long, it smells like gas and burns my nose.

When I loosen the gas cap it is under extreme pressue and takes maybe 5 to 10 seconds to release pressure. I swapped the fuel pump several weeks ago, none of the lines are crimped, the vent tube seemed fine.

I replaced O2's with Motorcraft ones and cleared and ran codes again today.

KOEO
85 (car doesnt have any smog stuff)
10
29 Continuous
96 Continuous

KOER
91

Second time I did KOER I got code 11, no errors and third time I got 91 again.

Tomorrow I will either swap O2 sensors around and see if the code changes to 41 or check using the suggestions...
 
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7991LXnSHO

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@jrichker Should bad O2 sensors have any effect on cold starts? Do you know what sensors besides temp EEC IV uses for open loop start ups? I am just guessing the TPS, IAT and coolant temp at least, but the O2 sensors should not work well cold.
 

silverlx50

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Apr 4, 2007
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So today I swapped O2s around. I drove the car for awhile, pretty hard. Ran codes again and got:
KOEO 67, 85, 10, 29 Continuous
KOER 41 AND 91

I hooked up a vacuum gauge at the tree in the A/C connection and get 7-8. At 2000 RPMs I get 14.

Im totally lost now
 
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