1990 Lx Runs Like Crap!

[tsc]

Hi, all. Just came over from an "other" mustang forum... Was a member over there for quite a while and got fed up with the lack of helpfulness and knowledge. It seems like every time I do a search for problems with my car I come up with intelligent information from stangnet, so here I am!

I bought my car as a total basket case. I don't know what I was thinking... I sold my mint '03 GT convertible because I wanted another foxbody, and I went and bought this turd.

Anywho... I took it to the body shop to get the front end straightened out on the frame rack (I told you it it was a turd!) Ran decently when I took it there, went to pick it up and it WOULD NOT start. I messed with it for a good while and figured out that if the MAF was unplugged or plugged in and out of the air flow stream it would start and run. Poorly, but it would start and run... I replaced the MAF sensor and it ran FANTASTICALLY! for about 15 minutes... Then it died while sitting at a red light and wouldn't start for ANYTHING. Left it sit overnight, and when I came back it magically started right up and made it home just fine, but still running crappy. The next day I did a tuneup on it... still running crappy and while I was doing a KOER test, it died. No start again. At this point, I pulled the ECU and replaced all 3 leaky capacitors, and found that fuel pressure was waaaaay low. Changed the pump, put the ECU back in and blammo! It ran crazy good! Pulled hard and smooth right up to 6k RPM! The next day I decided to pull the upper intake, replace some broken vacuum lines, and the PCV valve/grommet/screen and scrape off the layers of grease coating the lower intake. Also, I replaced the thermostat, flushed the rust out of the block, and rplaced the leaky radiator. I didn't have any coolant or distilled water, so I started it up for about 2 minutes to move it off to the side of the driveway and it seemed to run fine.

Next day, I bought some coolant and water and went to fill it up... I started it up and it refused to idle. It ran like poo while I filled the radiator and them when I took it around the block it ran like even smellier poo. Pop burbleburble POP POP bluuuuuuuhhhhhhh POP! Zero power, popping through the intake, etc. Seemed to improve slightly when I unplugged the MAF.

I seriously doubt it could be timing... the distributor doesn't just rotate itself and then rotate back for a couple days... It seems to be an intermittent problem.

I've replaced:
MAF
TPS
Plugs/cap/rotor
Capacitors in ECU
Fuel pump (Walbro 255)
Cleaned/spread ten pin connectors

Things I think it could be:
Plug wires severely arcing
TFI module
PIP sensor
Faulty ECU
Another faulty MAF sensor

If needed I can try to upload a video to youtube of how craptacular it runs...

Any ideas?

 

[tsc]

I should also mention that it bucks like a paint shaker at almost any throttle setting. Also, I pulled the vacuum line to the FPR and there was no fuel getting past the diaphragm.

 

[jcgafford]

pull the codes

 

[mikestang63]

check the vacuum fittings or for a leaky intake gasket

 

[jrichker]

Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

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.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

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

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Equus - Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

 

[tsc]

The only code I could get KOEO was for the EVAP purge valve...

KOER Codes are as follows:
12-RPM at idle out of range/high (duh... got to crank the idle screw in in order for it to keep barely sputtering along)
41-HEGO sensor voltage low/system lean
91-ditto 41
18-SPOUT circuit open or Spark Angle Word (SAW) circuit failure (???)
13-RPM at idle out of range/low

Codes 41 and 91 tell me I have a vacuum leak or yet another failing fuel pump... My POS fuel pressure gauge refuses to read anything other than "0" when I hook it up to the rail ($117 well spent...) and while it was running I sprayed some carb cleaner around all of the mating surfaces of the upper and lower intake, the throttle body and any exposed vacuum lines I could see... I got nothing from that. I messed with the timing a bit and got it to stay alive a bit better and it'll mostly drive down the road, but there's zero power. I didn't even dig out my timing light to re-set it.

The 18 and 13 could be explained by the fact that the engine died right at the beginning of the test every $%#@ing time I tried it. Though I've never heard of a SAW circuit before. The SPOUT connector was in for the test.

 

[tsc]

TTT
Anyone know what a "SAW circuit" is?

 

[jrichker]

Code 18 - SPOUT out or wiring fault - look for short to ground in SPOUT wiring going
back to the computer. Possible bad TFI or defective 22 K resistor in the IDM wiring

This code can disable spark advance and reduce power and fuel economy.

Remove the passenger side kick panel and disconnect the computer connector.
There is a 10 MM bolt that holds it in place.
Disconnect the TFI module connector from the TFI and the measure the resistance between the yellow/lt green wire and ground.
You should see greater than 100 K (100000) ohms.
Check the resistance from Pin 4 on the computer connector (dark green/yellow) and the dark green/yellow wire on the TFI connector. You should see 20-24 K Ohms (20,000-24,0000 ohms). The resistor is located in the wiring harness about 6” from the connector. You will need solder and heat shrink to replace the resistor if it is bad.
Next measure the resistance between the yellow/lt green wire on the TFI module connector and
Pin 36 on the computer connector. With the SPOUT plug in place, you should see less than 2 ohms.

The following is a view from the computer side of the computer connector.

This diagram is the wire side of the computer connector.

Diagram courtesy of Tmoss & Stang&2birds

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

Revised 06-Sep-2012 remove smog pump crossover tube reference

Code 41 is a RH side sensor,
Code 91 is the LH side sensor.

Code 172 is the RH side sensor
Code 176 is the LH side sensor

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 sensor circuit. 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.

Backside view of the computer wiring connector:

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 (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. 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 (LH O2 with a Gray/Lt blue wire) and 43 (RH 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.


Testing the O2 sensors 94-95 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. 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 Os sensor harness and the Dark Green/Pink wire on the computer pin 43

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 Dark Green/Pink Gray/Lt blue wire on the RH Os 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 Os 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

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.

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

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.

 

[FoMoCo17]

Hey man ... you got the same codes I got except the 41 and 18. I got the 12 and 91, 96. I just found a bad TFI module and a bad drivers side HEGO sensor after they reared their ugly heads with no codes. I'm now wondering about the BAP Sensor and am waiting on a meter question response in this forum. Anyway, I didn't see it listed in your possible causes ... but what we are expereincing, the symptoms seem to parallel a bad MAP/BP sensor ... just wanted to throw that out there. I would like to verify mine before replacing because I have thrown too much money at this damn piece of crap. Its amazing Ford would put such an anemic troubleshooting system on a car and sell it to the public ... but then again look how many MS updates I constantly get for my personal PC just crazy!

 

[tsc]

I've got no complaints about EEC-IV, really... I've owned a '91 and '92 F-150, 2 '88 Crown Vics, An '89 Crown Vic, two '88 Mustang GTs, and worked on countless others. All the 5.0 SEFI EEC-IV cars I've owned have been the most reliable and easiest to work on out of the 50+ cars I've owned. This is just the first one that has really made me rip my hair out and want to light it on fire. Hell, I think that given the fact that EEC-IV is damn-near 30 years old, the technology it encompasses is incredible!

New developments:
I removed the valve core from my fuel rail and ripped the core out of the Ford fuel rail adapter on my tester- lo and behold, it WORKS!

Results:
Jumpering the fuel pump test wire to ground gets a split-second spike to almost 20 psi and then it settles to about 15 psi. As fast as you can remove the power from the pump, the pressure bleeds down.

Now, the pump *sounds* like it's pumping its little heart out, and I just replaced this pump last weekend. It's a brand new Walbro pump, and the POS Airtex I replaced was running fine but not building any pressure.

Is it possible that my FPR is just stuck in a full bypass mode? It seems more possible that it was intermittently getting stuck in this mode and that the stock replacement fuel pump couldn't make it run in full bypass, but the Walbro 255 is capable of giving it just enough pressure to barely run in this condition than 2 fuel pumps completely poo'd the bed in the course of 1 week on a car that doesn't even get driven!

 

[jrichker]

Fuel pump pressure test
Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line coming from the regulator. Stick a bolt in the other end of the hose and make sure that all your connections are tight and leak proof as possible. When this powers up, you don't want fuel squirting everywhere. Hook up the fuel pressure test gauge. Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the ECC
test connector and jump the connector in the Upper RH corner to ground.

Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump
If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad. If the fuel pressure does not hit 55 PSI or more in a few seconds, the pump is bad or you have electrical problems.