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Old 12-29-2015, 03:43 PM   #1
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Miss fire issue

I have an '88 with a stock 5.0 motor and my problem is that every morning
When I fire up it has missfire and run awful until reach normal temp,that was in the beginning. Now are doing it at cold or normal temp but when the missfire is gone and that's about 10 minutes after I start the engine I have lost of power. I scanned have no codes,check fuel pressure and flow and it's normal,the ignition system and spark plugs are ok also fuel injectors. I was thinking that could be pcm issue but not so sure. If anyone can help me with some advice I will appreciate.


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Old 12-29-2015, 04:54 PM   #2
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How old are the Spark plug wires, and have you checked the timing and would also check the compression!
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Old 12-29-2015, 05:08 PM   #3
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Are you getting no codes period or are you getting code "11" system pass code but no other codes??You definitely need to do the salt & pepper shakers maintenance listed in the link below.Weird driveability issues will occur if these connectors are loose or corroded.You also need to check for vacuum leaks by using carb cleaner or propane but be careful & have a fire extinguisher nearby.A vacuum leak causes the o2 sensor to read lean.
A defective ect sensor sounds like the most likely cause though.Test it while the engine is cold,then start the car & let it reach operating temp then test it again.You wanna get a cold reading & hot reading then compare the readings to the chart shown below.If the numbers don't match,the sensor is bad.To test the sensor,disconnect the wiring harness,connect a (+)ohmmeter probe to one of the ect sensor terminals & connect the (-)probe to the other terminal.

Salt & Pepper (10-pin) Connectors Fix
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Old 12-30-2015, 05:56 AM   #4
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Yes I getting code 11 "system pass". It is possible that if the coolant temperature sensor and o2 sensors are faulty but the pcm don't set a code for it?


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Old 12-30-2015, 11:28 AM   #5
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They should throw codes most of the time,but they might not if the sensor is on the very edge of passing/failing.Example:you could have a o2 sensor that's operating,but operating slowly so it wont set a code.This is called a lazy sensor.The link below will help you test the o2 sensors.
Have you checked the spark plug wires??Let the engine idle,individually disconnect each plug wire & listen for the idle to change.If it doesn't run any different with the plug wire disconnected,that plug wire is bad,that plug wires contact on the distributer cap is bad or that injector might not be firing.A compression test can locate a suspect cylinder if its reading is much lower than the remaining cylinders.
A vacuum leak can cause misfires,but it also causes the o2 sensor(s)to read lean normally,but if the leak is really small it might not cause a lean o2 signal.
I would also check the egr valve to make sure its not sticking open.It should only be open during part throttle (cruise)conditions. When the egr valve is open,the ecm leans the fuel mixture & advances timing,which is just the opposite of what the engine needs at startup & during warmup.The ecm will delete egr function in the logic,if you remove the vacuum hose from the valve.That means,fuel & timing settings will go back to normal,so do this.Remove the vacuum hose from the egr valve, plug the hose then take the car for a test drive.If the misfiring & rough running conditions go away,the egr valve is dirty & stuck open,egr valve is defective or the evr solenoid on the strut tower is defective.
If the misfiring & rough running condition occurs on a constant basis instead of being a intermittent type issue,you might wanna check the fuel pressure to rule the fuel system out as a possible cause.Fuel pressure should be 35-45psi koeo & 30-40psi koer.Check for bleeddown pressure too.Turn the koeo & take a pressure reading,turn the key off,wait 60 seconds then take another reading. Pressure should not drop more than 5psi,from the koeo reading,in that 60 second time period.If it does,an injector is leaking,the fuel pump check valve is bad or the fuel pressure regulator is leaking/stuck open.To test the regulator, let the engine idle,pull the vacuum hose off the regulator.Do you see/smell fuel inside of the vacuum hose or do you see fuel seeping from the regulator vacuum port??If the answer is yes,the regulator is bad.Its also important to check this hose for a vacuum leak too.If the regulator is leaking fuel past the diaphram or its sticking open & sending fuel back out the return line to the tank,adequate fuel pressure won't be maintained & that will cause misfiring & sputtering.Another thing that happens with a leaking fpr is,fuel(from the leaking diaphram) gets drawn in through the vacuum hose and makes its way into the intake,then makes its way into the exhaust triggering the o2 sensors to read rich.If the o2's read rich,the ecm will then reduce the fuel mixture in an attempt to get the Afr back to normal,but it reduced the fuel mixture falsely because it really wasn't rich to begin with,the leaking fpr just made it appear that way to the o2's & ecm.The o2 sensors read oxygen not fuel,so if there's too much oxygen(due to a vacuum leak) in the exhaust,the o2's will read lean & if there's too little oxygen(due to a leaking fpr) in the exhaust,the o2's will read rich.

(O2 Sensor Testing Link)
O2 Sensor Codes 41/42/91/92 Troubleshooting
(ECT Testing Link)
ECT Codes 21/51/61 Troubleshooting[COLOR="Silver"]
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Old 12-30-2015, 05:28 PM   #6
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Thanks for the advice. I will check all that and let you know what I find.


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Old 01-16-2016, 06:01 AM   #7
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Well I did all what you told me and I found a bad O2 sensor. But when I plug the battery back I start the engine and let it idle until reach operating temperature when I shut off and started again the RPM gets up and down until get stable and when I hit the gas it's dose nothing like choke and then when revs up its detonate from the air cleaner like being wrong timing set but is not and only happens when I shut off the engine and started again.
Also I check the TPS reading and reeds.998 but that reading began to drop voltage. I replaced the TPS thinking that was the problem but the new one does the same.


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Old 01-16-2016, 07:00 AM   #8
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Also has a strong emissions smell from the tailpipes


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Old 03-05-2016, 05:08 PM   #9
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Well I change the pcm and the fuel injectors were leaking fuel, so I replaced the injectors for new ones and I fix the problem. But, now the engine idle at 1100 rpm then 800rpm and go back to 1100rpm. When I step in the clutch when I shift gears the rpm go up by itself. I scanned and set code 63 (tps below voltage) I set the tps voltage to
.999 at close throttle I start the engine and works fine until I depress the throttle then start to do the rpm problem again and when I scanned set the same code 63 again. The tps sensor is new from auto zone and I replaced like three times and it does the same problem. If anyone can help me with this I appreciate because this problem is making me crazy and I don't know what else to do.


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Old 03-10-2016, 09:47 AM   #10
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I would remove the IAC valve & clean it with carb cleaner,dry it thoroughly,reinstall it and do a base idle reset following the link instructions.
Test the TPS wiring too and check the TPS pinouts at the salt & pepper connecters.
If the vehicle is in motion and slowing down to a stop,the engine is supposed to idle up a little when you push the clutch pedal down & when you're shifting gears.That's called the idle dashpot strategy.You might wanna check the inside of the throttle body too & clean it if its got carbon buildup on it.That can cause the throttle plate to hangup.
After you do the base idle reset,drive the car for 15-20 minutes so the ecm can relearn its adaptive correction factors & idle strategy.You might/might not experience driveability issues during this time.
(TPS)
TPS Codes 23/53/63 Troubleshooting
(Base Idle Reset)
Summarized/Corrected Base Idle Reset Procedure

---------- Post added at 09:47 AM ---------- Previous post was at 09:47 AM ----------

I would remove the IAC valve & clean it with carb cleaner,dry it thoroughly,reinstall it and do a base idle reset following the link instructions.
Test the TPS wiring too and check the TPS pinouts at the salt & pepper connecters.
If the vehicle is in motion and slowing down to a stop,the engine is supposed to idle up a little when you push the clutch pedal down & when you're shifting gears.That's called the idle dashpot strategy.You might wanna check the inside of the throttle body too & clean it if its got carbon buildup on it.That can cause the throttle plate to hangup.
After you do the base idle reset,drive the car for 15-20 minutes so the ecm can relearn its adaptive correction factors & idle strategy.You might/might not experience driveability issues during this time.
(TPS)
TPS Codes 23/53/63 Troubleshooting
(Base Idle Reset)
Summarized/Corrected Base Idle Reset Procedure
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