1993 Toyota Tercel 1993 Toyota Tercel DX misfiring at all s

Tiny
BRUNCIAK
  • MEMBER
  • 1993 TOYOTA TERCEL
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 16,500 MILES
There is a misfire at idle and all driving speeds. I performed a major tune-up, found and repaired exhaust leak at flange between manifold and O2 sensor. I checked for DTC's, none found. Idle, timing, fuel pressure are all in spec. Injectors are operating. Air flow to the engine is fine. Checked vacuum. 20-21"Hg. Vacuum acts normally when revving engine. The car has no EGR valve or MAF. Tested ignition system. Ignition and Pick-up Coil specs are OK. Air gaps in distributor are in spec. I replaced the ignition module(ignitor) with no change. The car runs better at higher rpm's but does have slight hesitation getting up to speed. Cruising at 55mph a misfire is noticed every few seconds. I did not perform a compression test since the vacuum test passed.
Wednesday, December 31st, 2008 AT 3:47 AM

3 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Hi brunciak,

Thank you for the donation.

You did not mention if you checked the spark plugs or ohmed the spark plug cables.

Did you check the valve clearances?
Any restriction in exhaust system?

Apart from above, you seem to have covered everything that might possibly cause backfiring and hesitation.

Happy New Year.
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Wednesday, December 31st, 2008 AT 7:10 AM
Tiny
BRUNCIAK
  • MEMBER
  • 3 POSTS
Thank you for the prompt reply. I removed all the spark plugs and saw no fouling. I am getting spark at each wire with a tester. I did not check valve clearances. I don't think there is any exhaust restriction since the car has no problems with wide open throttle. I will check the valve clearances as soon as I can though.
Is there any chance the O2 sensor could be damaged and giving the computer a wrong signal without a check engine light. The exhaust gasket was damaged for quite some time(possibly a year) and the last time this condition(misfire) occurred the #1 Spark plug ceramic surrounding the center electrode was split so I did the major tune up. Now the same misfire is back( 3 Months later), but nothing is damaged. This time I noticed the exhaust leak and repaired it. That's why I'm wondering if the O2 sensor is giving false signals and if it would cause a misfire. Also it is a random misfire.
Thanks again.
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Thursday, January 1st, 2009 AT 11:00 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Hi brunciak,

Yes, an O2 sensor operating out of specs can cause the fault and it might not show on the CEL. Only a data diagnostic would be able to tell if it is faulty.

You did not reply if you tested the resistance of the spark plug wires. All should have resistance and below 25 k ohms.
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Thursday, January 1st, 2009 AT 3:20 PM

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