slight engine miss, 1st 2nd gear shifts hard

[herbie1974]

I just bought this 95 blazer with 4.3 and it seems to have a slight miss especially over 45mph, i have checked the plugs and wires and all seem fine. the miss is intermitent and only seems to ack up on interstate. also the transmission seems to shift hard from 1st to 2nd and 2nd to 3rd the rpms get up to 2500 before the shift occurs. also if i manualy shift from 1st to 2nd all is smooth, 2nd still runs to 2500rpm shifting manually. Please Help! just changed the fluid and filter last night and nothing changed. also am getting a P0420 code and just found out after many days of research the converter is bad. will this effect this other items and cause the symptoms.

[MT-2500]

Code 420 does not say cat is bad.
Bad Engine miss can set a code a code 420.
Any other codes?
If a engine miss go over secandary ign and check fuel filter and fuel pressure.
When was last tune up?
How miles on ut?
Ac Delco plugs?

[MT-2500]

http://www.troublecodes.net/articles/catfailure/

DTC P0420, P0421, and P0430 & P0431: Check Possible Cause Of Misfire DTC P0420 and P0421 indicate bank one catalyst system efficiency is minimum requirement. DTC P0430 and P0430 indicate bank 2-catalyst system efficiency is minimum requirement. Possible causes are as follows: Use of leaded fuel. Oil contamination. Cylinder misfire. Fuel pressure too high. HO2S sensor improperly connected. Damaged exhaust system component. Faulty ECT sensor. Faulty HO2S. Ensure ignition timing is correct. Retrieve all Continuous Memory DTCs. If misfire code is not present, go to next step. If misfire code is present, isolate cylinder and repair as necessary. Check HO2S Monitor DTCs If DTCs P0136, P0138, P0140, P0141, P0156, P0158, P0160, or P0161 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. Check ECT Sensor DTCs If DTCs P0117, P0118, P0125 or P1117 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. If any codes except P0420, P0421, P0430 and/or P0430 were present in step 1), service as necessary before continuing. If no codes except P0420 and/or P0430 were present in step 1), go to next step. Check Rear HO2S Wiring Harness Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step. Check Fuel Pressure Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC. Check For Exhaust System Leaks If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair or replace as necessary. If exhaust system is okay, go to next step. Check For Exhaust System Restrictions Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step. Check Manifold Vacuum Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11). Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non- restricted system, manifold vacuum should quickly rise to normal range as increased RPM is maintained. On a restricted system, manifold vacuum will slowly rise to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step. Leave tachometer and vacuum gauge connected. Remove exhaust pipe from exhaust manifold. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST. Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test-drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom.

[herbie1974]

I am not sure when the last tune up was, i pulled the plugs and all looked well, still could see the white on the inside around the base. they are a/c delco plugs and i tested the wires and they show anywhere between 2-3ohms. There is 148000 on the vehicle and i noticed the converter is an aftermarket not sure the brand but it is UPSIDE DOWN, the heat shield is facing the ground. The miss is not real harsh or can it be expected to miss at certain times, it is intermitent.

[herbie1974]

one other thing is the o2 sensor behind the cat is reading the say as the one before. there are no other codes. cleared several times and the only one to ever appear is PO420

[MT-2500]

Originally Posted by herbie1974

one other thing is the o2 sensor behind the cat is reading the say as the one before. there are no other codes. cleared several times and the only one to ever appear is PO420

That points to a dead cat. If 02 sensors are reading good?
Are 02 sensors switching good over and under .500 volts.
Go over secandary ign good for the engine miss.

I would replace the plugs and wires and check cap and rotor and dist shaft for side play wear.
What engine code and is computer on fender well or behind glove box?

[herbie1974]

Originally Posted by MT-2500

That points to a dead cat. If 02 sensors are reading good?
Are 02 sensors switching good over and under .500 volts.
Go over secandary ign good for the engine miss.

I would replace the plugs and wires and check cap and rotor and dist shaft for side play wear.
What engine code and is computer on fender well or behind glove box?

There was a new dist installed before i purchased vehicle, computer is on fender, where do i find engine code?

02 sensors read good.

did you notice the post earlier about the condition of the plugs and wires?

would you still replace them?

What is the secondary ignition?

[MT-2500]

Originally Posted by herbie1974

There was a new dist installed before i purchased vehicle, computer is on fender, where do i find engine code?

02 sensors read good.

did you notice the post earlier about the condition of the plugs and wires?

would you still replace them?

What is the secondary ignition?

Secandanry ign = plugs and wires and coil and cap and rotor.
I would replace wires and plugs first thing if missing.
Check for good hot blue spark to all plugs.
Engine code is the 8th vin no.

[herbie1974]

The engine code is W, how is the best way to check the coil?

[herbie1974]

The cap is good, rotor good, it appears it just had a tune up before i bought it. all secondary looks as if just replaced, no wear on any items. Maybe they thougt this would solve the miss. It is very slight, nothing hard, just know its not to be there, wife drives this and need it to be dependable.

[MT-2500]

Originally Posted by herbie1974

The engine code is W, how is the best way to check the coil?

Look for good hot blue spark with a spark tester and always check it after it is good and hot.
Good Luck

[herbie1974]

New symptom, wife was driving to work; vehicle died on interstate without warning, checked for fire and is not getting any fire to plugs. Replaced wires last night with very good premium brand. Anymore thoughts and what would cause this?

[MT-2500]

Originally Posted by herbie1974

New symptom, wife was driving to work; vehicle died on interstate without warning, checked for fire and is not getting any fire to plugs. Replaced wires last night with very good premium brand. Anymore thoughts and what would cause this?

Proper testing.
If no fire to plugs move on to testing for spark from coil.
Good luck

[herbie1974]

coil has spark, rotor turns inside dist. Pick up coil? cam position sensor?

[MT-2500]

Originally Posted by herbie1974

coil has spark, rotor turns inside dist. Pick up coil? cam position sensor?

If coil has good spark and no spark to plugs and dist is turning it is bad coil wire /or plug wires or dist cap and rotor.
Check if coil wire is putting spark to the disrt cap.
If so check for spark out of cap.