My husband bought a 03 blazer fairly low miles drove for 2 years no issues just regular maintenance. Started to miss off and on slightly. Then one day it just quit. When started would idle very rough! Replaced spider fuel injection, fuel pump, fuel filter, spark plugs, wires, mechanic replaced all these things he keeps trying all the sensor switching out and returning as it doesn’t fix the issue. Called last week said it would run perfect for a couple of minutes then goes all to pieces and runs worse then before. Anyone have any idea at all? Thanks

 

1. Any codes?
2. Need to do the 10 min fuel pressure leak down test
3. Need to look at fuel pressure and spark when it runs like crap
4. Next would be sensor values and live data like fuel trims and O2 sensors
5. May need a compression test

George

 

sounds like a failed computer assuming all else is good original parts.

 

Yes but I would perform a compression check and check for a a leaky manifold. Mine had the same problem but it was the spider.

 

time for a COMPETENT mechanic , yours isnt. Hes guessing and its illegal to blindly throw parts in it and charge you for them if they werent defective. This is typical for persons who dont understand overall engine systems and just grab at straws to guess at throwing parts around based on computer codes

Theres a " divide and conquer" strategy here and more blind guessing with computer codes wont work.

Each cylinder must have "AFI" , air, fuel and ignition, and no excess oil.

Must analyze at the spark plugs, Oxygen Sensor and exhaust tips.

The MOST important step is remove all the plugs and see if all and how they are rich. Could be fuel or oil fouling from bad piston rings or leaky valve guide seals. A compression LEAKDOWN test will reveal leaky or broken piston rings. A simple quick comp test isnt good enough.

This is a computerized engine with Oxygen Sensor, if it fouls even temporarily from a cylinder too rich or oil the computer cannot sense mixture and adjust. A significant over- rich at any time can destroy the sensor by covering the sensor element with fuel/ oil / carbon deposits. Remove it, its probably fouled. If so it must be replaced, Im not sure it can be cleaned. Even residual trash that remains in the exhaust system from being too rich can damage a new sensor. If its light fouling that hasnt had enough exhaust heat to bake on, solvent spray might clean it, or just finish it off.

If the engine has dual exhaust, swipe a finger inside each tailpipe outlet to see if theres lots of black fluffy deposits. If both are contaminated, on just one, that proves its a problem with some or all cylinders on one or both banks of the engine.

An over rich condition is from excess fuel or WEAK IGNITION, rarely from insufficient air. Ignition fools mechanics as they never learn anything useful about electricity or electronics. Theres a chronic problem in old vehicles with bad wiring that prevents the ignition system from getting enough voltage to operate properly.

The weak link is the Oxygen Sensor, for a gross fouling problem, it can be contaminated or damaged very quickly, minutes, not hours. May have to replace it and limit engine testing to cold start and idle or low RPMs to have a chance for the sensor to live long enough to operate. That point is usually engine water temps about 140* F. The engine ( computer) must operate Open Loop up to that temp and does so without O2S input. Thats where gross fuel problems are detected.

Start with checking all spark plugs, theyre probably black. Install new ones, put a timing light on the coil wire and start the engine. Check fuel pressure. The timing light will indicate firing of all cylinders, it may be missing. Arc a spark to the engne block or spark plug tip in low light conditions, the spark must be white, not dull orange. Check DC voltage at the distributor, it must be at least 14 volts running, 13 or less the spark goes toward weak orange and that will mimmick an over rich condition where the fuel is otherwise OK. Thats
" misfire" and itll kill an O2S very quickly.

If the timing light flashes steady, almost continually, and spark is white) blue with all new spark plugs, its a fuel problem.

An over rich appearance is also caused by a too LEAN mixture as the spark plugs must have sufficient fuel in the gap to fire under pressure, if not, the pkug doesnt fire and that fuel which does not burn makes the cylinder too rich.

Oil is considered fuel also, just extremely dense fuel that fouls spark plugs and O2Ses, check a new or cleaned O2S after warming up to maybe 100 degrees to " read" the outer shell to see if it has gas or oil on it. It can be " read" like a spark plug to determine rich, lean or fouled exhaust.

Bad valve guide seals will directly put oil in the cylinders and cause spark plug fouling, remove new clean spark plugs after a few minutes and see if they are coated with oil.

Leaking INTAKE seals load the cylinders with oil, EXHAUST seals dump oil into the exhaust manifolds and contaminate the O2S, the difference is that oil into the cylinders is exposed to combustion so it gets " burned", the difference shows up on the O2S as partially burned black deposits or raw oil.

Also beware of an O2S thats not " grounded " to the electrical system, thats a surface catalyst with a resistance on the order of megohms, a very low current source that may be on the order of 0.8 Volts, ( + or - tenths) measure the O2S signal line with a DC voltmeter. The O2S grounds thru the exhaust system manifold bolts back to the engine block. There must be a ground wire from engine block to chassis in common with the computer and sensors.

That should narrow the problem down.

Clean newer spark plugs which have been fouled with Muriatic acid. Theyll come clean like new.

 

ps if its rich and not setting an O2 code the sensors probably bad. Also when installing new spark plugs and O2S to " start over" also disconnect the battery for 5 minutes then reconnect to clear the PCM memory - it may have learned bad data.