1995 Geo Prizm • 185,000 miles

1995 Geo Prizm 1.6 liter Toyota engine.

It has rough idle, No power to accelerate and very slowly under load.
Exhaust manifold gets cherry red hot in under 5 minutes of driving.
One time flashed codes form CEL and had code 25 and 26. Code 25 is run lean, code 26 is run rich. Cleared codes and no new codes have flashed since, we are still having the same problem.

Troubleshooting and Work Done:
- recently replaced valve cover gaskets found that the wires and plugs were poor.
- Replaced plugs, plug wires, Distributor cap, rotor and coil.
- Replaced fuel filter - had 70 psi after new filter before injectors.
- Engine compression is good between 185 and 200 PSI when warm.
Doesn't seem like it has jumped time on the timing belt with having good compression, but I Pulled the valve cover to check marks anyway.
- When I pulled the plugs for the compression test, plugs for cyl 1, 2, 3 were chocolate colored #4 was white, (Lean)
- Pulled the wires from each individual injector, it stalls when #s 1 & 3 were pulled, no change when #s 2 and 4 were pulled.
- Injector supply voltage was good at 13.8 volts. Resistance across injector terminals was consistent at 13 ohms each
- EGR valve clear and operational.
- O2 senors operational, have changing voltages between0.17 mV & 1.0 volts
- Checked for vacuum leaks, none were found, sprayed starting fluid around intake manifold gaskets, (no change in engine rpms)
- checked the ground behind the starter has no resistance between ground wire connector and the engine.
- Catalytic converter is not plugged - I split exhaust pipe at a break in the pipe just after flex connector under the engine run - no change except now its really loud. Replaced broken exhaust pipe, found catalytic converter clear. Found a burnt set of wires behind the engine, above the exhaust that feeds the second O2 sensor.
- Removed bad section of wiring harness, soldered in new wire splices.
- Went to start it and the battery was dead, my son left the key on after pushing it in and out of the garage to work on his car. (Thanks kid)
- charged battery overnight, turned over fine sputtered to life.
- took for a very short test drive, same problem, exhaust still cherry red.

BUT GET THIS: now when I pulled the plugs to have a look at them I found that the lean cylinder problem has moved! Cyliners 1 & 3 are now running lean and cylinders 2 & 4 are very rich, black and sooty.

I'm at wits end with this, it seems to be whatever controls each set of injectors so it cant be the MAP or TP sensors since they make adjustments to all injectors right. I'm baffled and could use a pointer or two, thank you so much in advance for any advice you can provide.

April 29, 2012.

On ECM injectors 1-3 and 2-4 seem to have different ground inputs with which to do injector grounding. Both are located on same spot at back of intake manifold as brown wires 3 wires total on connection.

Apr 29, 2012.
The grounds have been cleaned and checked, no change. Is there a ground under the dash at the ECM? I have only been working under the hood. I didn't see one shown in the service manual, they just mentioned to clean and check ground #106 which is under the intake and tucked in behind the starter motor, had to pull the starter to get to it.
Anyway after all that and still no change, so while it was running I pulled the connector from the map sensor and it stalled, I pulled the connector from the throttle positioning sensor and there was no change whether at idle or during free acceleration (no load). Could it be an TPS malfunction? Is there a test I can perform with a multimeter to check it?
Thanks again

Apr 29, 2012.
Yah you van do an ohms test to watch sweep.

May 2, 2012.