91 Corolla, bad gas mileage

[K Lea's ol Corolla]

Hello, its the Wife's car, her name's the sig. All the better to get it running good ehh?

We have a 91 Corolla with the 4AFE motor. The car has about 247,000 kilometer on it, and I put a used engine in it 2 years ago March.

I remember after we put that motor in, it ran like a beauty, silky smooth compared to most other 4 bangers we've driven. The mileage was 430 km a tank, mixed city and highway. Most trips it got 480 km to 500 km a tank.

Then, one day, the diagnostic connector fell off the fender, and into the driveaxle area, and got wrapped up a bit. I did not notice for quite a while as I was swapping a distributor out, thinking it had died. It wasn't until then, I realized the connector was the problem.

Ever since then, the check engine light as always been on, with codes 25 and 26. Engine running too lean, and engine running too rich. gas mileage at 350 a tank. No idea what to make of those codes. I repaired the ruined wiring at the connector, and replaced the o2 sensor with a NGK oe fit, and the car got worse mileage. Now I'm only getting 200 km a tank.

Any way to connect a scantool to these cars? I'm familiar with diagnostics of most cars, but this is older technology that i've never had much experience with.

Its had plugs, wires, cap and rotor, o2 sensor, air filter, fuel filter and lines, alternator, battery, starter, complete exhaust, brakes, rear shocks, 2 front fenders, left rear fender, and perhaps more.

Thanks for the help!

[REN69]

As far as I know, these are jumper style, you have to jump the connectors in the engine compartment to get the CEL codes to read.

Have you checked the catalytic converter? this could be the problem as well... either that or you need a new EGR valve.

[wernettejr]

Check out your MAP sensor. It controls how lean or rich the fuel mix is. Usually if it is going bad it will cause it to run rough. If you search you will find instructions on how to test it. Good luck and hope it helps.

[K Lea's ol Corolla]

The car has complete exhaust, including the converter. Old one rotted out. Definitly not a plugged converter, car has all the power you need, and the motor runs silky smooth like new.

No EGR on this one, maybe Canadian certifications were different up here a long time ago. My other car a Park Avenue had none for 2 model years at one time, lol.

Haven't ruled out the MAF sensor, yet.

I think this is related to what happened when the connector wrapped itself around the axle. When testing the o2 wires, i am finding a dead short to ground. O2 works using a multimeter set to millivolts, but at the OX wire to the pcm, there is no signal, and the wire is shorted to ground. Going to Dad's now to stick in a new wire and see what happens. I have to do something, with gas going up every week, I just can't afford to be good friends with the gas stations at 200 kilometers a tank.


Also, looking at wiring, are these fuel injectors batch fired? All the injectors share a same driver circuit to the PCM according to wiring diagrams. I am just used to looking at individual circuits you see in modern cars.

Will keep posting!

[90 GP]

Here's a link on how to retrieve codes without scan tool. Check the vac line leading to MAP sensor for leaks. Has the thermostat been replaced lately? If not will keep it in the cold engine mode longer. Also when engine is cold thee is a vac bleed that elevates idle till warmed up. Remove rubber air intake at throttle body and look for a large square port on bottom ahead of throttle plate. Spray throttle body cleaner in the port as it can stick. You can test it by starting and put finger over port and with cold engine should feel suction. Once engine is warmed up should feel none.

http://www.troublecodes.net/Toyota/

[K Lea's ol Corolla]

I have no problems with getting codes, its TE1 and E1 I believe on the diagnosis connector. The codes were still 25 and 26.

Yup, new t-stat as well. I cleaned out the TB pretty thoroughly last time, so I think its ok.

After I spent time at Dad's, I traced the problem down to a dead short to ground in the wire that connects the o2 sensor to the PCM. This might be related to the diagnostic connector incident we had a long time ago. I was not able to find the short as that will be a weekend project, that is also going to involve taping and covering up some other exposed wires that i've found here and there.

I instead ran a jumper wire, o2 right to the pcm. When I backed the car out of the garage, the check engine light went out!!

Its possible that both lean and rich codes were present because since the PCM could only see 0 millivolts from the o2 sensor, it would compensate by running the engine in an open loop condition where it enrichens the air/fuel mixture.

Time will tell, here is to praying that I get my 500 kms a tank again!