[89Camry89]

I found several topics in the forum with similar symptoms, but did not find clear resolutions.

1993 Camry XLE 4-cyl automatic is gradually getting worse about missing out. It doesn't do it when the engine is cold, so maybe it happens only in closed loop?

It hesitates, or misses out and appears to be associated with a certain amount of vacuum. It's the amount of vacuum when accelerating (gently) from a stop in first gear, or turning (gently) after a stoplight. It's the amount of vacuum on cruise control going up a long gradual incline.

I have learned if I avoid that range of "pull" the engine is fine.

When it happens, it feels the same as an engine missing one cylinder. It's the kind of barely-accelerate lag you would expect if a spark plug cable came loose.

I have some spare parts lying about. I swapped the throttle position sensor and manifold pressure sensor. There was no change. It continues if the oxygen sensor is disconnected. I swapped the entire distributor body and rotor and cap.

Do you have any hints? I don't know if it is a metering problem or something else.

It seems perfectly fine as long as I keep the throttle outside of that range of vacuum. The sputter was hardly noticeable at first and is now lasting for more seconds. First occurence was 2-3 months ago.

Thank you.

 

[Stillrunning]

Test fuel pressure.

 

[89Camry89]

Test fuel pressure.

I finally got some readings. I removed the banjo bolt from the top of the fuel filter, attached a pressure transducer there, and then drove around normally. (I did not jumper any of the wires of the check connector.)

The lowest fuel pressure observed overall was 35 psi (lower RPMs).
The highest fuel pressure observed overall was about 46 psi (higher RPMs).

Once again, when the engine is warm, the sputtering occurs at ~2000 RPMs and 45 psi fuel pressure.

The problem is observed on occasion from 1900 to 2200 RPMs. In each case, the fuel pressure was 45 or 46 psi.

At RPMs above 2200 the sputtering does not occur even with the pressure at the max observed levels.

This seems to be just outside of the numbers I see in the service manual (44 psi).

Do these observations suggest fuel pressure as the culprit?

Many thanks for your time and knowledge.

 

[Stillrunning]

Nice setup. I don't think those psi numbers show any real problem. The fuel pressure should remain constant as the pump is electric and not tied to the rpm. As you observed the pressure does not relate to the sputtering.

So now you know something, and you'll need to continue to trace the cause. Right now I have no suggestions.

 

[94Camry 2Door]

Suggest opening up your distributor and look at the coil and condenser. These old OE internal coils are stupid durable and can continue to work even when cracked and burnt. The condenser over time/age will melt out and can start to short to ground. Look for heat fractures in the coil and the clear resin that seals the internal coil wiring at the high tension lead. It's the part the spring loaded button in your distributor cap contacts the coil to transfer the high voltage spark.

 

[89Camry89]

Follow-up. The problem ended up being the spark plug wires. There were no outward signs of arc to ground, no wear in the insulation, and no other reasons that would have led me to suspect the wires were the problem, other than moving on to the next thing.

I switched out the wires and the trouble was immediately gone. I drove it around for a few more days to be sure. Now it's parked until I sell it.

In retrospect, perhaps I should have thought of it earlier. Several years back I'd had a loss of one cylinder in my 1989 Camry. It would come and go. In that case it was a plug wire grounding out somewhere along the valve cover and when I caught it in the act, I could see or hear it happening.

For the 1993, however, there was no external detectable sign, and I didn't suspect the wires because the problem existed in such a narrow set of conditions. I am still at a loss to fully explain the science of why it failed in this exact manner.

Lesson learned; when it doubt, try spark plug wires.