1993 Camry 4 cylinder Losing Power Under Load

[Brian R.]

I would replace the MAP sensor. Do the compression test anyway. It's useful information on the general condition of the engine. Check the fuel pressure and flow rate. It's not likely the problem, but it's difficult to make judgements over the internet. Have you spent some time examining the vacuum hoses? The engine is pretty old to have the original vacuum hoses without at least one bad hose or connection.

[frafreg]

I have inspected the vacuum hoses as closely as possible. I even removed a few that I thought were suspect.

Without any error codes I don't have any direction. I'm going around in circles. Before I check fuel pressure, I want to try to use the E1 to TE2 level of diagnostics which I understand is more sensitive. The service manual says I can test drive the car and then, jumper TE1 to E1 to see any additional error codes. Have you done this level of diagnostics before? Thank you.

[frafreg]

I checked fuel pressure, and all was good. I decided to go back and check my spark plugs and wires again. I tested them previously with my meter and the resistance was good on all four wires. Today, using a spark tester, I checked the spark on all 4 plugs and they were all good. Then, I noticed at the bottom area of the spark plug connector, there was a very small gray spot on the side. With the spark plug tester on the spark plug and the boot outside the hole, I noticed it sparked to the valve cover from this very tiny gray spot. I checked the other wires and they all had the same little gray spot in the same spot. They were all arcing inside the hole. This not something you can see unless you extend the boot outside the hole. I put in an old set of wires and it fixed the problem.
These are Duralast wires which I purchased from Autozone. They all failed the same way at the same time. I think it’s a defect in the hard-plastic mold. I won’t ever use Duralast again. I saw a set of NGK wires which look pretty good for about $40. Do you have any suggestions about a good set of aftermarket wires comparable to the original wires or should I go to Toyota? Thank you.

[Brian R.]

NGK wires are top notch. Use them.
http://www.automotiveforums.com/vbul...2&postcount=15

https://www.amazon.com/NGK-TE43-Prem...toyota%3Acamry

https://www.amazon.com/NGK-Iridium-S...toyota%3Acamry

[frafreg]

The first thing I did to diagnose this problem was to check the wires, plugs, distributor cap and rotor with my meter and they all checked good. There was never any indication of a misfire while watching the plugs fire with my tester. I ordered a new set of NGK wires, but I am considering removing the Bosch plugs and replacing them with NGK or Denso plugs. I want to run the car for a while to see how it performs long term and then decide.
Another mystery I have not been able to account for is why the misfire went away under a load when I advanced the timing. If the wires are arcing, they should always arc. Also, why did the idle get steady when I removed the vacuum hose from the fuel pressure regulator? There is still a misfire right?
This has been a great learning experience. I enjoyed learning about stoichiometry and how the ECU maintains the 14.7:1 air / fuel ratio based on all the sensors. Unfortunately, this ECU doesn’t report a misfire. The misfire was quite severe under a load and this should have been enough to trigger some kind of a code.
Another observation was that I never got an oxygen sensor error code even when disconnecting the O2 sensor. Probably because it isn’t a heated sensor. It has one wire and from what I understand, the O2 only works after it reaches about 600 to 700 degrees. I see the short-term fuel trim change when accelerating which means the ECU must be using that data. From what I read in the service manual, the ECU can detect open or shorted sensors, but I don’t think it will detect a sensor that is out of specification. The ECU also doesn’t report code 24, IAT sensor. The sensor has voltage going to it and the IAT sensor tested good. I was told that the IAT was not part of OBD1. However, just because it doesn't report the error it may still use the sensor input. Thanks again for you help! I appreciate it.

[Brian R.]

Thank you for the feedback.