EEC-IV masters, please help.

[93rev2sev]

Please read this for background:
http://www.shoforum.com/showthread.php?t=72616

I have new information...

My GF has had the car for a while and it dosent bother her, so it has not been high on my priority list. I swapped plugs & wires but thats it. Hopefully with the info I give you below, you can tell me what I need so I don't have to waste money hanging parts on it. I obviously can't read codes for anything, so I am relying your better than average understanding of the EEC-IV system. I had the car all week so I took that as an opportunity to do some "field testing".

After putting a few hundred miles on it, I started noticing some patterns in the powercurve. As an experiment, I swept up the RPM range in all gears very slowly so that I could listen to the engine at all speeds. It turns out there is a noticable surge in power at all RPM ranges that is not felt under "normal" driving. At higher RPMs(3000+), while at a constant speed in first and second gear, I can feel the car surge. The computer/sensor system is obviously causing this (AKA not plugs, wires, injectors, coil). The (approximately) 1 second power surges happen at regular intervals spaced about 1.5 seconds apart...like (computer) clockwork.

Now I know most people will tell me to change O2 sensors, MAF sensors, etc..

I was hoping someone very knowledgable in the EEC-IV could chime in with exactly what is happening. I would not be surprised if the information above is enough for someone to diagnose EXACTLY what sensor is wonky and how the computer is reacting (based on the timing of the surges? I can be more precise if needed). I know a thing or 2 about computers in general so don't be afraid to get a little bit technical.

 

[Mr Anonymous]

The surging sounds symptomatic of a sticking IAC valve -- the PCM is trying to get the right amount of air flowing through it, and it's having to force the solenoid too far in both directions to get past the sticking point(s).

It's probably completely unrelated to your perceived lack of power in the other thread.

WRT to that thread, presuming all the maintenance items you mentioned were done properly and the car is in overall good working order and there are no DTC's pointing at an issue, realistically you need to get the car on a dyno to check the power and torque curves along with the A/F to see if anything looks unusual. It might just be a slow car. Some cars are just slow. Don't forget that the '93 probably weighs a hundred or so pounds more than the '90 so that's also going to make it a bit slower simply as a function of physics.

 

[93rev2sev]

It idles perfectly stable. Does not surge if I idle up the diveway(it compensates for the load of the slight incline). Only under part throttle. It definately feels like something switching on and off. Would the aic be a factor under part throttle? I'll have to see if it happens under WOT. But I'm pretty sure that's my power loss.

 

[armerdan]

I know this sounds stupid, but is your A/C on?

 

[93rev2sev]

I know this sounds stupid, but is your A/C on?

Thats not stupid. It feels just like that; like the A/C is cycling.

The shortened belt bypasses the A/C Compressor. There is no A/C.

I drove it in to work this morning...same thing. Only happens once the car is warmed up. It's more like a half second of power and about 1 second between surges. It is consistant accross the RPM band. It happens with the secondaries open or closed. Light throttle or WOT. I can record the sound of the engine at 5k RPM in first so you can hear it. Just not immediately...stay tuned.

 

[93rev2sev]

OK, it happened again on the ride in to work this morning but not on the way home. It felt more powerful on the way home too.

 

[1slickRED89]

Have we meet at any of the dearborn lunches? i'm terrible with screen names.

anyway, as a last resort, and if all else fails, and since I in dearborn all the time for work. I have a break-out-box and a handheld O-scope so I can see all the signals that may be causing a problem, might find something out, let me know.

 

[93rev2sev]

Now were cookin!

You will have a PM sir!

 

[93rev2sev]

The problem is fixed. I have no doubt that I had a bad MAF. Cleaning it didn't help so I swapped it and WOW!

yippie!

 

[93rev2sev]

OK so Maybe NOT fixed!

Car runs very well but this morning I felt that puslating again. I'm starting to think I have an 02 sensor problem. I am going to test them with the procedure on the SHOTIMES.COM site:
http://www.shotimes.com/php-bin/mod...le=article&mode=thread&order=0&thold=0&sid=87

But I have 1 questions...

A. What makes a volt meter a "high impedence" volt meter?
I have a decent electronic volt meter but I don't know what the "high impedence" thing is...

 

[hawkeye18]

Any digital multimeter will work. Analog "sweep" meters are generally not high-Z.

 

[93rev2sev]

Any digital multimeter will work. Analog "sweep" meters are generally not high-Z.

Thanks, I'll post my findings.