Luis de Prat

I think you should try picking up a decent used DME on Ebay.

My car developed a similar situation after replacing the factory chip with an aftermarket. It would run great until it reached operating temperature and then it would be very erratic.

I replaced the entire DME with a used unit, and everthing was normal again. Keep in mind that these electronics are now 20+ years old and they do heat up every time you run the car.

If it's not the DME it's good to have a spare and they're quite easy to resell if you need to.

75ohm

Luis, I agree...

I am hoping we can check for cold solder joint issues, along with, continuity on some of the connections...

PeteL

Took the car from the shop today and went to Jason's (75 ohm). We swapped AFM. No change.
Swapped DME. No change. (Both off his car that is running well).
We know there is a miss. You can hear it. Our current line of thinking is that it may be mechanical. Our theory is there is a bad cylinder or more correctly a bad valve. So. The next step will be compression check and go forward from there.
This kind of makes sense. Since we have virtually ruled out electronics, fuel, and vacuum. It may also explain why the car appears to be running a bit hot, not by the gages, but by how hot the engine feels after a relatively short drive. Jason drove it, and agress it is not accelerating right.
Although on the way home it felt peppy....grrr...

75ohm

Beers were cold and the company is always good... car looks great man... we'll get it.

peanut

did you remove the plugs and check them ? if you have a lean mix or poor compression in one of the bores it will show on the electrodes. Don't forget to keep them in the right order though

75ohm

Reportedly the plugs were changed and the old ones were fine...

peanut

I wasn't enquiring about the working condition of the spark plugs .


Looking at the colour and deposits on the electrodes is the best diagnostic you can use on a car. It tells you exactly how each cyclinder is performing in relation to all the others

. If you don't know how to 'read' your spark plugs how can you possibly tell how your engine is performing ?

75ohm

Old ones were fine = electrodes were clean... you have to do better than that mate!

Have another pint and relax... we certainly are.

peanut

75ohm

Exactly.

PeteL

So it may be mechanical.....?

PeteL

New plan: Check compression. I am also going to fix oil leak at pan gasket, and rod bearings.
Then with that done, will address the top end of the engine. I am hoping a bad lifter or bad valve spring.
It appears that all sensors are good.

75ohm

When are you doing all this -- as in, what day do I need to take off?

PeteL

I want to do compression sooner than later.
As for the bottom end, not sure. Still prepping for the triathlon, which has precedence for my time. Perhaps early August for that.

PeteL

Almost a year later, some progress, more confusion.
Status - Had the oil pan gasket replaced, to stop a pretty big oil leak.
While there, the mech noticed the low/no power situation. He cleaned and adjusted the AFM and the problem improved.
When cold (morning drive to work of 36 miles) the car runs great. Good pull from a stop accelerates in all gears. In fifth it will accelerate from 70 mph...
In the afternoon/evening with ambient temps in the mid 90's, the car is a whole different animal. Have to rev high to get it moving, just has no *** accelerating. On the freeway, I have to downshift to get power to pass.
Here's the weird part - even when warm - it feels like if I don't MASH the accelerator or use part throttle, the car performs better. Also it seems that if I just wait, eventually I find more power while accelerating. Like a really long turbo lag (The car is na)....
I am replacing a DME temp sensor that tested bad. Also, just for kicks, I am going to replace vac lines and check the grounds around the engine bay.
I am still on the fence about the DME. It could be bad mechanically or the temp sensor that measures air temp could be bad. It really feels like the car thinks it is starving for air.