You do have a head-scratcher, and there is something definitely amiss, but what? After you have pulled the trouble codes, try performing some 'old fashioned' diagnostics. Measure the intake manifold vaccuum and at the same time look at the output of the manifold pressure sensor. Do you have agreement? Low vaccuum?

I'm sure that John_G can supply a shopping list of tests to make.

Low vaccuum, or a sensor reporting a low vaccuum can mess up the system and make it misbehave.

In addition to bad valves, leaks, and late timing, a plugged catalytic converter will cause low and variable vaccuum.

Now, about that lock-up clutch. The car is old; its a 1994. Does it have a lot of miles? The lockup clutch could be worn out; The sensor that controls it could be bad. Do you have a detail drawing of it. If so, does it have brushes on a slip ring for activating the electrical part. If it has brushes, these may be worn out or hanging up in the brush holder. Those might work when cold and fail when hot. However, if the engine controller is seeing a low vaccuum reading, it may not lock the clutch.

Excessive slippage between a 3 to 4 shift may indicate that the transmission is on its last legs. That could be expected at 100,000 miles.

A bad problem to identify and locate is poor or intermittent circuitry in the wiring and connectors. For a car of that age, corrosion can do bad things to the wiring and connectors. For that matter, the wire to connector interface can be destroyed by "wire pullers". (In this sense, a wire puller is someone who yanks on the wire instead of gently working connector to effect a disconnect.)

When that car comes in, let us know what you find. it sounds like an interesting case.

Hi Kal.

Your a GM tech right? Worse than that we now call this system "OBD1" but it would be more correctly referred to as EEC"V" (5, but possibly IV=4).

The information you provided so far is sufficient to allow a tech to pull codes, road test to confirm if any of the reported issues are current, and then start the diagnostics from there.

First test KOEO (Key On Engine Off) and allow the car to report any current failures. The second test is KOER (Key On Engine Running) and again record any problems the system detects that are current.

From there the routine would be something along this example. Imagine you get an EGR low flow code. Re-run the KOER test while using a lab scope on the EVRV (EGR Vacuum Regulator Valve) and "T" in a vacuum gage between the regulator and the EGR valve. The lab scope would show you the EVRV command from the PCM, and the vacuum gage would show you the result of the command on the vacuum side. Repeat testing as required as you confirm what works correctly, VS what is not working correctly.

You need to do this with EACH code. You can stop short if you choose to in the possibility that some issues may overlap, but that's where the critical thinking skills really come into play. You have to be positive and be able to explain why code XXX is related to code YYY. Otherwise your only cutting down some trees to get to see the forest.

Now the problem where we all fail with things like this. How do you charge for the time required to solve each issue and not get treated as if you are scamming the customer? Every other person they will ever talk to will gladly throw out their opinion about how easy this all is, and how you must have seen them coming. Oooops, sorry got off topic there for a second. VVBG.

Anyway, treat each reported issue as if it is occurring on a different car until proven otherwise. Sell a given amount of diagnostic time up front, and diagnose as much as you can in that time. Then report you findings for what you completed, advise on what has not been completed, and go on from there.

Once you have codes and at least some testing results, post as much information as you can and I can work the rest of the way through it with you.

Well the car is here. It's 40 F outside with 100 percent humidity and raining. NO engine light and NO codes. The transmission locks up. Transmission is 4 years old motor was rebuilt last year. 80 lbs oil pressure at highway speeds 30 lbs. hot idle in gear. It's an EEC 1V (4). Computer self test comes back OK but i wonder. I guess i'll have to wait till it warms up and dries up. The engine light used to go out on it's own after about 5-10
miles and never come back on. Yes John i worked for the
genaral for 11 years. Ford 7 and Chrysler 3. I'm retired.
TRYING to anyway but people keep dumping this stuff in my yard and answering the phone. Think i'll send out bills
for answering the phone. I usually get a few calls every couple of weeks wanting free advice.