Hi! I apologize in advance for my poor English, I use an online translator. Need help finding a problem on a Buick Regal Custom 1991 V6 3.8. The Engine starts and works well. But after some time there are interruptions in the operation of the engine until it stops. The problem does not always occur, sometimes I drive all the way without trouble. This manifests itself in the following: the engine misfires, the relay clicks under the instrument panel, the check engine lamp flashes, sometimes the engine stalls and sometimes the cluster panel frozen. If maintain revs with the gas pedal, then after a while everything passes and the engine works well. There is speculation that the problem is the underhood wiring. I need a wiring diagram for trouble shooting. Can anyone share? And if there is a repair manual, then just great. Can be there is assumptions in than the problem?
A thousand thanks in advance!

I would scan it for codes.
Here'* the wiring diagrams for the engine management.

Thanks so much.
I'll check the codes and write them

Shows errors across all systems. It looks like a short-term loss of communications with the ECM.

OK......

But what were the codes?

Here is a list of codes:
21 TPS voltage was above 0.8 volts for 5 seconds when engine was running and air flow was less than 15 gm/sec, or the TPS voltage was over 4.8 volts at any time.
23 Inlet air temperature sensor signal showed an air temperature of -40° F for 0.4 seconds (On Regal the temperature was -31° F).
24 Vehicle speed sensor signal showed less than 3 MPH for 2 seconds when engine speed was greater than 3000 RPM and transmission has not been in park or neutral for more than 4 seconds. Or vehicle speed goes from above 18 MPH to 0 in less than 2 seconds without applying brake.
26 Quad-Driver sense voltage shows a low voltage when battery voltage should be present, or if the sense voltage shows battery voltage when a low voltage should be present for at least 5 seconds when the engine was running.
27 2nd gear switch was closed or grounded for 10 seconds when vehicle was in 4th gear, or 2nd or 4th, gear switch was open when engine was first started.
28 3rd gear switch was closed or grounded for 10 seconds when vehicle was in 4th gear, or 3rd or 4th, gear switch was open when engine was first started.
29 4th gear switch was closed or grounded for 10 seconds when vehicle was in 4th gear, or 4th gear switch was open when engine was first started.
31 PRNDL indicates a gear other than park or neutral for 13 seconds for 3 consecutive startups when ignition was on, engine was off and vehicle speed was 0. Or the PRNDL status indicators (A, B, C, P) showed an incorrect combination of Lo and Hi for more than 10 seconds.
41 Cam sensor signal was not received by PCM for the last 2 seconds while engine was running.

I would get a full charging system test done. A bad battery/alternator can wreak havoc on things, and not be immediately apparent. I have had 3 batteries die like that, and while they still started the car just fine, I noticed a lot of gremlins starting to crop up.

Also check/clean all cables/grounds as well, as well as the connections going to the power distribution blocks in front of the strut towers. A loose cable on one of those will annoy you like no tomorrow, one of which I routinely have issues with on mine.

Start from the basics and work your way up.

I second getting the battery/charging system tested. Those codes all can be set by a voltage (battery) problem.

Thanks, I'll check it out