Engine misfires?

1991 is not capable of running any scan tool I am told unless it throws a light which it never has. Even then tech says that older computer don’t give much specific data even when you get a code. But again does not trigger a light as evidently the computer is not sensitive enough to pick up a miss that that does not even effect the tachometer. All new plugs, wires, gas filter, distributor cap, rotor.A couple sensors replaced included the o2 in the last couple years.

New fuel filter was put on and guy checked the fuel pressure. He said the problem wasn’t there. Far as ignition I have put new plugs, wire, rotor, cap. Again it seems related to when it get warm at operating temp after about 2 miles depending on outside temperature in mornings. Don’t know what else to check ignition wise other then the coil? It has to be something that is being effected only when it gets to temp hand half way. Like clock you can watch the temp hand get to halfway on gauge and look for it to miss sporadically. It does not miss before then or at a idle or at full throttle or going up a mountain. What would change as the engine temperature reaching normal that would cause a miss? EGR valve? PVC valve? Some sensor?

Again this slight miss is only after warm and once you get to cruising speed in drive about 50-70 normal driving. Do not see the miss in the tachometer. Anyway a torque converter would be locking and unlocking at 50-70 in drive. Transmission shifts good. Again you can stomp it and tachometer it out between gears up to a 100 and feel no miss. You never feel it on a mountain pull. It is always when warm and driving about 50-65 at 2,000-3,000 rpm's.

Thanks for the help. How can I get a video of vacuum gauge when it only does it on the highway? Does not miss idling cold or hot? I may just replace the coil (inside the distributor on this) to rule it out but you would think it would not be linked to temp gauge? I can see the coil maybe breaking down as it heats up but not like clock work when the gauge hits 1/2 way? What igniter are you speaking of? I talked to one Honda “expert” and they do work on mostly Honda’s that he said might have to take off the whole “throttle body unit? And manifold which he said was a job to “drill out the ports” so they could clean it? I got confused on that one.

I have done everything but replace the coil and igniter. However have have replaced hundreds of dollars worth of parts and no change. Let me break down what is happening as plain as I can.
1. The car never misses when cranked until the temperature hand gets about half way where it stays. Run smooth 50-65 until then. When temperature hand hit there about 2 miles driving starts the little sporadic slight miss. Does not effect tachometer.
2. Floor it from 0-100 and feel nothing.
3. I can only feel it in drive after temperature rise to set mark at speed 45-70? Just driving speed.
4. It seemed connected to temp of radiator?
5. Don’t know if connected but will surge when idling when cranked or return home. Again sometimes it don’t. That is sporadic too. Don’t even know if it is connected because it don’t miss when idling even hot or surging 1500-2000 rpm's.
6. I haven’t checked but don’t seem to get the gas mileage it should. Running out of options other then taking it to a expert who will probably replace everything on it again one by one.
7. Is it still possible a coil, igniter, or sensor. If the miss is connected to the water temperature?

EGR valve is one thing I have not cleaned. When you say “Clean the valve and the ports“. What valve name you taking about? What ports?
Whatever it is the temp hand can predict it to the minute. You can make a mark on the temp hand of normal operating temp and watch it get there. Takes about 2 miles depending on outside temps. Soon as it gets to that mark of normal operating temp it will start missing slight and sporadic in seconds. Best guess. Which valve would do that. EGR or the other valve? Or ports not clear on exactly which valve you talking about EARC? Where are the ports?

Story EACV?

EGR valve symptoms. My car does none of these?
Engine Performance Issues

Another common sign of a bad EGR valve is engine performance issues. A clogged or malfunctioning EGR valve can disrupt the vehicle’s air-fuel ratio, which can cause engine performance issues such as a reduction in power and fuel efficiency. The vehicle may also stall or hesitate while accelerating.

2. Rough Idle

One of the most common symptoms of a problem with the vehicle’s EGR valve is a rough idle. It is not uncommon for EGR valves to malfunction and become stuck in the open position. This can lead to exhaust gas recirculation, which causes rough idling even when the conditions are not desirable. It may also contribute to a smell of fuel as well

2. Pinging or Knocking Soud During Acceleration

Commonly known as a spark knock, a pinging or knocking sound may occur when the car is accelerating. This means the fuel is detonating within the engine instead of burning steadily. A faulty EGR valve causing this issue doesn’t allow in the right amount of exhaust to dilute the air-fuel mixture and lower combustion chamber temperatures. If this continues to happen, it can lead to other engine component failures. The EGR valve will need to be replaced or cleaned of built-up carbon deposits.

4. Check Engine Light Comes On

An illuminated Check Engine Light is another symptom of bad or failing EGR valve. If the computer detects an issue with the vehicle’s EGR valve circuit or position, it will set off the Check Engine Light in order to notify the driver of the issue. The Check Engine Light can be activated by a wide variety of other issues, so having the computer scanned for trouble codes is highly recommended.

The EGR valve is an important emissions component, especially for vehicles in states with strict emissions regulations. You won’t be able to pass a smog test with a faulty EGR valve. If you suspect your vehicle’s EGR valve of having an issue, have the vehicle inspected by a professional technician to determine if the vehicle needs an EGR valve replacement.

I better understand that now. I will try that by weekend and see what happens. Thanks will let you know if that has been the problem all along. Hopefully so.

I started the engine, but number 3 and 4 cylinders not firing.

Thanks a lot, I replaced the distributor with a second hand one, swapped the fuel injectors, but still the same with the engine check light still on. Do you think the fuel should continuously flow out from the pressure regulator with the ignition switch on?