I have a 91 civic base with 1.5. Was driving and the engine started bogging down intermittently. I checked the plugs, wires, battery connection and sensor connections. I received no check engine light. I also replaced the fuel filter and alternator. When I start the vehicle, it cranks and runs just fine until the engine warms up and then it starts misfiring like a sumbitch and bogs down when I press the throttle. When I quickly turn the key back ACC then back to run, the engine comes back up to normal idle, and can accelerate rpms without issue, but only for a short period. When it's misfiring, if I disconnect the negative battery cable, the rpms come back up to normal idle, but bogs down if given gas. Also, if I turn the high beams on, the a/c fan and radio on, the engine runs perfectly. The more electronics running, the better it runs. I've exhausted my knowledge and look to you fine people fore help. Thank you for any advice you send my way.

 

Any coolant leaks? You have an IACV right? I’ve read that air in the coolant system can cause idle issues - but I’m not sure in this case because on throttle it bogs down.

Given that a greater electrical load allows the engine to run smoother, I’m wondering if there’s some sort of issue with the electrical load detector or voltage sense circuit for the ECU...? I’d probably give that a once over.

Maybe it has to do with the computer getting incorrect temperature information when warmed up and the ECU still thinks it’s cold? I’m assuming the coolant switch and coolant temp sensor are the sensor connections you checked? Your fans come on right?

When you checked the spark plugs - did you notice anything on them? Did you check to see if you were getting spark when engine is hot/misfiring? Perhaps it’s something in the distributor that’s not connecting properly when hot.

 

Thabk you for your response smackin. I didn't know there was an electrical load detector or voltage sense circuit. Do you have a recommended start point for those?

 

The ELD is integrated into the underhood fuse box. I believe it's replaceable in theory, but it's much easier to swap the entire box. I've read that CDM cars don't have it, so this may not be the issue if you're not in the USA. Voltage sense circuit is a new one to me though.

If you have not checked voltage under these various conditions, I would do so. That could help narrow the issue down.

Definitely check the distributor as Smackin suggested. I've had a loose rotor cause odd intermittent issues, though not as extreme as you've described. While the cap is off I would also ohm out the coil to verify that it's within tolerance.

 

Electrical load detector is in the fuse box inside the engine bay, I’m not exactly sure of what it comprises of however. It should have a 3 pin connector going to it.

Do you have a manual to refer to? Might have some wiring diagrams and diagnostic procedures in there for it specifically. It would also show you the voltage sense circuitry.

(“voltage sense” is the term we used in regards to FCA vehicles it’s prob called something else in the Honda universe. Basically it’s a circuit going from the alternator to the ECU, so the computer knows the output voltage)

 

So I tried bypassing the ELD with no joy. I've covered virtually everything including the ECM. I took It to a shop and the owner was kind enough to let me borrow an ECM. I swapped it last night with the same results. The shop owner, who specializes in early Hondas, gave me the same response everyone else has given. Man, that's really wierd. I'm going to drop it off with him today and will post the findings.

 

Set the timing to sit perfectly see if that helps

 

Take the distributor cap off and see if the rotor is on tight. They are notorious for getting loose.