khellapeter

i just bought this 97 Crv, automatic, pretend 4 wheel drive.

It has a misfire at cylinder 1 3 4. Random times.

I replaced fuel filter, distributor, plugs, and wires.

Checked fuel pressure
found fuel pressure ok

cleaned iac

did a compression test 175 on all cylinders
leakdown passed

done research and many people say it's the valves that get burnt.

The car is getting horrible gas mileage, less than 19miles per gallon.

can some one guide me in the right direction to diagnosing the issue? Your help will be greatly appreciated.

Note: I believe the misfire only occurs at idle. Slight hesitation/ vibration felt. Especially in neutral and park.

fcm

Check the ECT sensor and/or its wiring.

It sounds like you are running rich, [poor fuel mileage and misfire].

How is engine starting when cold and when warm?

The ECT sensor tells ECU engine temp. the ECU will change Air/fuel ratio depending on that info, rich to start a cold engine leaner to start and run a warm engine.

Signs of a problem with the ECT sensor are poor fuel mileage, crappy running engine, easy cold starting harder warm starting. 94

khellapeter

although if it was my ect sensor my coolant fans wouldn't turn on.... and they work perfectly fine.

Caoboy

Do a valve adjustment as preventative maintenance.
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JRCivic1

The fan switch is different from the ECT sensor. The ECT sensor tells the ECU what the water temperature is inside the engine, and if it is in fact bad/damaged, it can send incorrect values to the computer that affect fuel compensation. Low ECT values add fuel during engine operation, and this function does not affect the cooling fan operation. The chances of both the fan switch and the ECT sensor being bad is unlikely... don't confuse one for the other. Also remember that the temperature gauge on your instrument cluster works from a THIRD sensor... a single wire plug on the side of the cylinder head.

The proper test of the ECT sensor would be to crank the car when cold, and using the OBD scan tool you pictured above, monitor engine temperature from cold start to fully warmed up. The values should slowly increase from about the same as the current outside temperature up to between 180-200 degrees when fully warmed up. Your electric fans should come on at or just shy of that 200 degree mark. If your gauge appears to show a warm engine, and the scan tool shows an ECT value 40+ degrees LOWER than 180 degrees, I would consider that sensor suspect.

Also, an exhaust leak... such as a cracked exhaust manifold, will allow outside air into the exhaust stream and thus trick the O2 sensor into thinking the air/fuel mix is lean... and the computer will continue to add fuel with short and long term fuel trims to counter these readings. This false reading adds far more fuel than needed to the engine... reducing fuel economy and causing misfires. If you cannot detect or find an exhaust leak, consider the possibility that the O2 sensor itself is faulty... a condition some call a "lazy" sensor... relaying false values to the ECU and creating improper fuel enrichment correction. You can test this by monitoring the short term and long term fuel enrichment values while the vehicle is being driven at warm operating temperature. The short term values should be LESS than +/-10% and the long term values should be even smaller. Both should be the same direction... either positive or negative. Positive is ADDING fuel, negative values are cutting fuel.

DCFIVER

Sounds like the valves are too tight. Do you have a MAP volts reading on that little tool of yours.?
What is it at idle in D?




****Dont worry about the ECT. Its a non issue. OBD2 seems to have left may here way behind and in the dark.....

khellapeter

Idle was low in that picture. I adjusted to 820 rpm.

I will check ect and map voltage ASAP.

Thanks guys for for your input so far.
Dont worry when I get a solution I will definitely post it cause none of these threats have the answer.

khellapeter

Alright so when cold, ect is 30c
when warm ect is 80c+
Ect is working fine...

the o2 sensors reading properly too I believe... but there may be an exhaust leak that's not visible to me... how can I check?

MAP sensor reading 34 to 37 kPa...
not sure what specific value is

Cody Orr

I'm kind of Having the same problem, ok I own a 99 crv 2wd auto,about 9 months ago and yes time line is correct,I got a cel and took it to autozone,got codes for random and multiple misfires,I'll post codes when I find them,googled codes and all I saw was burnt valve info,took it to a shop had valves adjusted only a few were slightly tight,had compression and leak down done and both passed,over time crv got worse,replaced plugs,wires,cap and rotor also air filter,was ok for a little,I did some research and found out if your fuel filter is clogged it can cause all kinds of problems, I replaced fuel filter and got way better but still ran a little rough, looked at cap and the post had build up and were miscolored,replaced cap and rotor and it ran even better,so I know for a fact it's not valves cause it's been running good besides at idle,shakes just a little,has a lot of power,doesn't smoke or anything, so far I've replaced mid pipe(old one was bent to ****)new cat and o2 sensors,fuel filter,plugs two days ago,cap and rotor,battery,air filter, clean fast idle control valve and everything else lol besides injectors, inside of dizzy is clean and all parts are in good shape,my question is what else could cause idle problems, intake manifold gasket ?,any advice is appreciated