2002 MR2 Roadster. 1ZZ-FE, misfire and low idle when hot.

Hi guys, I thought I would post here for some input off those more qualified than me. I've been trying to solve this issue for months now and absolutely nothing I've done has fixed it. New parts include, MAF sensor, 3 new o2 sensors, new PCV breather hose, new spark plugs (gapped to correct spec 1.1mm), new fuel filter and fuel pump strainer, original fuel pump, original in tank pressure regulator. New air filter, new oil and filter, all vacuum hoses replaced and tested by spraying water on them. Have checked mechanical engine timing and it's spot on, new Denso fuel injector and seals, new EVAP solenoid. Now have a rich condition according to the computer, both at cold start and warm. The trims get increasingly negative as the engine gets hotter, I noticed that pinching the PCV hose shut actually made my trims go slightly positive. Tried some ice on the ignition coils whilst the engine was hot. This seemed to have helped a little bit but couldn't be entirely sure if I was imagining it or not. The idle speed occasionally bogs to 500rpm, engine doesn't appear to be overheating, I've never heard the radiator fans switch on so far (perhaps they're just quiet). The car is particularly sluggish when hot and misfires quite bad. It seems to run better on a cold night also. Scratching my head here as to what could be going on with this engine? Anyone able to give me a pointer here? Adam

Anyone? Runs perfect when it's cold. Misfire from idle to about 2500rpm, runs okay above that. Just down on power

What are your live data values?
Is it cylinder specific? Is it random? Any codes?

First thought is exhaust restriction.

Negative trims indicate you’re running rich. Is it actually rich? Verify 02 functionality.
I believe Toyota’s use downstream 02s as a part of fueling strategy as well. I could be wrong.


I would like to see MAF, MAP, Baro, ECT, IAT.

Hi, thanks for the reply. Unfortunately it's not thrown a single code at me, will try simulating rich and lean conditions. The car also runs rough on a hot restart (not sure if that's a pointer), I'll need to order a tool for the exhaust back pressure test but it's worth a shot. Tomorrow I'll gather diagnostic information to post here, I did notice my after-cat o2 sensor fluctuating a little like the upstream ones. Perhaps it would be worth using the endoscope camera to check the condition of the catalysts. As far as richness goes, the car smells like raw fuel when it starts up, although I put this down to cold o2 sensors. It doesn't smell like fuel once it's warmed up however. Interestingly one side of the exhaust manifold is showing richer than the other (2 precats, 1 sensor each). After holding the engine at a higher RPM the car stumbles and nearly stalls. Have lifted each ignition coil today to check for a dead or weak coil and they all seem to be sparking quite well, have got a proper tool to test them coming in the post. Also the misfire seems random, I've tried the mechanics stethoscope and all cylinders sounded about the same, the outer 2 perhaps a little more tinny.

One bank rich and one bank lean is also a sign of a plugged exhaust. However, there can be other causes. The hot soak running rough is definitely something to note.

I would use your rich bank and do a cylinder drop test. Maybe an injector problem which if dumping fuel could cause a plucked exhaust. I would suggest you OHM out the injectors when after a hot soak and see if anything jumps out.

I’m not sure what test equipment you have but DVOMs are fairly accessible if you don’t already have one.

Hi, I've uploaded some images of the scan data you asked for. I will be adding some more pictures soon of the o2 sensor in the manifold and the vacuum gauge reading. Also some black looking liquid appears to have come out the cat.

imgur.com/a/HWfr677

Adam

Hi, I've uploaded some images of the scan data you asked for. I will be adding some more pictures soon of the o2 sensor in the manifold and the vacuum gauge reading. Also some black looking liquid appears to have come out the cat.

imgur.com/a/HWfr677

Adam

You can try pulling the front o2s out of the exhaust when it is acting up to see if it runs better. that would indicate a plugged exhaust.

Nissan Technician

kamiwolf0893 wrote: Hi, I've uploaded some images of the scan data you asked for. I will be adding some more pictures soon of the o2 sensor in the manifold and the vacuum gauge reading. Also some black looking liquid appears to have come out the cat.

imgur.com/a/HWfr677

Adam

If the needle is steady then you’re in good shape. If you have the gauge hooked up and hold throttle steady to 2500 or 3000 rpms and see a slow decrease in vacuum over the course of 10 to 20 seconds you have a restriction. It should jump back really quick and hold steady if there is not a restriction.

Tutti’s suggestion is also a valid test and would be better than the vacuum gauge if you’re doing a test drive. Just something to think about.

Hi, thanks for the reply. Ive just tried it without the o2s and misfire had gone. Its come back now but given the o2s are unplugged thats probably due to a rich condition now?

The guage stays steady even holding at higher rpms. Will give it a test drive now without the o2s.

Have just reinstalled sensors and initially its idling smooth. Roughening up now

you have the o2 sensors actually unscrewed from the exhaust and not just unplugged, right?

Nissan Technician

Correct, I unplugged and removed them from the manifold and felt the car was running better initially, turned the engine off and plugged them back in, screwed them back into the manifold. The misfires disappeared for about 20 seconds. It seems like a restriction.

Ok. Paul also has a video somewhere on how he made a back pressure tester using an old o2 sensor for the threads and a vacuum gauge.

While the converter is the most common place for restriction, I saw a video where Eric o got burned because it was a muffler or resonator it something that was actually clogged.

Nissan Technician

This is an inline 4 cylinder engine. Bank 1 is cylinder 1&4 and bank 2 cylinder 2&3. Both going to the same converter. Since there's only 1.

The precats look like one main cat from a glance but with the heat shield removed, each bank has its own precat. There's a main catalyst further down, exhaust back pressure testing tool is coming in the post tomorrow so hopefully I'll be able to pinpoint where the restriction is, if there's a restriction. it'd definitely be nice to get down to the bottom of this issue, have been trying to nail it down for atleast 6 months. Also Tutti, thanks for the heads up dude, I did wonder if the silencer might have clogged up. Will put the camera up the exhaust pipe to have a look.

So i ran a backpressure test with the correct tool. 0 psi backpressure, all connections were tight and secure and the guage moves under snap throttle but not very high. I have however just pulled an ignition coil and plugged it into a spark tester (dont know the right name), the spark was wispy thin and mostly orange in colour. Could this be a weak spark?

Ok, no restriction then. Watch one of Paul's videos on spark testing with a test light.

Nissan Technician

kamiwolf0893 wrote: The precats look like one main cat from a glance but with the heat shield removed, each bank has its own precat. There's a main catalyst further down

Good to know! My mistake.