lent my car to my parents
car was driving fine
then all of a sudden when going up a hill the car started to buck and lurch

got it back home
in neutral, it revs fine, sounds fine
put it in gear and start to drive, fine till about 1000rpm
then bogs down to 1500rpm
then smooths out to 2000rpm
then starts to buck and lurch

done some research and everything pointed to plugs
replaced with new nkg iridiums
didn't help
the plugs i pulled had a decent amount of carbon deposits on them, i think they are about 15k miles old
gaps looked good

evo 8 ssl
95k miles
all stock
only known issue is low compression in one cylinder

should i be looking for a coils/wires problem?
fueling problem?
boost problem? (note, I just recently had my car in the shop where they tightened everything for me)
some other electrical/computer problem?
MAF needs to be cleaned?

thanks in advance

 

hi, on vacation right now but hoping to get back to figuring out what's up with my evo when i get back. any help/suggestions?

 

maf sensor, map sensor, cps, fuel pump? have a shop put a scan tool on it to see what its doing.

 

any guides for checking maf, map, cps or fuel pump/filter?

either test or scan tool (willing to invest in one).

 

During a tuning session my car exhibited similar symptoms. Tuner explained the fuel injectors were momentarily stopping the flow of fuel. Why we have no idea but my theory leads me to believe a boost leak at the pcv valve may have been the culprit. Throwing out ideas. On the stock coil pack? Switching to a coil on plug setup brought my car to life but that's a different story.

 

yes, still on stock.

pcv would allow car to rev in neutral fine but then buck/bog in gear on throttle/load?

 

If you gapped your new plugs to .020 then I'd change ignition coils and wires . Wires go bad faster then coils.

 

If spark is the problem, the more load on the engine, the more likely to short.

 

This happened to me, I had a combo of a bad fuel pump and bad coil packs. I ended up breaking 2 spark plugs before I finally figured it out.

 

TLDR, turned out to be that the plastic BOV was broken in half. replaced with aftermarket and problem went away.

after a lot of reading about evos and non-evos having this type of problem, it seemed to come down to:
1. air leak of some sort
2. MAF not being clean
3. coils or wires
4. fuel filter or other fueling problem
5. plugs

I changed plugs because I had previously had a problem similar to this when accelerating at speed. (bucking and felt like I was hitting a speed limited) I had replaced the plugs about 10/15k miles ago but that is also how long the previous ones seemed to last. (stock ones lasted forever) Pulled the plugs, gaps were good, they were carbon deposited (but somewhat standard for evos from what I could find) and this didn't help.

Fuel filter, everything I read says that they are essentially "life time" filters and unlikely to be the cause. There is only one in the evo 8 and it is part of the in-tank fuel pump. Also from what I read, if fuel filter was the problem, even rev'ing in neutral should show some issue.

Coils and wires, this morning I was convinced this was the problem. But then read something where someone said they knew it was coils and wires because only 2 cylinders were showing different plug wear patterns. My plugs showed the same pattern and it was unlikely that all of them had gone bad.

Air leak, I pretty much skipped over because I had just recently had this done during a service. Like within 2k miles.

Lots of posts I found were about cleaning the MAF. Sounds like a good electrical cleaner (even if it says not good for turbo cars or Mitsubishis) would be fine as long as you didn't use the nozzle directly.

I started pulling things apart and noticed the airfilter looked a bit dirty but not that bad but looking down at the BOV it was cracked in half. I replaced with an aftermarket one and the problem went away. Reading some other articles, sounds like this makes sense because boost wouldn't come on till like 2000-2500 RPM which is when the problem would appear.

one of the best resources I found were the evo manuals here: http://www.evoscan.com/vehicle-manuals

Download the PDF and the manual and cross-reference them. I found that the PDF would have good workflows for troubleshooting with a scan tool but then the manual would have in-car tests that you could do without a scan tool like checking resistance of wires or testing the intake air temp sensor.

I'll probably also pickup an evo scan so that I can check codes and check some parameters myself.

Case closed, thanks for the help!