Flat Spot

gerzod · Post by **gerzod** » Sat Jul 10, 2010 12:40 am

Recently (in fact just after i got my car back from a service), i have noticed a pretty bad flat spot when accelarating hard that starts at around 2k revs and finishes at about 3-3.5k revs.
I have never really had this before, and I am not sure how to diagnose the problem.
I have:

-changed the spark plugs only 6 months ago
-service this week
-upper engine cleaner last service (6 months ago, although prior to now every service)
-full fuel system cleaner last service as well (nulon stuff, that works really well usually)

Does anyone have any idea what this could be? it seems to be most prominent in 2nd and 3rd gears.
I am hoping it is not the clutch slipping as i have heard replacing the clutch on these cars can be quite expensive.

My car is a manual 2ng gen gx awd ej22.

Thanks for your help.

sven '2' · Post by **sven '2'** » Sat Jul 10, 2010 6:43 am

Take it back and have the shop that 'serviced' your car deal with it?

Sven

last celtic warrior · Post by **last celtic warrior** » Sat Jul 10, 2010 11:15 am

Yeah, good point Sven...

I've remedied many a sickness in cars "serviced" by the mainstream shops. Don't let them try telling you it's a fault that's only shown up because they fixed other faults that were masking the newly found flat spot, and therefore it will cost you even more to have them "fix that too"...

It's most likely one of the work experience kids that they delegate "a simple service" to inadvertantly knocked a vacuum line off or something silly.

ScubyRoo · Post by **ScubyRoo** » Sat Jul 10, 2010 2:22 pm

maybe check clutch freeplay? Put a ruler perpendicular to the floor next to the pedal so you can see the markings and push down with your hand till you feel firm resistance. Should get around 15-20mm of play. It took me quite a while to get a 'feel' for correct adjustment and no longer need the ruler, but I found it helpful starting out...

Is the flat spot worse when accelerating up hill?

Battlewagon · Post by **Battlewagon** » Sat Jul 10, 2010 4:04 pm

I'd look at the timing.
Check the vacuum lines, like warrior said.

I nearly got ripped by a mainstream franchise mechanic who switched two vacuum lines "accidentally".
BIG flat spot, loss of power, drank fuel.
I noticed the problem, but left it and took the car back to see if I was being conned.

Yep.

Guy said I needed to replace the timing belts as they were stretched, as well as the tensioners because the "timing was fluctuating" and "messing up the injector timing".
Belts were new, and so were the tensioners, I'd just fitted them which is why I sent the car for a tuneup.......

gerzod · Post by **gerzod** » Sat Jul 10, 2010 5:50 pm

I took it back and he said he didnt touch any vacuum lines (which i am sure he didnt).
He is an honest mechanic, and was happy to give the throttle body a spray down today for free, and said to bring it back if that didnt fix it.
I am thinking of running some upper engine cleaner through it again just incase and maybe changing the fuel filter (they are $50 from supercheap though! not too cheap at all).

Can someone confirm that this is the procedure for changing the fuel filter as i have never done it before:
- pull fuze for fuel pump out, open fuel cap
- start engine and run until it conks out. try and crank it a couple more times
- undo hose clamps on filter
- remove filter and replace with new one
- tighten hose clamps
- replace fuze and fuel cap
- 1 more thing to cross off the list :S

also, what is the best way to dispose of the rags that get soaked in fuel and fuel filter? i take it they arent just safe to put in the bin given they will be giving off fuel vapors?

sven '2' · Post by **sven '2'** » Sat Jul 10, 2010 6:07 pm

Hang on...

You say he is honest, but your car is running worse than you took it in?

You seem to know little about cars (which is cool, not having a crack), but any mechanic worth his (or her) salt would be embarrassed that a customer is not satisfied - esp if the problem is as obvious as you report.

Did he experience it when he test drove it with on your return?

For you to go troubleshooting with little experience with what you are doing could be costly and end in tears.

If he is honest, and you faith in him (clogged fuel filter is engine tuning 101...), then follow his advice (which seems reasonable if not passive) and be politely persistent.

Sven

gerzod · Post by **gerzod** » Sat Jul 10, 2010 6:36 pm

sven,
I believe he is honest, and although this did start happening after he serviced it, i dont want to simply pin it down to being his fault. I will take it to him if the problem persists but i am also trying to become less reliant on mechanics by working on my own car.

Although i am not a mechanic, i would say i have a pretty good knowledge of cars. I am almost finished a double engineering degree, and have worked in the automotive engineering industry for 1 year. I do not have the hands on experience that a mechanic has, but i have a good working knowledge of the main systems and how they work. This is why i am trying to work on my car as much as possible (that, and to save money as i am a poor uni student haha).

My logic in replacing the fuel filter was that i was researching hesitation and read several sources that mentioned a clogged fuel filter is a likely cause. As i have no idea when it was last replaced i figure it is somewhat more likely than other causes, as i use the upper engine cleaner, have used fuel system cleaner, and have replaced the spark plugs, all of which are other common symptoms. If i can find someone with MAF cleaner spray i will give that a clean as well (I cant justify spending $25 on a can of the stuff, when i will use about 2% of its contents). I have checked the air filter and it is fine as well. I could not see any disconnected vacuum lines. I figure it might not be the clutch as i have tried flooring it in 4th and 5th gears and it doesnt seem to rev out, it just increases in revs really slowly. I also know the clutch was replaced 30,000km ago.

Sorry for the overload of information, just wanted to get rid of any uncertainties.

Suby Roo · Post by **Suby Roo** » Sat Jul 10, 2010 6:54 pm

Check the codes

my bet is knock sensor or afm

last celtic warrior · Post by **last celtic warrior** » Sat Jul 10, 2010 8:59 pm

Umm, greased your muffler bearings lately?

sven '2' · Post by **sven '2'** » Sat Jul 10, 2010 11:40 pm

gerzod wrote: Although i am not a mechanic, i would say i have a pretty good knowledge of cars. I am almost finished a double engineering degree, and have worked in the automotive engineering industry for 1 year.

Just trying help

A seven point dot point query on how to change a fuel filter led me to the conclusion that you may not posses a practical working knowledge. (which is 100% ok - at least you asked) This may lead you to, well, trying to install a filter in reverse, or trying to install a ill-fitting filter resulting in leaking fuel = engine fire.

I maintain clogged filter elimination is 101 stuff - he (she) should have covered this off.

Goodluck to you - hope you can pin it down

Sven

someguy · Post by **someguy** » Sun Jul 11, 2010 5:54 pm

gerzod wrote:Recently (in fact just after i got my car back from a service), i have noticed a pretty bad flat spot when accelarating hard that starts at around 2k revs and finishes at about 3-3.5k revs.
I have never really had this before, and I am not sure how to diagnose the problem.
I have:

-changed the spark plugs only 6 months ago
-service this week
-upper engine cleaner last service (6 months ago, although prior to now every service)
-full fuel system cleaner last service as well (nulon stuff, that works really well usually)

Does anyone have any idea what this could be? it seems to be most prominent in 2nd and 3rd gears.
I am hoping it is not the clutch slipping as i have heard replacing the clutch on these cars can be quite expensive.

My car is a manual 2ng gen gx awd ej22.

Thanks for your help.

I had a similar issue on the L Series, Ran fine around town but wouldn't get over 80km/h or 3000RPM no matter how hard i pushed it on the freeway, turned out to be a vacuum leak. Replaced the split hose and its now fine.

Probably less likely on a fuel injected engine like yours though.

gerzod · Post by **gerzod** » Mon Jul 12, 2010 9:42 am

thanks for the input guys. I will look into it. I will let you know what the problem was if i find out.
If anyone has any more suggestions im all ears

cheers

spike · Post by **spike** » Mon Jul 12, 2010 1:51 pm

yeah ive noticed the same thing on mine recently
will check all the vacum lines then.............

gerzod · Post by **gerzod** » Tue Jul 20, 2010 10:05 pm

Quick question on my investigation:
If it was a problem with either my AFM or knock sensor wouldnt there be a CEL coming up?

I have checked the vacuum lines and all seem to be in good condition and no loose connections.

I figure it probabl isnt a clogged filter or other "physical obstruction" (such as injector, air filter etc.) as it is a very on/off flat spot.
As in, it will literally spring in to life at about 3100 revs, and until then it will be really sluggish. Seem like it must be vacuum or electronic related (or part of some control system somewhere).

I have also tried resetting the ECU to no avail.

sven '2' · Post by **sven '2'** » Tue Jul 20, 2010 10:18 pm

gerzod wrote: I figure it probabl isnt a clogged filter or other "physical obstruction" (such as injector, air filter etc.) as it is a very on/off flat spot.

Filters Filters Filters!

See posts 23, 25 & 26

Sven

spike · Post by **spike** » Tue Jul 20, 2010 10:21 pm

agreed

some guy went to a lot of trouble with that, and we were all wrong..............

just on the fault thing, my aunties forester has check engine light on all the time, subaru told her to ignore it or put a sticker over it, not showing any fault

gerzod · Post by **gerzod** » Wed Jul 21, 2010 8:35 am

thanks guys, i just figured that if it was the filter then the car would feel sluggish throughout the entire rev range, or at the very least get worse as the revs invrease as the fuel flow would need to increase but an obstruction would cause problems.

I will probably have a crack at changing it myself (they are $50 though

, bad for us povo uni students). If i do decide to change it, how do you dispose of them? i would assume that they would be dangerous given they would still have fuel and fuel vapors in them.

Thanks for your input guys

spike · Post by **spike** » Wed Jul 21, 2010 9:20 am

actually it isnt that dangerous. enviromentaly its legal to put them in the bin, but id let it air a lot befor chuckign it or.............

same as when you do an oil change, just take your oil, filters and the like to the pertorl station adn leave them. legally they have to dispose of them however a lot of workers hate the idea of it.

steptoe · Post by **steptoe** » Wed Jul 21, 2010 9:30 am

So, would you please deatil this last 'service'. Given the previous 'service' record of system cleaners, and plugs fitted prior, did this service only consist of the bare necessity uni student service - oil and filter change . If so , little wonder you don't blame your mechanic, they must have only drained oil, replaced filter and refreshed oil, checked some or all fluid levels, squirt of window washer fluid and pumped tyres up, maybe made them shiny and given you a bill accordingly. Otherwise you'd be saying the fuel filter , plugs and air filter was done at the so flexible term 'service'

I'd say the technical detail you give in changing a fuel filter is correct, you understand the process involved and reasons why - just maybe exhange a few nights out with other uni students for a new filter - they will knowingly nod and understand why you must stay back and watch telly

It is possible that first stage blockage is only partial to allows fuel to flow for partial load, give it full load, full flow likely draws the blockage towards the outlet, still only giving so much fuel metering out, things may settle as load settles.

Before you discard it use a piec of white paper or cardboard (packaging from filter?) and drain it backflow on white paper to see what comes out fuel runs off down slight slope crud stays behind.