Boosting without power and nasty lurching/bucking when off throttle.

[desertfox]

Sadly another post here.

As the title says. Yesterday as I went for a twisty drive through the mountains my car decided to just stop making power. Up till then my car had been running great.

I first noticed that when I would let off the throttle the car would lurch/buck pretty hard. Very shortly thereafter I found that preboost I had the usual (unimpressive) power but as I built boost I could hear it boosting like normal but it seemed like my power went down dramatically. I limped it out of the hills (nowhere to safely park and no cell service if it ceased running) and even downhill it would just brickwall around 3.5-4k. On a flat section it basically felt like it was a 50hp car. It also seems like my car used an excessive amount of fuel for the miles it went (I track my mpg) normally full to low fuel light is about 310 miles and at 190 miles it was already just under a quarter tank.

At idle the engine sounds fine, nothing particular in sound or performance. Boost was going to 5psi (what my forge wga came as...stock the site said) and vacuum was 18 idling and 20 while driving w/o throttle. I have the Joembc fpr (and this is far to dramatic to be the usual hesitation etc).

Of course, it has not thrown a single CEL to help my track the problem.

I checked vac lines and for everything obvious, such as loose spark wires or obvious holes in my boost pipes. With it idling so well I am not sure if a coil could be bad. I have not had time to tear into anymore but would love ideas anyone has for when I get home in a couple hours so I can hopefully pinpoint and fix this issue asap.

When I get home I will pull the plugs, check the coils and look around more carefully, but again nothing was really apparent yesterday.

 

[hornsfan10609]

It can still idle fine and run like crap under boost if the coils are bad. It will typically throw a CEL though if the coils or wires go out. It's worth a shot to replace them.

 

[desertfox]

Seems to be working fine now. Replaced plugs, wires, coils.

 

[mazdaspeedp]

ya i would say coils or bad maf

 

[desertfox]

Never did anything with the MAF, does look like as the coils wear out they can start to have issues when they get hot which would make sense going through the mountains. The butt dyno says the car does have a bit more pep and throttle response though, which leads me to believe one of those were at the very least worn out.

 

[Spooler]

Is your MSP stock? Mine was, so here's what happened when I hit the brick wall (even if my vaccum and my boost seem to be solid...):

1) WG actuator broke - blow in the vaccum line going to the WG actuator. If you feel no resistance, WG needs to be replaced
2) The plastic nipple connecting the cold pipe (from air filter to turbo) to the BPV cracked (it's frigging glued on....the guy who designed that piece is an idiot....). It's tought to see, took me a while to figure it out. Remove the rubber hose going to the BPV and only then you'd be able to see it. I took the cold pipe, removed the nipple, cleaned the section and glued it back in position with epoxy glue. I put several layers of glue to make sure it was secured in place.

Good luck!

 

[Spooler]

My bad, I see you seem to have fixed the problem. Driving through the mountains would have an effect on your power, density drops, so you are pumping less air into your engine. Any small leak would "feel" amplified under those conditions. Same for electrical stuff, dielectric insulation capability of air drops with altitude, so someting that wasn't arc flashing at S.L. could at high altitudes. Glad to hear the MSP is back on the road.

 

[desertfox]

This morning had random power cuts (spark or fuel it seemed like) while driving normally on the flat road. Threw a CEL have to pull that when I get home.

 

[desertfox]

Update: pulled the code and it is giving be bank 1 too rich... cannot say I am sure how to go about this one, especially as I already have the joe mbc fpr. WGA is a forge one replaced a couple years ago. Easy to check but I do doubt it would be that so soon. Will check the bpv nipples but I do not see how I could be running to rich from it.

Any tips ideas would be awesome.

 

[bwalt]

Sounds like you might have a leak in the intake system somewhere between your maf and tb. This will cause a rich condition due to metered air escaping, causing the engine to fall on its face when you hit boost.

Boost leak testers are quite handy:

 

[desertfox]

Ah I get it. Google is my friend. I have an ebay FMIC kit en route and I plan to relocate the MAF. Problem is surviving until I can get that installed.

 

[bwalt]

You'd be amazed how easily intake couplers open up and leak under 7 psi of boost. When the system is sealed, re-located maf or not, it works quite well.

 

[desertfox]

Well yes, but relocating the maf at least logically to me means a lower chance of issues, as there is far few places for it to lose air and matter between the maf and engine. Going to go over things this weekend to see if i can find any leaks. And at 7psi it is actually a dramatic amount of pressure since its actually 7lbs of pressure per inch so I very much understand how it can leak under pressure. Evil plastic pipes just make it hard to find out where.
Have some quality ebay fmic stuff on the way so hopefully as soon as that gets here I can install that and not deal with crappy plastic pipes anymore.

 

[bwalt]

Well yes, but relocating the maf at least logically to me means a lower chance of issues, as there is far few places for it to lose air and matter between the maf and engine.

True, there are benefits too. Keep in mind if there is a small leak(s) opening up under boost, even with the re-located maf, your turbo will take longer to build boost and have to work harder to hold boost.

 

[Valk]

this might contribute to some of the issues im having. once you hit boost the car just starts to slow down. its like slamming on the brakes at speed almost. maybe ill replace the coils/wires/plugs too. though i know i have clogged cats by how the car smells. so exhaust too.

not thread jacking, but most specifying that this information is useful to my condition too.

 

[SCMP3]

A friend of mines wwas doing the hitting boost an failing. Try just your plugs Valk as that's what his was. Unless you feel it's time to go aheadand replace it all

 

[Valk]

im not really a car guy like that so cant really feel what needs doing. ill probably go back to the stock heat range though. since i tried the colder ones the car seems to run lke s***. only had those plugs for around 10000km too.
i read somewhere though that the coils are supposed to have a particular resistance? i could check that ect.

 

[desertfox]

My issues seem to have been two fold. I replaced plugs,wires(one fell apart) and coils which seemed to resolve the more serious issue. Now I do not have any dramatic issue, just the rich CEL and some odd cut once in a rare while primarily at low rpm and full boost. Today I will be doing some more substantial poking to see what i can uncover.
I would stick with stock heat range and the copper plugs. I tried 1 step colder and iridium and neither really impressed me. Good ol copper stock heat range seems great for near stock boost.

 

[desertfox]

Edit: coils,wires, plugs did NOT fix it. Same crap happening today. It also idles like trash when it is having issues (stalling sometimes). Out of gear as it revs it goes up to 2800ish then sputters and fights and then climbs poorly after that. While driving it seems like it is ok, i shift then it brickwalls and fights then feels like it has 50 hp. I am ready to burn this car to the ground.

It also screws up while i keep it out of boost, so I suspect leaky boost pipe is not the issue. Still only has thrown a bank 1 too rich code. No sensor out of spec or anything remotely useful.

 

[bwalt]

Throwing parts at it wont help... you need to test things and understand how the system works to find the culprit and then solution.