cutting out in boost why?

[shackwrrr]

I just replaced the head on my shadow and Ive been driving it around. Ive run into a problem, if I get into boost it starts cutting out and then get to a point where it just plain shuts off if I stay into it. I pulled my plugs and checked them out and they are almost white except for one little section on each porcelan but they are also brand new and have about 15 miles on them. I then checked my fuel pressure and I have it at 60psi (crushed regulator) it holds perfectly steady at 60psi at 20 in of vac and goes up 1 psi for every lb of boost like it should. I took all the injectors out and ran them in a ultrasonic cleaner for 1 hour and put them back in. Still does it. I made sure the ground strap was there(actually replaced it). I lowered the gap on the plugs to .028 (br8es ngk). I did fine at 14 psi before I replaced the head and thats all I did I cant figure it out

its a 2.5 with a half assed hybrid 50 trim .63 stg2, stock injectors and an intercooler.

[boost geek]

Map sensor hose came off?

[shackwrrr]

thats all fine, no vac leaks and ive driven it around and I can build boost all the way to 14 as long as its before 4500 rpm. above 4500 any amount of boost it will break up.

[bakes]

What is your AFR?? if you get it to rich it will put the flame out!!!!

[shackwrrr]

well my Wb is showing around 11:1 under boost but I dont know because it drops to way over 18:1 at idle even though if I am around it at idle it makes my eyes burn. But if its so rich why would my plugs not be black??

[turbovanman²]

Check your coil, could be breaking down at higher rpm. Did you check the fuel pump for volume?

[Juggy]

thats all fine, no vac leaks and ive driven it around and I can build boost all the way to 14 as long as its before 4500 rpm. above 4500 any amount of boost it will break up.

find another HEP

[shackwrrr]

Check your coil, could be breaking down at higher rpm. Did you check the fuel pump for volume?


if there wasn't enough volume then the pressure would have dropped as it started to break up and it didnt. Coil may be fubar ill see if I can find something laying around v8 coil work?


hmm hep, I know they do weird things but its only sat a few weeks in a garage waiting on my head. On my way to park it with a nice trail of steam coming from the exhaust it could still break the tires loose in second at 14 psi but I guess anything could happen.

[kwiksilver]

I am chasing a similar problem on my near stock turbo I 2.5L Lebaron.

motor will rev to 4500 rpm, then surge like its hitting a rev limiter and finally bog and stop pulling completely. I replaced the HEP with a used one that came out of a running car, but I suppose thats suspect too. I gues a coil to be faulty. I have a new 190 LPH fuel pump coming from FWD performance.

[shackwrrr]

I am chasing a similar problem on my near stock turbo I 2.5L Lebaron.

motor will rev to 4500 rpm, then surge like its hitting a rev limiter and finally bog and stop pulling completely. I replaced the HEP with a used one that came out of a running car, but I suppose thats suspect too. I gues a coil to be faulty. I have a new 190 LPH fuel pump coming from FWD performance.

yea, Im pretty worried about it since there are so many people with the same problem that never really fixed it.

[bakes]

here is a very very rare thing to check as i have see it twice know move the speed and distance sensor wiring as far away from the starter wiring , as this will induce false voltage making the ecm think it's way above the speed limiter.

You realy need to get a scan tool that can data log and see what is dropping out.

[turbovanman²]

if there wasn't enough volume then the pressure would have dropped as it started to break up and it didnt. Coil may be fubar ill see if I can find something laying around v8 coil work?



You can still have pressure but no volume, :(

Bypass the baro solenoid, gave me fits last year, kept cutting out, found it by a fluke, :o

[shackwrrr]

You can still have pressure but no volume, :(

Bypass the baro solenoid, gave me fits last year, kept cutting out, found it by a fluke, :o

you have to have the volume there to have the pressure, you can have volume without pressure but you cant have pressure without volume. It confusing and hard to explain but I can wrap my mind around fluid dynamics pretty well.


think of it with voltage and resistance. If you have resistance(flow restriction) and turn on a load(injectors) the voltage goes down(fuel pressure)

[shackwrrr]

I put a new coil on it today and it smoothed out the idle a bit but it still breaks up. It just doesn't have the power it used to either and it has a bit more lag than before too but I just put the turbo cam that was in the head in because my 88tbi was bent.

[turbovanman²]

you have to have the volume there to have the pressure, you can have volume without pressure but you cant have pressure without volume. It confusing and hard to explain but I can wrap my mind around fluid dynamics pretty well.


think of it with voltage and resistance. If you have resistance(flow restriction) and turn on a load(injectors) the voltage goes down(fuel pressure)

Sorry, that is wrong. I do this for a living so take my advice as you like.

Thought of this earlier, so with what your trying to say, then a 255 fuel pump is worthless, as it doesn't put out any more volume at the same pressure as a stocker, right?

[shelbymonster]

do you use a splited vacuum line to map ? now i hookup the map sensor alone and run a lot better

[Shadow]

What type of vac line do you have running to the map sensor? The map sensor should have a dedicated line with the same ID as the OD of the nipple on the Baro that it hooks to.

I've seen ppl using the tiny plastic factory crap line to run to the map, or run a tree and have the map being the last sensor fed off the tree and the car will break up, up top under boost.

[Juggy]

can u rev the car past 4500 out of boost??

what happens if u were at 4700 and then tried to go over zero vac??? surges instantly?

i really think its HEP related

[Shadow]

Bypass the baro solenoid, gave me fits last year, kept cutting out, found it by a fluke, :o

Seen this many times as well.

[shackwrrr]

somewhat figured it out. I finally got off my butt and hooked up the scan tool and went for a spin. well with any amount of throttle it went strait into KR, huh so I retarded the timing and it made it better but still did it and I had it on the verge of building boost at idle it was so retarded. I went through the scan tool and saw that I full rich on the 02 and then I seen that my 02 volts were 4.98 volts wierd. I figured that my WB was giving my computer 5 volts and sending the computer full lean. well I just cut the wire for the 02 and reset the computer. Bam it works but I think my sbec is fubar because even with the 02 wire cut and isolated the 02 volts read .54 at some times then it will randomly go to 4.98 and stay there untill I reset again.

It still breaks up in first gear but all other gears it goes strait to 14 no problems with no KR.

[turbovanman²]

That sucks. Is it a stock computer or a chipped one?

[shackwrrr]

That sucks. Is it a stock computer or a chipped one?

stocker

[shackwrrr]

Sorry, that is wrong. I do this for a living so take my advice as you like.

Thought of this earlier, so with what your trying to say, then a 255 fuel pump is worthless, as it doesn't put out any more volume at the same pressure as a stocker, right?

A 255 has more potential volume, that way when you start to use more than the stock pump your pressure doesn't drop.



ok take a line and pressurize it and cap it off, zero flow right? now put an injector on one end and pulse it and the pressure drops a certain amount, right? Then take a pump and put it on the other end that flows x amount. If that injector was also x amount then the pressure would stay the same when the injector was open because for ever x amount of fluid in x amount out. Now take that injector and increase its size to z z>x and leave the pump at x flow. With the injector open since the pump only flows x amount of fluid only x amount of fluid will flow from the injector and since it is bigger than x then no pressure can build behind it.

Now I can see what you are saying if we are talking static pressure(engine off). Yes if the engine is off then a pump with less flow can pressurize a line to the same pressure as a high flow pump. Now with the engine running (dynamic pressure) you have the injectors constantly bleeding off the other end and report to above paragraph.


Yes you may do this for a living and have thousands of hours on your test light(headlight with wires watever) you have me beat there but its hard to beat a young open mind that has a gift for understanding complex theories and sciences. I also have a passion for understanding fluid dynamics. I have invested 40 grand into learning and I love to use it.

I do this for a living too.

[shackwrrr]

Figured it out, Slider cam with roller rockers. When I swapped out the old head my cam was junk and this cam came with the new head. Apparently the valves were floating because of the quick rate of the slider cam. I got a tbi cam from a friend and now it runs perfect and has more power than before my head swap (old head had about .030 guide wear).