caughing out under hard acceleration

[MOpowa]

i have a 1990 turbo shadow and from time to time under heavy acceleration the car will caugh out, it feels like it isnt getting any fuel when this occurs. The AFM gauge is constantly fluctuating but when it caughs out it reads very lean. I havnt had a chance to look at anything under the hood but was going to start with vacuum lines but if anyone has any suggestions of were to start it would be much appreciated. By the way this is my first post and i must say that i come from a world of 5.0 mustangs and im very pleased with the way this car performs.

[trannybuster]

Sounds like overboost, need to check all vacuum lines. When this happens does the car shut done for a sec or two, very quickly usually?

[ol"blue]

Need more info motor any mods but sounds like your hitting fuel cut,what boost does this happen

[MOpowa]

Ya it feels like it shuts down for a sec, im not sure on the mods as ive only owned the car for a week but it does have a aftermarket intercooler and 3" exhaust, The boost is usually around 10 psi wen this happens.

---------- Post added at 02:03 AM ---------- Previous post was at 02:01 AM ----------

What psi does the fuel cut off happen at?

[Khajjathefang]

Could be an old map sensor not reading boost correctly and engaging cutout early.

Welcome to TM!

Should be around 14 before it shuts down. This is a violent shut down right?

[shadow88]

You should be able to retrieve codes from your computer with your key. Follow the directions here on how to get them and what to do about them.http://minimopar.knizefamily.net/fault/index.html

If you find you have code 45 that's the clear indication you have reached overboost protection.

If you have zero relavent codes. 12 and 55 are considered normal around here. I would suggest you lower the gap on your spark plugs by 5 thou to about 30 thou and see if that makes a difference.

[MOpowa]

Yes its a pretty violent shut down. As for the codes i will check them in a bit. Is it normal for the air/fuel gauge to fluctuate or shoud it be steady? Thanks

[RoadWarrior222]

What are we talking on the fluctuation? It kinda "seeks" normally around the set AFR, by a little either side, but wide swings are not good.

There's a bunch of stuff related to fuel starvation that could be wrong, wrong pump, wrong tank, weak pump, clogged filter, and one guy even had a clogged fuel rail after we'd been through just about everything... There's probably 20 other weird things as well, so a lot to rule out, so try to be as specific as possible. And having just got the car, you can have some "previous owner" weirdness to contend with, like they stuck a small pulley on the alt to have current for a big audio system at idle and it friztes stuff out at high rpm etc. .. or the converse, alt is crapping out at high rpm due to bearing stall, and slipping on the belt. (Examine belt for chafing marks, sometimes idlers will do this to you too)

[MOpowa]

The gauge doesnt fluctuate bad i just didnt know if it was supose to be steady or if it was normal for it to be moving around, tomorow i will throw a fuel filter in it and check all my vaccum lines. I did notice that on the passenger side inner fender there are to black things that look some kinda solenoid have the vaccum lines disconected and there some kinda canister right under the pass headlight that has the vaccum lines disconected aswell. Does anyone have any input on what these are? Thanks again.

[RoadWarrior222]

Yeah the ECU keeps it set by waiting it for it to go one side of the AFR, then giving it enough to take it to the other side, and then when it goes that side tweaking it back again. ... and that's how it keeps track of whether the O2 sensor is working right... but it can also depend on how the gauge or display is "damped", some might seem steady, some might seem really twitchy.

[trannybuster]

^^Too add, make sure your guage is grounded well, better if it goes to the battery ground. Also would probably be good to add a boost guage, cant remeber if that car came with factory one or not, even if itstemporary. To reiterate what Roadwarrior said, who knows what the previous owner did but you def. found the best place for TD help. Also nose around in here as well as this site, tons of good reading http://www.thedodgegarage.com/

[RoadWarrior222]

Technical info on what the SMEC/SBEC does with the AFR ...
http://www.turbo-mopar.com/forums/showthread.php?63995-O2-kicks-lean-cruise

[MOpowa]

so i didnt find any vaccum leaks but the car has some kinda plastic waste gate or blow off valve thing on one of the charge tubes that i removed and the car hasnt cut out yet. All it seemed to do was make alot of noise (not my style) still only builds around 14 pounds of boost so ill probly leave it off.

[trannybuster]

Careful with that boost, 14psi on stock setup is pushing it to limit without adding more fuel, they run like scalded dogs when lean...if you get spark knock it will crack a piston. Id at least drop timing back 2*..snds like you unhooked the stock bov, these help the turbo last longer so boost doesnt stackup on the turbo. Need to make sure everything is hooked up factory style or this wont be your favorite car.

[MOpowa]

The BOV deffenatly isnt stock its not secured in anyway other than the hose going to it and looks like it was cut off the old car, but now the car is kinda spudering from time to time wen under high boost. Feels completly diff from before but still feel like a fuel issue. Ill throw a fuel filter in and see if that helps. But if it need a new fuel pump should i just go with a stock replacement or what? Thanks again

[Khajjathefang]

most folks opt for a walbro 255 unit

[turbovanman²]

Did you get any codes?

As for the narrow band AF gauge, most are hard to read as they bounce around, that is the computer doing its thing to achieve 14.7:1, under boost, the gauge should read solid, I like the Dawes AF gauge as it has 4 foolproof LED's but anyhow, a wideband is also a good idea.

Violent shut off is most likely overboost shutdown, it could be your boost gauge is wrong.

To check out your fuel system do this, and most of us prefer the drop in 255 Walbro from our vendors.



First off, hook up a pressure guage to the shrader valve or tee in at the rubber line-engine cool and engine off.

Start the car and note fuel pressure, it should be around 50 or a bit less, unhook the vacuum line to the reg and it should go up to 55 psi. Now shut the car off and watch the fuel gauge, the pressure should stay. If not, pinch the pressure line-if it drops, you have a bad FPR or leaking injectors, if it holds, the check valve the in fuel pump is bad and the pump should be replaced.

Make sure the key is off, jump 12 volts to the coil + terminal, a fused jumper wire is best but a piece of wire will work just fine.

Now, you should be reading around 55 psi, now squeeze the return line, the pressure should jump to around 90-100 psi. If not, the pump is no good. You can check the FPR if you have a vacuum pump if not, the above test works.

These tests assume you have no leaks and a clean/newish fuel filter thats not plugged up.

If you have an amp clamp and a lab scope, you can check the brushes by looking at the waveform pattern, it should look like a nice sine wave.

[MOpowa]

im not sure if its an overboost problem cause it will usually happen when i just hit the gas only building around 5psi. Ive had the boost gauge pinned @ 14psi and it doesnt cut out. But then again some times it does it some times it doesnt. If it was an overboost problem wouldnt it do it every time? The fuel pump is pretty noisy so maybe ill test it and and see what kinda pressure its building.

[shadow88]

If you check the codes, you'll know if it's an overboost issue.

[MOpowa]

so the car still has the same issue all the vacuum lines look good but the baro solenoid isnt hooked up i dont know if this would cause a problem? the car seem to do it more when the engine is cold and im having a hell of a time getting codes. so far ive gotten 34 then 49 then 49 again followed by 555 i know these arent right but ive tried reading the codes 100 times now and keep getting this im ready to drive the car off a cliff so if anyone can help or offer anymore advice it would be greatly appreciated

[turbovanman²]

Come out to my shop and I"ll do what I can.