quick dsm newb help... boost leak/fuel cut diagnosis

[foxfan88]

Finaly got my talon where i can drive it. The car is bone stock besides a set of plug wires, and a straight pipe for exhaust (sounds crappy.)

Ive also replaced the plugs that are gapped around .032"

When i drive the car it seems to run really good, but when i got WOT, the stock turbo seems real laggy.

According to the stock boost gauge (need to get a real one), I'm not hitting full boost until 4500-5000 or so. I know the stock boost gauge isnt supposed to be accurate but i figured it would be a decent indicator of full boost or not.

In the midrange i will see around 6-7 psi on the stock guage and then it will raise to 12-13 ish around 4500-5000.


And the last few times i have been driving it, the car at higher rpms will start jerking as the engine missfires, it feels like its not getting fuel. It will pull smooth, then get a random missfire, keep pulling a bit more and miss again. The higher RPM, the worse it gets, i kept in it the last time i drove it and it go so bad the car felt like it hit a wall, feels like the fuel was completely shut off.

I was thinking a boost leak, if the turbo is leaking boost bad enough, I could see the turbo lagging, and since its leaking out, the turbo would keep spinning faster and faster until the wastegate manages to open. pulling too much air through the maf causing the fuel cut.

At first i only noticed at like the top of 4th gear, now i am feeling it in all the gears. Thats strange, seems like if it was a boost leak it could have gotten worse.

Just seeing if this sounds like the problem or not. I am going to make a BLT and see what i can find. i did just have whole engine out of the car so theres a distinct possiblity something is leaking.

thanks.

 

[flying_eagle]

well you need a logger for one, they help alot in diagnosing whats going on and two once you get an aftermarket boost gauge you will realize just how off the stock on is. Also do you have a mbc

 

[foxfan88]

Nope, all stock, still using the BSC, the restrictor is even still in it.

 

[mikelv]

It's not going to be boost leak that would cause you to run out of fuel. When you have a boost leak the ECU will ADD fuel because the MAS is reading all jacked up. So think this: Boost leak would make my car run super-sluggish and rich (as what happens when you lose an intercooler pipe).

Fuel cutting is the ECU's last defense before destroying your engine, so if you manually changed the amount of boost a stock car will see, without any engine management you'll get this. Stock boost was the orginial design from the factory for the ECU to handle, so I doubt you have this.

Unhook your negative battery terminal for a few minutes to reset the ECU. If for some reason, you did hit fuel cut, (which I doubt because you said it was all stock) then it will be a set parameter in your ECU until you reset it.

Do you have any Check-Engine Lights? (CEL) If so, get those codes from a local shop, or a personal ODBII reader. (availiable at Auto Zone) Once you get the code look it up on the DSM VFAQ's or in a Chiltons shop manual.

VFAQ Site - Visual Frequently Answered Questions

Also, regap those plugs to .028. Sounds like you are misfiring at top end under boost. The boost is probably blowing your spark out causing misfire.

Don't worry about testing boost leak just yet unless you take a look and see something obvious.

 

[foxfan88]

I see. I was under the assumption if a leak was bad enough the turbo would have to work harder to satisfy the boost pressure to open the wastegate, may be say 10 psi in engine (or whatever WG is set for) but the turbo could be over spinning causing airflow readings to bee way too high causing the ECU to hit the fuel cut. It doesnt seem like the tame stock setup would be able to do that.

FWIW i got the parts to make a boost leak tester, need to finish that. Today i took the intercooler tubes off and the MAF etc etc, i found nothing wrong. I put it all back and made sure it was all tight, i doubt there was a leak ( at least nothing to cause any problem)
FWIW the engine pulls pretty decent vac at idle. Like i said i dont have a read boost gauge but i can pull the BOV vac line and it will suck on the tip of my finger pretty good, i would imagine though that a boost leak would really manifest itself under boost (unless it was some HUGE leak)

Anyways i messed around with the car some more, the top end miss is very upredictable and intermittent. Some times it does it really bad, and other times it wont do it at all. No rhyme or reason to it.

I forgot the mention, this talon has been sitting for 5-6 years perhaps longer.
For grins today i pulled the fuel filter off and some nasty cream colored liquid came out, didnt look right at all. The filter was fairly clogged (sort of harder to blow through.) this strange colored fuel would leave stains on whatever it fell on as soon as it evaporated

I went to the back and pulled the pump out and the gas in the tank is real cloudy and the fuel pump sock/screen is nasty orange colored and leaves a residue on your fingers.

Perhaps i am seeing the issues due to the trash in the tank, i have ran a little fuel through it, have gone about 80 miles since i have got the car going. I did put a bottle of fuel injector cleaner in the gas, as well as some seafoam through the engine.

I'll lower the gap on the plugs thats easy enough to do. while on that subject, i checked them earlier today and the insulators are really white, like a lean white, not a tan colored like a normal plug should be. This was checked after just normal driving and idling, so as for the what the plugs would look like after WOT, i dont know.

Perhaps there is something to the nasty gas tank issue. I am confident a sitting for 5-6 years cant be good for anything.

There are no CELs since i got the car running, i couldnt get a scanner with the correct plug for the 91 car. I got the codes according to the chilton book and probed the two pins on the diag plug with a voltmeter and watched the swings of the needle.

I think i got a code 31 which the book said knock sensor, and maybe a code 13 which was IAT sensor. I dont know for sure if i should be seeing a CEL for these or not. As a test i ran the engine with and without the knock sensor plugged in and notice no change in engine behavior, if that means anything, should that throw a CEL or something?? I could definatly see a honky knock sensor causing some lost power if the ECU is pulling alot of timing if the bad knock sensor is lying that there is knock, enough timing pulled would cause some missing i am pretty sure.

And i was sort of confused on reading the codes. If i read the codes and tried to read them again with another key on cycle, i couldnt get the code back, one time it even started the fast sweeping indicating a system pass. I dont know the method to this as to why the codes would clear.

Like i said before it makes it hard not knowing what a stock setup should run like, my buddies have some DSM, one has a NT car, another has a 2g car with all the bolt ons and a 50trim setup, its ALOT faster than this car obviously. Then again i am used to alot faster cars than a stock talon which should probably be in the 15s, my fox mustang at the moment runs high 12s-low 13s, and a few years ago had a vortech blower on it and was in the 11 sec zone. So maybe it is running correctly (aside from the missfiring) and i just expected too much.

 

[rEclipserGST]

If your car has been sitting for a long time... you should change and check a few things:

Compression Check
Boost Leak Test
Change wires, plugs, oil, fuel, filters, battery, and inflate tires
Check turbo for shaft play

Now your ready to beat on it again

 

[foxfan88]

I got the car as a complete car but the bottom end had a knock. After i got the car home i ripped engine out and tore it down, being a complete DSM noob it sort of helped that i was forced into doing this job, lets me get to the know the car a little better, after tearing it all out and putting it back in i sort of know where everything is at.

Anyways i know the PO of the car and he gaurenteed me a running car, the deal was he would give me a different shortblock to put into the car if i had to pull the motor from mine.

I changed the shortblock and and replaced the timing belt while i had it apart. I got the car running and also had the changed the ECU since the stock was wasnt working.

I changed all the fluids, oil, trans, tcase and rear diff fluid. Tires are air up , i bought a new set of plugs and the wires are a nice set of wires the PO had put on the car when he was trying to get it running.

I havent actually ran a compression test yet i will need to do that, but the motor seems to run well and i dont see a reason it would be low, as there is no smoking or anything like that. I'll also get my BLT done and try to do a BLT on the car. Get the new fuel filter on and run this tank out of gas and then add some more clean fuel and some more cleaner. I have a feeling it just needs to get the cobwebs out it.

I had the turbo off the car and I didnt feel and in-out play, though there is some small side to side play but every turbo i have felt has a little side to side.

I am also using the battery from my mustang when i tinker around with the DSM, its a new battery and works well.

The car runs well the only issues i seem to be having are the missfire at high rpm (intermittent) and also the car idles down really low when i turn the AC on, i messed with the BISS and set the timing correctly and the car seemed to idle and act correctly without the AC on, idles around 7-800ish, with the AC on it bogs down to around 600. When the AC clutch disengages it will idle up again.


sorry for these long posts haha but i appreciate all the help keep more ideas coming.

 

[rEclipserGST]

The idle will go down just because your putting load on it aka the a/c. These alternators are known to be weak. There was a thread recently referring to a saturn alternator swap.

But the Biss screw is only going to change so much. You want 750-900 rpm idle range.

 

[foxfan88]

I understand that, but it feels like an awful heavy load. the car feels like its pulling alot of weight behind it when the AC is running. I dont know if this is normal.

BTW i changed the fuel filter out and i seemed to notice the car ran a little better. The WOT power may have been better, nothing much if it was, seemed to run smoother overall. But after about 20 miles of driving, i went WOT again and the hesitation came back, nothing horrible. just a few random bucks when WOT.

I am wondering if the fuel pump is getting weak. The PO said the original was locked up with the car sitting, and found another pump laying around just to get the thin running, the age and condition is unknown.

Well i found the reason for the knock sensor code 31. I was messing around and was holding the knock sensor harness plug, and it appears someone may have redid the wiring for the sensor with a butt connector. anyways the connection came apart in my hand, with little force and i wasnt even trying to break it. I dont think the ECU was even getting a signal from the knock sensor.

What exactly would the ECU do if it wasnt getting feedback from the knock sensor???
Would it force some sort of limp mode or pull timing across the board or something. Regardless it cant be good. Perhaps this could be some of the sluggishness perhaps weak WOT. I will fix this problem asap.

Work on the car again today, pulled the knock sensor off and fixed the wiring problem with it, it wasnt oozing anything so i went ahead and kept using it after i fixed the wires.

Car runs ALOT better now. Alot smoother through the RPM range while driving and i noticed a good SOTP gain at WOT. Turns out the ECU was pulling alot of timing all the time causing the sluggishness.