problem at around 20 psi

[butlar]

Here is the deal. Boost leak test checks out fine, timing is dead on. The car (1992 talon tsi) is perfect below 20 psi. Pulls strong and hard to redline. But if I turn the boost up to around 20 psi the car will buck a few times ( its like fuel cut but I have a burned eprom chip with fuel cut eliminate). Its really weird and hard to diagnose. And sometimes it will be fine. I have pressure tested my system to 30 psi and it holds fine.

I was wondering if it could be the tune but the car stops dead when it happens then starts to pull again. Its not the ecu or MPI relay because ecu is brand new from motoguys garage and relay checks out. but it seems way more violent of an abrupt stop in power to be tune, like I said it's just like fuel cut or like when the mpi relay clicks when ecu restarts ( withs bad caps ), but that isn't what is happening.

Also when in neutral ( car is standard) car will rev fine to 5000 then a weird miss comes into it but it still revs to 7000 just with a miss ( its hard to describe). Spark plugs are new ( gaped .028), wires are not new but not that old, power transistor and coil have been switched out. I was thinking mabey the studder box was fooled up in my chip but the clutch wire is not even hooked up.

Only things I have not checked yet are to pull the fuel pump (walbro 255) and see if maby the sock filter is clogged or hose has a pin hole in it, or it could be a FPR or injector issue but that appears to hold pressure fine.

Any input or ideas would be greatly appreciated.

 

[haswesley]

What are your Air-Fuel Ratio numbers at 20psi? I had the same problem a while back and discovered it was simply my plug wires. They looked good, but plug wires deteriorate quickly in our turboed cars. It seems its fuel cut, but really a loss of spark. I use Bosch wires from Autozone with lifetime warranty. Every year I return my wires for a new set at no cost!

 

[4gst]

I had the same problem in my 2g. It would happen around 19 psi, i did everything to try to fix it didn't pay attention to the wires because they had been changed not to long ago. As soon as I changed them the problem went away and hasn't came back. Now i'm on 22psi, new wires fixed the problem.

 

[butlar]

I will definitely try a new set of wires it has been on my mind since this started. Also I had a look at the FPR today. Took it apart, examined the diaphram, everything looked good, sealed it back up nice and tight. Put i back on the car and started car, hooked a air hose to regulator and supplied positive pressure and fuel pressure increased 1:1 as i added air(while car was idling). So it seems to check out. However I did notice that sometimes the car holds fuel pressure after you turn it off and sometimes it does not.

I have read this is a common thing but I wonder if it is related to my issue, sometimes it will hold 20 psi for a long time and others I cannot get out of car fast enough to check it when I shut the car off and it reads 0. Perhaps leaking back through pump? maby at 20psi something in pump starts leaking, hose is coming off or split, o-ring, but I really do not want to pull that pump out. The car starts fine so it builds pressure fast and good, never cranks more than 2 times and she is running.

Well hope to hear some more ideas, thanks for the help so far.

New magnecore wires on the way, hopefully they solve the problem. Ill keep you guys updated, thanks again for the help

 

[rza808]

check air temp if can if the air is to hot going in mani can cause knock at that level.

 

[butlar]

UPDATE: got new magnecore wires...problem no better, worse. Car is stumbling now even under little boost. I am wondering when checking voltage at battery with car running, should alternator be putting out more than 13.6V, also if I increase rev's voltage will not change, stays at 13.6

Also If i pull plug wires it seems that 2 and 4 have stronger spark than 1 and 3, which is weird because they are on different coil. I would expect maby 1 and 4 to be strong, or 2 and 3, but 2 and 4, weird to me. So I am guessing weak coil or power transistor or going bad alternator not puting out enough to power both cylinders well on each coil and only powering one.

Any help would be greatly apreciated

 

[JayRolla]

So if you install the old wires the issue is not as bad? What type of plugs are you using? I would lower gap to around .024 and see what happens. Thats what I run and I know others that run even lower gap. Also make sure you are running ngk 7es plugs. I have had issues with accell, magnacore and even MSD wires. Ive found NGK spark plug wires work the best.

 

[IgotBoost91]

this might sound crazy but check plug gap.

 

[butlar]

it definitely seems worse with the magnecore, but i cant see them making it worse, they are a tryed and tested wire. I am gonna test the alternator again tomorrow, proly try the old wires just to see. I have switched coil and power transistor a little while ago, and since problem remained the same I assumed it was not the coil or power transistor. and re-gap plugs BPR7ES. Also perhaps when i switched wires something screwed up in the coil.

Its a really annoying misfire. Car will idle good with slight miss every now and then, but when revved even in neutral to 4 or 5000 rpm a very noticeable misfire will develope. And when driving car will stumble horribly and struggle to build boost.

So car has gotten noticeably worse since beginning of thread, . I guess I could check resistance in wires on the posts of coil that I figured where stronger and then check on ones I though where weaker. But I have a feeling the alternator may be the route cause of the weak spark.

Any other suggestions would be greatly appreciated, thank you.

 

[IgotBoost91]

test the cas and coil?

 

[butlar]

would the CAS act up only at higher rpm? that could be the problem though, I have another one I could try putting that one on. I will definitely test coil tomorrow. How do I test CAS, I know of the remove it and spin it by hand test, but I know it is some-what working because car runs and starts fine.

Thanks for the help, keep the ideas coming.

Update.

Checked alternator today, checked out fine, as did battery. Tryed another coil pack and power transistor, still had the miss. regapped plugs to .024 and that seemed to make a difference. Car still will start to break up in neutral at around 5000 rpm but when driving it seems alot better.

I was wondering if maby i had some sort of leak inside my fuel tank on that hose that is on my walbro or the sock filter in clogged on the pump. When making a pull in 3rd gear now at 16 psi, car will stumble now and then, sometimes will be fine, stumble usually happens almost at full boost, once again no boost leaks present.

Also tryed another GM MAF i had laying around, seemed to be the same.

Changed out CAS and timed car 5 degrees BTDC, and did not seem to make much of a difference.

this problem is really weird any other suggestions would be welcome, let me know what you think, thank you.!!

 

[butlar]

UPDATE:

Decided to change valve cover gasket today. Pulled off valve cover, and low and behold, rocker arm from cylinder 3 intake had come off, it was just sitting there minding its own business. put back on and car now revs fine to 7000 in neutral, and pulls hard on the road

But, if I try to boost over say 15 or 16 psi, there is still a slight stumble sometimes, and sometimes it seems the car builds more boost and sometimes only like 13 psi. I am wondering now if my V-trim is leaking. I have not taken it apart and sprayed the surfaces with gasket maker and put them back together. I guess next on list is to pressure test turbo, but the gm maf hooked up to throttle body should compensate for that, even if it leaked then didnt then did. I dunno its really weird.

Also I am only running stock springs with 272 cams, but I do not rev the car high, could my misfire be from valve float?


keep the suggestions coming , thanks again.

 

[JayRolla]

Well when I burnt up a valve from running a little lean I had the same issues as you. I would do a leak down and compression check.

 

[butlar]

compression is fine 150 across the board. It was even fine when rocker arm was off I guess valve was stuck closed and not bent. But the miss is still there but it not near as bad, when in neutral there is still a slight miss. But car will rev nicely to redline.

Another thing I noticed was exhaust manifold is leaking a bit, noticed some black around gasket on cylinder 2 and 3. Could this pre-turbo leak be cause misfire in higher boost conditions. Because I am running a gm maf right before throtle body so I dont think it would effect that much, perhaps

Any other opinions would be great. Also my lifters are rather loud, I am running 272 cams, and lifters are not shimmed, could this be causing my miss?

Finally i noticed, if say I am in third gear and jump on it at around 3000 rpm, when boost builds and at around 4-5000 rpm that is when car will misfire/stutter, like a few quick bucks then it will continue to pull hard to red line. If I slowly rev past 4-5000 then jump on it , it wont miss at all. I was thinking mabey valve float and if i slowly rev it up then jump on it, it isn't so bad.

Any other opinions would be greatly appreciated, thank you.

 

[ramsack]

first off, an exhaust least can sound like lifter tap. if a rocker arm fell off, and you have a lot of lifter noise, i would look into cleaning out your lifters or getting new ones. they could be causing phantom knock or just not letting the valves open properly causing all sorts of weird problems.

here is a good writeup on cleaning out your lifters: http://www.dsmtuners.com/forums/articles-engine-fuel/365986-diy-lash-ajusters-lifters-cleaning.html

also you should check the oil pressure getting to the head before anything. something could be blocked up.

 

[1stGenTSi]

Have anything to log with?

 

[butlar]

I have my stock boost gauge set up for knock, and when this bucking occurs there is no knock, and i have tmo data logger, but do not have a log on this computer to bring up, ill get one soon and post it. Cleaning the lifters is a good idea, but if the problem comes and goes I dunno if I can see that being the problem, shouldn't it always be present?. Although it seems it almost always does it if i jump on her in 3rd gear.

I am starting a new job this week so I dunno how much time I will get to have at the car, and I know it is an exhaust leak because I checked the nuts on exhaust manifold to head and got a few turns on some of them, and one stud was stripped in head so I'll be drill and taping that sometime soon, but I still cant see that leak causing this miss.
Also as far as the logs I do have go, ill try and get one up as soon as possible.

Finally lifters are noisy but not bad enough to screw with my knock , I know this from watching when i do pulls, hardly any knock, sometimes some when she bucks but the car is missing so that would cause phantom knock.

Its really weird, no CEL's either. I'll do a bit more research and try anything anyone posts on here, thanks again.!!!!

 

[ramsack]

a pre-o2 exhaust leak will cause bad idle and weird running, but not in WOT.

 

[t-rexn8]

Any luck yet? I have the exact same problem on my 2G.

 

[Mr_mkelly]

I am thinking you could have a broken spring.check the spring that the lifter fell off.it could of broke 1 coil off or so...which would still seat the valve doing a compression check but float at higher rpm.a quick tell tale will be if the rocker is off again.

 

[92AWDHX40]

You say you have no tuning device.?

 

[Bluefire16]

I gave your posts a quick look, and i failed to see if you changed your plugs or at least checked the gap.

If you havent, check them, and tighten them up a bit, this is most likely the problem.