Suddering Under Boost

[9!'clipseDOHC]

My freshly rebuilt 1991 4G63T engine shudders hard under boost. At about 3K rpms with about 8lbs of boost it starts shuddering, sputtering, and refuses to accelerate. At first I thought it was the fuel pump because I still had the non-turbo fuel pump but I just installed a Walbro 255lph and a Buschur/SX AFPR set at 38psi with the vacuum line off and it is still doing the same thing. I don't know what else to check. Also the "check engine light" is on saying something like "Fuel pump or control relay". It said that with the non-turbo pump and still with the walbro/SX setup. When I let off of the accelerator so that there is no boost or just like 3lbs it runs fine but it’s a piece of crap with boost. I was better off, faster, and had a lot more money with the non-turbo. I don't understand.

 

[9!'clipseDOHC]

Nevermind I found out that it is a boost leak. I disabled the turbo by undoing the wastegate arm and it runs perfect, it feels faster than it did as a non-turbo but that dosent make much sense because it basicly is non-turbo now. Tomorrow I will make a leak tester and find out where it is. I think that it is on the intake manifolr or the throttle body because I can hear air from that direction when I rev it up. I am so glad that I figured this out because this car was making me depressed.

 

[TJGoSurf]

I may be wrong but if you undid the wastegate arm wouldnt that mean you are boosting all the time?

 

[92awddsm]

I may be wrong but if you undid the wastegate arm wouldnt that mean you are boosting all the time?

No, it means that you are build little to no boost all the time because the wg stay open all the time.

Anyway, Ive got a leak tester if you need to use it. Glad to see you got it back together. Unfortunately, you still have problems. Welcome to the turbo dsm world.

 

[4g63t]

glad to see your figuring it out now boost leak was my guess as well check all the manifold and turbo gaskets they are sneaky some times!

 

[9!'clipseDOHC]

Oh Yeah, The turbo DSM world. I'm definitely in it up to my neck but I'm not yet reaping the benefits of turbo dsm speed and power. I went to home depot today to make a boost leak detector but one of the pieces that I got was wrong so I will try again tomorrow. Thanks for the offer of using your leak detector and if the one I'm making doesn't work out I will take you up on your offer. Thanks for your help. I'll let you know how it goes with my leak tester and if it fixes the problem.

 

[9!'clipseDOHC]

I made my leak tester and sure enough there is a bad leak where the throttle body bolts to the intake manifold. I'm going to replace the gasket tomorrow and test again.

 

[92awddsm]

I made my leak tester and sure enough there is a bad leak where the throttle body bolts to the intake manifold. I'm going to replace the gasket tomorrow and test again.

Forget the gasket. Just go to advace and get some pematex ultra gray rtv and never worry about it again.

 

[9!'clipseDOHC]

Forget the gasket. Just go to advace and get some pematex ultra gray rtv and never worry about it again.

Will the rtv hold better than a gasket? If it will than I will do that and forget the gasket.

 

[92awddsm]

Will the rtv hold better than a gasket? If it will than I will do that and forget the gasket.

Yes it will.

 

[xcz504d]

Post how well your fix action works, Im curious to see if that resolved your problem.

 

[AnkurJ0217]

I think i have the same exact problem....i just bought this eclipse GST a week ago..its a 99'...well...the car runs fine with building boost up until around 3k rpms then the car just shakes as the rpms vary rapidly not wanting to go past 3000 rpms. Also i hear this puffing sound..then some ticking sounds if i do it too much. I cant even floor. I basically drive like grandma and would like to know if a Boost Leak is the problem? Can you help me determine whether the symptoms i describe are the symptoms of a boost leak? the check engine light is on also. The car also over heats at times...no clue why.

 

[xcz504d]

Ankur, I think you should start with flushing your coolant system and replace your temp sensor, you don't want your car to over heat, the turbo gets hot enough when it's running properly.

Check your plugs and plug wires you might want to change them anyway, if they are the stock plugs and wires they are over half a decade old! Your plugs can tell you whether your running to rich or to lean, not very accurate but can give you a good idea of what might be the problem.

After you get the general maintenance stuff out of the way, it makes it easier to put blame on a specific part.

DISCLAIMER! This can cause damage to your engine if you are not careful! If you build full boost and one of your pistons isn't igniting it you can cause a detonation!!! There are safer ways to test for leaks! I suggest getting a leak tester.

Can you driv eyour car in third gear slowly over 3000 RPM? if so, take it a little over 4000 rpm (assuming you have the stock turbo) and give it a little gas to build boost, make a mental note of how high the boost built before it studdered.

Try the same thing on the highway but in fourth gear and floor it (flooring it in 4th wont take you much past the speed limit) and see if your car builds full boost while stuttering.

4000 rpms should be enough to build full boost on 3 cylinders, depending on the size of your turbo.

If you build full boost in 4th gear starting at over 4000 RPM's and the boost holds steady, you can assume boost leak isnt your problem.

DISCLAIMER! This can cause damage to your engine if you are not careful! If you build full boost and one of your pistons isn't igniting it you can cause a detonation!!! There are safer ways to test for leaks! I suggest getting a leak tester.

 

[9!'clipseDOHC]

I think my car hates me. I fixed the leak between the TB and manifold and it boosted just fine. I got my boost controller set to 15lbs and it felt good and strong. I went to make a pull and after 2nd or 3rd it lost all boost and power. It felt very sluggish and sounded very strange. I got it home and checked under the hood with it still running. The wastegate had come off (I hadn't put the cotter pin back in yet) which explained the lack of boost but not how slow it was. My car sounded fine at idle but when I hit the throttle it sounded like an electric motor, like a grinding or growl I don’t know its had to explain but it doesn’t sound good at all. I noticed smoke in the engine compartment and I shut my car off. I looked under the car and found the wire to the factory oil pressure gauge (the thing that looks like a bell) hanging down not connected. I hooked it back up but my autometer pressure gauge read good the whole time. I check the oil and it was full, and I looked and there was oil in the head. I hooked up the wastegate and started the car after it had cooled down and it still had that horrible growl/grind and there was white smoke come out the exhaust so I shut it off. Now what? I’ve only got a little over 200 miles on this rebuilt engine.

 

[xcz504d]

Draing your oil, check for metal...

Does it grind/growl in nuetral when you rev? Or when there is load (in gear)?

What year was the motor manufactured?

Who rebuilt it? I would definately have the guy who built it have a look, unless that would be you. Check piston compression... Is it coming from the engine or transmission?

Top or bottom of the engine?

Could be your input gear bearing if its coming from the transmission or close to it.

Grinding in the engine block is not good at all...

White smoke could be alot of things, with lack of power and white smoke I would start with a compression check of your pistons though.

 

[9!'clipseDOHC]

Draing your oil, check for metal...

Does it grind/growl in nuetral when you rev? Or when there is load (in gear)?

What year was the motor manufactured?

Who rebuilt it? I would definately have the guy who built it have a look, unless that would be you. Check piston compression... Is it coming from the engine or transmission?

Top or bottom of the engine?

Could be your input gear bearing if its coming from the transmission or close to it.

Grinding in the engine block is not good at all...

White smoke could be alot of things, with lack of power and white smoke I would start with a compression check of your pistons though.

It sound ok in neutral it only makes the noise when I rev it, I’m not driving it right now. I can’t tell if it’s coming from the top or bottom but its not coming from the transmission. The engine is out of a 1991 Plymouth Laser rs turbo, it was rebuilt first by a machine shop but apparently they didn't clean out the ring glands because the rings froze to the pistons and I had no compression. Then it was fixed at a local import shop and the rings were replaced and everything was cleaned. I will have to borrow a compression gauge but I will definitely check the compression and I will also drain my oil and see what it looks like.

 

[xcz504d]

Usually after a rebuild you want to take it easy on the engine for the first 500 miles or so to let everything settle into place. It's not un-common to see a little bit of metal the first time you change the oil after a complete rebuild. Thats just part of everything fitting together again while the gaskets seat into place and what not. But there shouldn't be enough metal to cause a grinding sound unless somthing broke.

I wold start with a compression check, just because that was the problem area before the rebuild.

You can pick up a compression gauge pretty cheap at an auto store if you can't find one to buy. Get a Haynes manual while your at it if you don't already have one, it will giv eyou more insight as to what the different readings mean, worn piston rings, blown head gasket, valves springs, and that sort of thing. Make sure you have a little bit of oil handy when you do the compression check too, you'll want to put a teaspoon of oil in the piston for a second test.

 

[9!'clipseDOHC]

Compression is 130, 130, 105, 100. Cylinder 4 i rechecked and it went from 100 to 60. I'm going to try another gauge because the one I was using wasn't holding, the pressure was slowly dropping and I'm not sure if it is the gauge or the engine.