High-end stutter

[DynaGlide]

I'm about at my wits end on this. I've been getting a high-end stutter for some time now. When I get hard on the throttle, the engine will act like it's running rich or something; I don't even have to go WOT to make it happen. The turbo sounds like it spools smoothly, and has no shaft play. I can't notice any drop in boost via my boost gauge when it happens.

I've changed out all of my vacuum hoses with silicone hoses. I've changed my spark plugs to NGK UR5's, plug wires to Taylor Spiro Pro's, and to Conrad cap and rotor. I've changed my fuel pump to a Walbro 255 lph pump, replaced the return steel line, fuel sender, fuel tank, and fuel filter.

I am going to check the IC vacuum integrity with the bicycle tube test, and if I find nothing, I'm lost. I'm also throwing codes 33 and 34 (MAP high voltage/low vacuum; MAP low voltage/high vacuum) as well as 44 and 45 (rich and lean O2 sensor). I'm hoping that when I fix this problem, all of the codes will be remedied.

Any suggestions on what else I might replace? The coil? I still don't have DataMaster, and don't really have the money to get it right now. *sigh*

 

[sy1907]

It's hard to say without seeing the truck, but mine did something like this. Check the TB cable, making sure it's set right and the little plastic fitting is staying put when you stomp on it. Also, if you could check your afr with someone around you that may be good, not sure if your truck is properly tuned. You may have a dead spot in your tps too. Does your truck just bog down or what?

 

[InvisiBill]

Bad MAP sensor? Reading incorrect boost levels, and thus making your fueling wacky?

My old laptop's battery is trashed, but if I can get a DC adapter, I could probably meet up with you sometime to see if DM shows anything funny...

 

[DynaGlide]

I had considered the MAP sensor problem... but kind of disreguarded it until I can get everything done. Perhaps I'll get an AFR to fill my last gauge spot. I'll check the TB cable today. The only acronym I'm having a problem with is "tps"... sorry, I don't know what that is. The truck does in fact seem to bog down... that's a good way to put it.

Frusterating, this truck. I certainly appreciate the help I get from you guys though.

 

[93 TY 2185]

I had considered the MAP sensor problem... but kind of disreguarded it until I can get everything done. Perhaps I'll get an AFR to fill my last gauge spot. I'll check the TB cable today. The only acronym I'm having a problem with is "tps"... sorry, I don't know what that is. The truck does in fact seem to bog down... that's a good way to put it.

Frusterating, this truck. I certainly appreciate the help I get from you guys though.

Throttle Position Sensor

 

[Ozrein]

I'm having a similar problem. Truck runs great until I really get on it, pretty much WOT, it starts to stutter, keeps accelerating but I can hear it sputtering.

To my untrained ear, I thought perhaps a bad injector but I really dont know. One of my injectors has a loud ticking sound, so I thought perhaps that could be it.

I was thinking I'd start by giving it a tune-up with new plugs/wires, etc. (I've kind of been avoiding that because I can see it will not be a fun job to replace all the plugs) But you say your problem was the same after you replaced all that?

Sorry no help from me here but I'll be watching here to try to get some ideas, thanks guys.

 

[DynaGlide]

Well, I put the bicycle tube on the IC, and pressurized the system... I do in fact have a vacuum leak. I can hear it, but can't seem to find it by myself. The sound seems to be coming from behind the IC and intake... between them and the firewall. Anyone have any guesses as to what's leaking? It's not the MAP sensor, and I'm glad... but with my luck, it's something much more expensive.

Any guesses? Probabilities? It's a substantial leak, and doesn't leak slowly, to say the least.

Thanks.

 

[InvisiBill]

There's a major vac port at the back of the intake. It feeds EGR, MAP, FPR, vac ball, and HVAC controls I think. There are a lot places back there that could be leaking... Maybe a connection on one of your new hoses came off or loose?

 

[DynaGlide]

I'll try taking the fitting out of the intake, and plugging it with my finger to see if that is what's leaking. I'm assuming you're talking about the brass fitting at the top rear of the intake. I'll try it, give it a new coating of pipe dope, and see from there.

I've got to get these damned metal IC lines out of the way too! :lol:

 

[DynaGlide]

EGR gasket?

 

[bezerk]

EGR gasket?

that has nothing to do with the vacuumtube test..
or am i off?
just being pressuresd my the exhastgasgets right?
maybe your upper to lowerintake gasget is the problem..

 

[InvisiBill]

Yeah, I'm pretty sure the EGR gasket is just on the exhaust side of the valve.

And I was way wrong about the back port. Sorry, it's been a while since I redid my vac lines.

But there are still quite a few vac lines back there that could be causing a problem.

 

[DynaGlide]

It's the EGR valve that is leaking. I can see the diaphram inflate, but it doesn't hold any type of pressure.

Should I eliminate the EGR? What is the benefit of doing this? What would be the drawbacks? We don't have emissions testing here... so that really wouldn't be an issue. Would it screw up the cat? I don't want to cause any problems... I just want my truck to run right.

 

[kwick6]

Just take it off, and get a blockoff plate from GM #10054880, about $8.

What chip do you have? You'll set a code, but its not a big deal.

 

[DynaGlide]

Stock chip, but will upgrade to ultimate (stock injectors) when I can afford it.

 

[DynaGlide]

I should probably also note that this isn't a racing truck... it's my daily driver/stoplight warrior.

 

[kwick6]

pull the vac line off the EGR and plug it. See if that solves your problem.

If it does, then just leave the vac line plugged and get a blockoff plate.

 

[InvisiBill]

Yeah, you can just pull the vac line off and plug it with a bolt or golf tee or something to test. That's actually how I have my EGR disabled at the moment. The CEL test actually watches for a reduction in fueling due to the deadspace created by the exhaust gases, so there's no way to trick the test, short of actually changing the fueling like it expects (i.e. you can't block off the port but leave the valve hooked up or something). Depending on how you drive, you may or may not get a CEL. I've seen it maybe 5 times over a couple years. Twins says he sees it within 10 minutes of unplugging his. He says he has a really steady foot though - constant load is a requirement to trigger EGR.

EGR puts deadspace into your cylinders, so it burns less fuel. This is also supposed to keep the chambers cooler. However, the EGR process pumps nasty exhaust gases into your intake. Having crud in your intake is known to not help knock at all. The exhaust gases are also hot (duh). My MATs went from about 180°F down to 120°F just by unplugging the EGR vac line (without blocking the port off at the intake or anything like that).