car runs rough when it gets up to operating temp

sniperdude wrote:

Saw this older post from Eldo.

Quote :

There is just the one temperature sensor that feeds the PCM, then the PCM sends serial data to the IPC 'brain', which decodes it and actuates the gauge motor.

yeah I just wasn't sure if that was for the '95s as well. Should be but that doesn't always mean it is.

Not exactly sure how to interpret the data.

If anyone wants to have a crack at it: http://www.2shared.com/file/7OfX2fnD/riviera_scan1.html

I had to use $5B ECU def files - http://www.tunerpro.net/download/bindefs/GM/5B_TPV5.xdf and http://www.tunerpro.net/download/datastreams/GM/5B_V5.adx

The temp sensor looks good, it increases linearly the longer the car has been on, so that makes sense.

I just scrolled through this thread briefly.

#1 I'm appalled at that work order from the dealer. It's bullshit. They didn't diagnose a damn thing. That pisses me off sooooo bad!!!! It makes people like me look bad.

#2 Has anyone mentioned the Fuel Pressure Regulator? If it has a small hole in it, it would definitely run worse as the car warmed up. Simple check....pull the vacuum line off of it and see if there's fuel in the hose, or leaking out. It's quite common.

#3 The Trans Range Selector on the dash. Usually, when that happens, and all the flashing happens, the transmission range switch (located on the transmission) is bad. This could also cause some driveability concerns as the PCM may not exactly know which selection you have the shifter in, and defaults to "safe" mode.

Without seeing the car, I can't help all that much. I can only go by what's here....

Thanks, Scott. That's some solid info.

I was really pissed at the lack of info as well.

They told me I should be grateful because "Not many dealers would do a compression check"

One thing I noticed last night when I was running the scan was that if I pushed the brake pedal down hard, the idle fell down and almost stalled. Is it possible that the vacuum booster is leaking causing the bad idle?

I'm basically guessing at this point. Lol

Absolutely man. A leaking brake booster will kill every bit of engine vacuum and make the car want to, if not stall. Take a look at the booster hose...it goes DIRECTLY to the intake. I'd definitely look into that some more. If you have a vacuum pump, do a simple leak test right at the booster.

No vacuum = car runs like chit

Yeah because I also noticed last week after I changed my brakes, the pedal takes a lot of effort to stop the car. This combined with the idle drop makes me suspect of the booster for sure.

Would any of these issues cause that #4 cylinder low compression issue?

No. I don't think I'd be TOO concerned about that at this point. I'd get that vacuum leak (if that's what it is) fixed first. That will/should cure the idle and surging problems. You can worry about anything else after the fact.

I just thought of this. With the car in Park, disconnect the booster hose. Stick a bolt or something in it to stop the leak. If you're confident enough that you can stop the car, and it's going to be tough, go for a ride and see how it runs.

Do I disconnect the engine side?

sniperdude wrote:

Do I disconnect the engine side?

NO!!!! Disconnect it right at the booster, and block the line off. It should stop the vacuum leak to the engine. However, it will render the power brakes useless, and be VERY hard to stop. I'm talking white knuckles and 2 feet on the brake pedal.

Engine side is going to try to be pulling a vaccum so you would need to plug it. If you pull the booster side and plug the hose going to the engine you are taking the brake booster out of the equation.(Which can tell if its leaking or not.

Note of caution, when Scott says it will be hard to stop the car he means it!

Edit.. yup Scott got to this first.

Cool, just wanted to make sure.

I can usually get the idle issue to happen just by idling the car up to the 200F temp.

Definitely gonna check this out.

sniperdude wrote:

Thanks, Scott. That's some solid info.

I was really pissed at the lack of info as well.

They told me I should be grateful because "Not many dealers would do a compression check"

One thing I noticed last night when I was running the scan was that if I pushed the brake pedal down hard, the idle fell down and almost stalled. Is it possible that the vacuum booster is leaking causing the bad idle?

I'm basically guessing at this point. Lol

I'm guessing that in the future you need different dealer.

Boy was i nearly clueless on this one... Thanks Abaddon

Albertj

OK, so I tested this out this morning.

I drove it around for 10 minutes, got it up to 200F temp on the gauge, shitty idle started up.

I noticed that pushing on the brake pedal makes a strange noise. Like a suction noise. (brake booster hose still connected) I took a video of it, you can hear the sound when I pump the brakes: https://www.youtube.com/watch?v=GTx742tkq0I&feature=youtu.be


After disconnecting the brake booster hose, I noticed there was no *whoosh* noise, like the vacuum escaping. On every car I've worked on, when disconnecting the vac hose for the booster, there's usually a noise when the vacuum escapes.

I plugged the vacuum hose at the brake booster side with some plastic sheeting and a 10mm socket, and it did make a noticeable difference. The idle was still kinda bad, but nowhere near as bad as it usually is. I suspect there are other vacuum leaks, or other issues to chase down. The exhaust smells pretty rich.

I also noticed that the port the brake booster hose connected to was wobbly. That might be where its leaking from.

this is interesting. I've been told that a Dual master cylinder set up will give you the same pedal power that a brake booster does.Eliminating the brake booster would simplify things.Anyone care to comment on that?

If the diaphragm in the booster has a hole in it, it will make a wind noise when you push the pedal. If it was leaking from the check valve going into the booster (or the grommet as you describe as wobbly), you would most certainly hear a loud hiss from it when the engine is running.

If the car ran better with the hose disconnected and plugged, I think you can possibly rely on the booster, the grommet, or even the check valve (very rare) to be bad.
That hose and the booster are a HUGE potential vacuum leak, asm it's connected directly to the intake...

Glad you're back, Scott!

If I wanted to do a vacuum test, on what hose does the tester go into?

I was looking at picking this up: http://www.harborfreight.com/fuel-pump-and-vacuum-tester-93547.html

What kind of readings should I be getting in park, neutral, or drive?

I'm not sure "we" are ready to vacuum test anything right now. Everything we're talking about can be eliminated easily.

Make sure everything is connected and plugged in.
Start the car.
Let it run for a few and build vacuum.
Shut it off.
Let the car sit for about 5 minutes.
Get out, and pull the Brake Booster hose off of the booster itself. It should make a giant sucking noise when you remove it. If it doesn't, you have a leak either in the booster, the check valve, the hose, or the grommet.
If you find that it doesn't go "whoosh" when you take off the hose, next you can verify the check valve operation.
It works much like a PCV valve. You can blow air through one way (with some force), but cannot blow air through the other direction. If you can pass air through both ends, the check valve is bad.
(FYI, the check valve is the 90* plastic piece that connects the hose to the booster)

By all means, if you feel the need for a vacuum tester, buy it. But I can tell you now, that it's not something used very often. Broken or leaking vacuum lines and/or gaskets can be found quite easily with a $5 can of Brake Clean. We'll get into that later if need be. Right now, I think you should just figure out if the booster is bad or not.

Edit: You can also find vacuum leaks using a 2 foot piece of hose as a stethoscope. Stick the hose in your ear, and follow around the vacuum system. You'll definitely know if/when you find a leak, as it will hiss quite loudly in your ear.

I also forgot to add that if the booster is leaking internally, then with the car running and the brakes applied, you may hear the hissing or sucking noise from under the dash. Good way to hear that is the good 'ol fasioned way of sticking your head down there and listening.

Awesome, thanks for the info. I'll try and take a better look at it later.

When you say "(FYI, the check valve is the 90* plastic piece that connects the hose to the ball means"

Is the check valve in the brake booster connector which you attach the hose to?

sniperdude wrote:

When you say "(FYI, the check valve is the 90* plastic piece that connects the hose to the ball means"

Is the check valve in the brake booster connector which you attach the hose to?

That's what I meant haha. Stupid fingers. I've edited it to be correct

No problem, man. Can that be removed?

Yes. It's just held on by a barbed end. The hose will come off. Maybe not easily, but it will come off.

Actually, a vacuum gauge is an excellent diagnostic tool. IMHO, it should be in every mechanics tool box. I use it all the time, but I realize that late model engines with ECM and fuel injection have less use for a vacuum gauge. You can still diagnose valve and ring problems. In any case, a stock 3800 should pull 20" of vacuum fully warm and in Park. Any less than that and you have a leak somewhere, or other problems. My boost gauge is actually partly a vacuum gauge.