popping under boost and hard starting (long)

[at7we2]

getting *really* frustrated with my GN.

I've been trying to sort out what I *think* are ignition related problems, but I've run out of ideas. it's an '87 GN with just a few bolt-on mods.

symptoms are:

1. popping or "breaking-up" under boost at about 10 psi. it runs fine if I disconnect the wastegate and prevent the turbo from spooling up. it does this with three different coil packs, the original unit, a borrowed "good" unit, and a brand new coilpack form FullThrottle.

2. usually will not restart after it has warmed up. It will start fine when cold, but if I shut it off after it has run for several minutes, it will not restart until it has sat for about 3-5 minutes

3. when it refuses to restart, the BLM value (ScanMaster) goes to 12 or 13.

what I've done:
1. replaced coil module with brand new GM unit

2. replaced coilpack with known good used unit *then* brand new unit from FullThrottle (same symptoms with original coilpack, borrowed coilpack and new coilpack)

3. checked and tightened each pin in coil module wire harness

4. checked and tightened each pin at crank sensor wire harness and visually inspected crank sensor - looks good, tight and clean

5. pulled cam sensor cap for visual inspection. everything was clean and tight including screw holding reluctor cup.

6. I've tried two completely different chips and the symptoms persist with both.

When it will not restart I do have full fuel pressure at the rail. I don't know if this is true when it pops under boost.

The plug wires are Kirban wires with less than 500 miles on them and the plugs are AC Delco's also with less than 500 miles.

Any ideas what's going on???? (Where's that emoticon that bangs its head on a brick wall?)

Thanks for reading.

Rob

 

[NM Tom]

When you shut the car down, does the fuel pressure hold? If not, an injector or injectors could be bleeding down and flooding the engine. After a few minutes the fuel will evaporate and then start. Your break up could also be fuel related. Does the pressure rise with boost correctly? If the spark side has been checked out I would start looking at the fuel side.

 

[at7we2]

NM Tom, thanks for your reply.

that sounds logical. until now, I've been pretty confident that it was ignition related, but I will start looking at the fuel system.

Thanks,
Rob

 

[87buickracer]

popping under boost

run a leak down test to see if head gaskets is bleeding into cylinders.also check mas air flow sensor.I've experienced these similar symptoms in the past.

 

[Danster]

Rob,

By chance, did you have to clock the Turbo any to get the stock intercoolers in place? Reason I ask, because I had a popping above 10 lbs of boost and I thought it was related to the Coil Pack and Wires. After changing those two out I still had the popping. My coil pack was bad.

It turned out to be I had clocked the Turbo down too much when installing the front mount which was causing the wastegate rod to be in an angle. After I adjusted it the popping stopped.

I hope you figure it out.

Dannyo

 

[turbot2496]

getting *really* frustrated with my GN.

Actually doesn't sound like anything that serious. Not knowing a darn thing about how your problem started and knowing you have fuel pressure I would drain the tank and put some 'good gas' in the car and see if that fixes it. Bad gas will make a car do some crazy stuff. Also changing the fuel filter is cheap and might be the problem and needs to be done anyway if its been awhile. If no luck there, I would try to find someone around you that has a known good maf sensor on their car that you can swap test onto your car. Don't just run out and buy one because some are bad in the box.

Also one other free thing you can do is search really good and make sure you don't have any vacuum leaks. A leak in the line to your boost gauge for example would make you think you only had 10 pounds of boost when you actually had much more causing detonation which could be half your problem.

an injector or injectors could be bleeding down and flooding the engine. After a few minutes the fuel will evaporate and then start

This could definatly be the cause of the weird starting problem. Easy to see with your fuel pressure gauge. Good Luck.

 

[TurboBuRick]

Flat cam?

Poping under boost is a tell tale sign of a flat cam.

Pull the valve covers and inspect valvetrain. Find one not moving like the others, you found your problem.

Do you have a aftermarket vacuum/boost gauge? Bouncing needle?

 

[turbot2496]

Poping under boost is a tell tale sign of a flat cam.

If the motor isn't ticking I wouldn't sweat about this yet... possible... but I would check other things first.

 

[TurboBuRick]

If the motor isn't ticking I wouldn't sweat about this yet... possible... but I would check other things first.

Ya why not waist somemore time

 

[turbot2496]

Ya why not waist somemore time

Well, I'm a glass half full kind of guy so ..... .... to each their own though


I would guess its not the cam though at first unless its ticking. Pulling the valve covers suck compared to other things you could check first, but valve cover gaskets are cheap though so ... whatever...

 

[njbadboy]

I think your problem is fuel pressure. I had played with my fuel pressure after I installed a pressure gauge on the fuel rail that I bought from Kirban. They sell an adapter that you thread onto the shreader valve at the end of the drivers side fuel rail. Any way I put on a VDO gauge and adjusted my fuel pressure down to 30 lbs @ Idle with the vacuum line off of my pressure regulator and then drove the car. Well I could not believe how this screwed up the car. I would accelerate & at 10lbs of boost it would start to pop and surge and if I pressed further on the gas pedal it would boost to 15lbs but popped and bucked like crazy. I drove the car home adjusted the fuel pressure back to 42 lbs of fuel pressure and problem gone. The only reason I was messing with the fuel pressure is my car smells like it is running rich and I thought I would try and lower the pressure and lean it out but after this I will just live with the smell for now. I know that if I put on a catalytic converter instead of the test pipe it will get rid of the rich smelling idle but these cars need fuel and if you starve them under boost you get popping and surging. I would test your fuel system under boost and see if you are getting enough pressure. Also what kind of fuel pump are you using? You should know that these cars have bad wiring and you should upgrade to a hot wire kit like the racetronics hot wire kit and a walbro high volume fuel pump. Good Luck.

 

[TurboBuRick]

#3 exaust lobe

Drivers cover comes off easy. This where to go next.
You would not get poping from a bad fuel pump guys.

You can thank me later

 

[at7we2]

updte...

wow guys! thanks for all the posts and information! :biggrin:

cam: I won't rule that out as a possibility, *however* the popping is somewhat intermittant. it did completely dissappear one afternoon then came back the next morning. so I think that probably rules out the cam.

MAF: I'm running a T+ with a brand new GM sensor. could be a bad sensor still, but I'd be a little surprised. I'll add that to my list of things to check.

fuel filter: recently changed, but I'll probably throw another one on after I check a couple of other things. cheap and easy insurance

fuel injectors: right now I'm really thinking this may have something to do with the hard starting. I've got a fuel press. gauge taped to the windield now and I did a quick test the other night. I hit the key and watched the gauge pressurize just like it's supposed to. I started the car and everything looked fine. I shut the car off and it didn't take long for the fuel pressure to drop from about 45 psi down to about 30 psi. I'd say less than 5 minutes so that sounds like at least one leaking injector to me. My next test will be to start the car and shut off the fuel pump with the car still running. this will eliminate any pressure in the fuel rail so if the injectors are leaking it will be very minimal into the cyldiners. I'll see if it's still hard to start after doing this. From what I've read, if my injectors are in bad enough shape, that might also be causing the popping.

Another board member and local friend of mine said his car was popping because his wastegate actuator was binding. I checked my wastegate actuator and it did look like it might be binding so I'll have another one to check it with later this week.

Thanks,
Rob

 

[blackstallion]

Check fuel pressure first a bad or binding wastegate or damaged leaking vacuum hoses to the wastegate could cause popping.Also check the ground cable underneath the turbo it usaully gets loose and when he motor torques over it cause a bad connection makes eveything go out of wack.

 

[TurboBuRick]

wow guys! thanks for all the posts and information! :biggrin:

cam: I won't rule that out as a possibility, *however* the popping is somewhat intermittant. it did completely dissappear one afternoon then came back the next morning. so I think that probably rules out the cam.

MAF: I'm running a T+ with a brand new GM sensor. could be a bad sensor still, but I'd be a little surprised. I'll add that to my list of things to check.

fuel filter: recently changed, but I'll probably throw another one on after I check a couple of other things. cheap and easy insurance

fuel injectors: right now I'm really thinking this may have something to do with the hard starting. I've got a fuel press. gauge taped to the windield now and I did a quick test the other night. I hit the key and watched the gauge pressurize just like it's supposed to. I started the car and everything looked fine. I shut the car off and it didn't take long for the fuel pressure to drop from about 45 psi down to about 30 psi. I'd say less than 5 minutes so that sounds like at least one leaking injector to me. My next test will be to start the car and shut off the fuel pump with the car still running. this will eliminate any pressure in the fuel rail so if the injectors are leaking it will be very minimal into the cyldiners. I'll see if it's still hard to start after doing this. From what I've read, if my injectors are in bad enough shape, that might also be causing the popping.

Another board member and local friend of mine said his car was popping because his wastegate actuator was binding. I checked my wastegate actuator and it did look like it might be binding so I'll have another one to check it with later this week.

Thanks,
Rob

Rob, An easy test you can do, is pinching the fuel lines one at a time when you shut the motor off. There is a section of rubber hose on the fuel lines coming off the frame rail down by the power srering pump. One is feed, one is return. Choose the proper tool to pinch the lines for you don't want to cut or damage them but you need to pinch tightly. If you pinch both lines and the preasure fades, It got to be going through an injector. If not unclamp the feed line and see if the preasure fades. If it does, its the pump. I think its more than likley the check valve in the pump. Not really the end of the world.

When the poping comes on, is it a constant pop pop pop pop pop pop then goes away if you pull out a little bit. Give more detail.

 

[at7we2]

Rick87GN - thanks for your reply

when it "Pops" it continues to do so as long as I've got my foot in it. And for clarification, when I say "pop" or "popping" it really sounds like it's backfiring ( I believe the term is actually "after-firing") through the exhaust pipes. It's loud! and no, I've never let it do that for more than a couple of seconds.

the popping dissappears completely if I disconnect the wastegate actuator from the wastegate arm (zero boost).

I haven't had time to do any more testing/diagnosis - been busy with work the past week or so. I'm hoping to get back to it tomorrow (Tuesday) evening.

I'll do the fuel line clamp test (thanks for suggesting) but if it turns out to be the fuel pump, that pretty much puts me back to square one on the hard start issue.

Thanks for your input!

 

[TurboBuRick]

Rick87GN - thanks for your reply

when it "Pops" it continues to do so as long as I've got my foot in it. And for clarification, when I say "pop" or "popping" it really sounds like it's backfiring ( I believe the term is actually "after-firing") through the exhaust pipes. It's loud! and no, I've never let it do that for more than a couple of seconds.

the popping dissappears completely if I disconnect the wastegate actuator from the wastegate arm (zero boost).

I haven't had time to do any more testing/diagnosis - been busy with work the past week or so. I'm hoping to get back to it tomorrow (Tuesday) evening.

I'll do the fuel line clamp test (thanks for suggesting) but if it turns out to be the fuel pump, that pretty much puts me back to square one on the hard start issue.

Thanks for your input!

You can lead a horse to water but you can't get him to drink.
Dude, I'm only going to say it one more time. I know the sound you describe. You have a worn lobe on the cam. I gaurentee it. Put this to rest and pull your driver valve cover. Go for #3 exaust rocker. GN's are natorious for this.

Rick

 

[at7we2]

Rick,

Thanks again, but I'm aware of the cam issues with these cars. I've been there and done that also. The popping is intermittant - I think a cam problem would be consistant since a worn lobe doesn't come and go.

I've seen many other guys have the same problem and it usually turns out to be ignition related which is why I started checking those components first. Now I'm looking at the fuel system and possibly the wastegate issue.

But you have my word, after I have exhausted all other theories I will probably go ahead and drop the pan and inspect everything. (been wanting to do that anyway) If I see a wiped lobe or lobes I'll post up and say, "Yup! You were right Rick! I shoulda listened to you sooner!" :biggrin:

don't get me wrong, I'm not trying to be an ungrateful A$$, I'm just 95%...ok maybe 90% sure it's not the cam based on my own previous experiences and other local guys experiences.

I've been working some long hours lately my GN is just sitting in the garage waiting for me to find the time to contine checking all these things.

 

[TurboBuRick]

Intermittent? So your saying that car runs and boosts fine when out for a drive then all the sudded starts poping under boost?
I thought it was every time you get into boost. And don't get me wrong my friend, Im just trying to help you out. I know I can sound like a hole.

 

[mikestertwo]

Possible head gasket. Been there!!