Exhaust sputtering

[CriticalB]

Last time I posted here I was looking for a Delorean, and about 3 months ago I purchased 3455, Stainless Bullet's twin turbo. So far my weekend projects have been manageable and I've found a lot of good advice here in the forums. I've replaced the passenger side window motor, rebuilt the mode switch, replaced the alternator and cleaned up some electrical connections, fixed the dome light and engine compartment light switch, recharged the AC, and replaced the injectors and plugs. She was running great after updating the alternator, until this Saturday when I noticed a line to the vacuum advance was unplugged. I plugged it back in and noticed the idle was a little smoother and the boost gauge (which hasn't moved since I bought it) now reads 20 psi of vacuum and actually responds while driving. I also noticed an intermittent sputter from the passenger side exhaust. I disconnected the vacuum again and the sputter went away. With the vacuum connected, it seems there's no sputter when the engine is cold and it comes back when it's warm.

I've been reading up on possible causes, and came across the dollar bill test. I tried it and sure enough the sputter corresponds with a sucking from the exhaust. I'm guessing this means a sticky exhaust valve at worst. I pulled the plugs, they look clean and gaps are good. Just to rule them out, I ordered some new plug wires.

I'm looking for suggestions or advice if I'm barking up the wrong tree. I'll post a video tonight. I should add that I hear the sputter at idle, but not while throttled. It's most pronounced when throttling down and when turning off the car...you can see for yourselves in the video.

Worth knowing - there are no mufflers, and the O2 sensor is not installed, so any other idle issues may be related to that. It looks like it was cut out at some point and the hole in the bung was patched. I ziptied it to the frame until I can get it repaired since it was hanging loose...I guess while I'm asking questions, is that a problem or should I just disconnect it altogether? I have an AF gauge installed as well, but I'm not sure if it's accurate...it has never moved from rich.

[CriticalB]

Here's the video:

https://youtu.be/jUMYVjIwESg

[David T]

Sounds like one cylinder is not working right. Use an infra-red temperature gauge and see which one is colder than the others. Could be a spark plug, valve adjustment, etc. Might want to do a compression test, might be a blown piston. Make sure the boost is set to under 6#. You should get the O2 sensor going and it will be quieter if you get some mufflers on it. You should also pull the outlet pipes on each turbo and see if there is any oil inside.

[Bitsyncmaster]

With forced induction, you probably need less ignition advance. Connecting the vacuum advance is giving you more total advance but in a stock PRV that should not affect idle advance since the idle switch shuts of the vacuum advance.

I would check your ignition timing with a timing light.

[FABombjoy]

Passenger side sputter may correspond to driver side vacuum issue. I can't tell exactly but also a bit of a misfire sound even at idle?

I can hear a whistle like a vacuum leak. Did you disconnect any pipes when changing plugs/injectors? The island pipes are all rough cast and a candidate for vac/boost leaks.

As to blown pistons - pull the oil cap while its running and make sure it doesn't look like Thomas the Tank engine. I doubt you have a blown piston if connecting/disconnecting a vacuum line has a direct effect on the symptoms.

[CriticalB]

Sounds like one cylinder is not working right. Use an infra-red temperature gauge and see which one is colder than the others. Could be a spark plug, valve adjustment, etc. Might want to do a compression test, might be a blown piston. Make sure the boost is set to under 6#. You should get the O2 sensor going and it will be quieter if you get some mufflers on it. You should also pull the outlet pipes on each turbo and see if there is any oil inside.

I'll warm it up tonight and check the temperatures on the exhaust manifold. I ordered a compression gauge on Amazon and will check that tomorrow when it comes in. I've been debating mufflers...it's not obnoxiously loud, but I've heard the wrong mufflers will cancel out any benefits of the turbos so I planned to spend some time researching that later this summer. I put a new O2 sensor on and dropped it in the hole where the old one was cut out just to see if it made a difference on the AF meter or in how the engine ran...it didn't. The hole just had a wide clamp around it that I removed for that little experiment. Afterwards I put some muffler tape on it for a seal and put the clamp back over that. As for oil in the turbos - I'll check it but what would that indicate?

I would check your ignition timing with a timing light.

Also ordered this from Amazon. If nothing else, owning a DeLorean has been a great excuse to fill out my workbench.

Passenger side sputter may correspond to driver side vacuum issue. I can't tell exactly but also a bit of a misfire sound even at idle?

That misfire sound is what I was referring to as sputtering and is what has me concerned. It corresponds to the exhaust sucking air in (each sputter pulls the bill toward the exhaust) However, it's way less frequent on a cold start. I just cranked it when i got home from work and it might sputter once every 10 seconds. When warm, like in the video, it does it as much as 1-2 times per second.

I can hear a whistle like a vacuum leak. Did you disconnect any pipes when changing plugs/injectors? The island pipes are all rough cast and a candidate for vac/boost leaks.

I didn't have to disconnect any pipes for the plugs and injectors. I'll inspect them, though. I hear what you're talking about in the video, but I wonder if it's not the mic picking up something that's not there. I've never noticed it in person and it doesn't seem pronounced when I listen now.

As to blown pistons - pull the oil cap while its running and make sure it doesn't look like Thomas the Tank engine.

Confirmed - no creepy train faces staring back at me

[FABombjoy]

Confirmed - no creepy train faces staring back at me

Haha, that's a good sign

If you google symptoms of "the dollar bill test" too much you might become a hypochondriac.

I think what is happening is that you have one (or more) misfires which cause gaps in the exhaust pressure waves. Then during valve overlap on an intake stroke there is exhaust reversion due to the lower than normal pressure in the exhaust. The whistling could be caused by these oddly timed pressure waves across the turbine wheel or something, that much I'm not sure about.

I would pursue spark & fuel tests before becoming concerned about valvetrain problems.

Oil in the intake would indicate failed carbon seals in the turbos. You would see evidence on the plugs (blackened/tarry ring around the ground electrode) and the inside of the intake manifold will appear bronzed. If you were misfiring and had oil I would expect to see oil in your exhaust pipes by now (oil mixed with water on cold start)

[CriticalB]

Well, ruled out spark plug wires. I got brave and decided to follow the guide to remove the whole manifold to access them. While I was in there I popped in a new distributor rotor that the previous owner never got around to installing. Took around 4 hrs and I feel like I learned a lot. Cranked right up afterwards, but idled rough and did some idle hunting. Turned it off, checked the hoses and cranked it again and this time it found its idle quickly and held steady. I could swear I heard a steady ticking from the passenger side of the engine that I didn't notice before, wondered if a plug is firing now but not combusting?

I'd have liked to spent a little more time investigating but it's late and I thought it best to let the neighbors get some sleep. The compression gauge arrived today and the timing light will be in tomorrow so I'll do some more testing tomorrow.

[DMC-81]

I'm not familiar with turbos, but aside from what's been mentioned so far, how are your exhaust gaskets and valve adjustment?

[CriticalB]

The timing light came in today and I had chance to try it out. With the vacuum advance disconnected and plugged, the timing mark lines up dead on with the 13 degree mark. It goes out of whack and the idle changes when the vacuum is plugged up and I now I think I see why.

If you recall my first post, this started when i found a loose vacuum connection and reconnected it. Now that I've studied the vacuum routing in my car vs what it's supposed to be according to the engine cover sticker, it looks like one of the PO's made some modifications. I'll try to describe how it's currently mapped, but it may make more sense if I post a diagram later.

There's a 4 port connector in the back near the CPR. One port runs to the boost gauge, one to the firewall facing side of the CPR (the outlet on the other side of the CPR is plugged), one port goes to the intake manifold. So the connection between the CPR and delay valve doesn't exist on my car. I don't even see a delay valve. The last port, which i originally found unplugged, goes to the vacuum advance.

There is no solenoid valve. I know what to look for and it's simply not there. The electrical connector is hanging loose and there is a loose vacuum hose that routes under the manifold, so I assume it goes to the thermal control valve. It was plugged with a small bolt, so I assume it was removed intentionally? Since this is a turbo setup, I don't know if I should try to get this back to the factory routing. I do have the installation guides that came with the turbos, so I'm going to comb through them tonight and see if I find anything that requires modification to this part of the vacuum system other than a port to the boost gauge. If not, I'll order a vacuum solenoid and start putting things back to spec.

There is constant vacuum in this setup, I imagine because there's no vacuum solenoid. As long as that's the case, should I just leave the vacuum advance unplugged? what would be the impact of doing that?

Lastly, i've checked when cold, warm, under throttle, etc. and there never seems to be vacuum to the 'lower' hoses in the diagram (connected to the throttle edge tapping and charcoal canister.) Does that make sense? Is it a miracle this car is even running?