Low Boost, Erratic Idle

[superbad]

Car has recently started to feel sluggish- boost is very slow to build, and caps out below 0.5 bar. In addition, idle is erratic- sometimes hovering around 1000rpm as expected, sometimes sticking up around 1500 rpm or higher, especially when coming to a stop from speed. Did an elanscan run, and the obvious stuff like coolant temp looks OK. File is attached if anyone would like to look. Note that this is at 1 mile above sea level, so ambient pressure is about 0.85 bar. It was a warm day, about 83*F, and engine was warm. You can really see how long the boost takes to build, only barely getting to 0.5 bar right as it nears 6500rpm. No fault codes. Wastegate duty cycle never goes above 0- is that because it's never making target boost, or does it indicate something else?

Vacuum leak seems kind of an obvious culprit, but I'm not seeing one. Any other ideas?

2011-06-21.zip

[saska]

You can really see how long the boost takes to build, only barely getting to 0.5 bar right as it nears 6500rpm. No fault codes. Wastegate duty cycle never goes above 0- is that because it's never making target boost, or does it indicate something else?

Think it's because you're not making target boost.

Vacuum leak seems kind of an obvious culprit, but I'm not seeing one. Any other ideas?

I agree vacuum leak is the most obvious candidate. You may want to rig up something similar to JonT's ingenious test rig see HERE
If you setup the test rig, connect elanscan, switch on ignition (BUT DON'T START), Start Talking (F1) on Elanscan, you should be able to read 'Boost & Manifold Press' generated by the test rig and then listen around the vacuum hoses for the hiss. A small tube and funnel can make narrowing down the culprit easier. A diagram of the hoses is HERE
Other notes:
1. Idle was too high at 1175
2. Spark advance at idle was 8.4 degrees and while I know this isn't the same as base timing (16) my experience is that a normal scan will show 15-20 deg at idle. Think I'd check base timing.
3. There are 4 knock events and 3 were severe enough to retard timing 1-1.5 deg
4. Were you going downhill at 100 secs ? Power was 220hp and acceleration 1.2g, both of which would be pretty impressive on the flat.

[superbad]

Yeah, I agree, I'll try pressurizing the intake manifold and see what I can find.

1.2g longitudinal would be astonishing in any FWD car, let alone a stock Elan not making full boost. No hills, but that acceleration channel is derived from wheel speed (I think), so probably just a sensor malfunction. Wasn't getting wheelspin, and definitely wasn't accelerating anywhere near that hard.

[superbad]

Frustrating evening. I can't get any significant pressure into the system with the innertube rig, but I only have a little hand bike tire pump. The innertube inflates and holds some pressure for a while, it just doesn't move the boost gauge. If I pump furiously, I can get enough to detect some hissing that sounds like it's internal around the throttle. One of them was in bad shape, so I replaced all the vacuum lines off the manifold (to the reservoir, EGR solenoid, evap emissions solenoid, secondary, boost gauge). With the engine idling, if I pull off a hose I get a jump in idle. However, I don't get the little vacuum hiss when moving the heater control, and I can't see the secondary throttle moving. If I idle the engine with the intake hose removed (the one from the wheelarch pipe to the throttle body), there is a very loud hiss from the IAC port. Is that normal?

Pretty much stumped.

[JonT]

I think you're unlikely to get much registering on the boost gauge using the inner tube - with a twin piston car foot pump and SWMBO sat in the drivers seat, she could see it just about getting up to 0.2 bar when I was pumping frantically (remember I'm also suffering a boost leak). At the risk of sounding patronising (and I don't mean to be) - I assume you did have the ignition turned on while trying to check the gauge?

The hissing I can hear is also from around the throttle body area - like you I went through changing lots of lines and hose clips and still didn't resolve it. What I did notice was pushing/moving the top of the EGR slightly caused a change in hiss. I'm planning to pull the EGR off this weekend and see if that's the underlying cause. Saska's suggestion of a funnel and small tube was quite helpful in trying to narrow down where the leak was coming from.

The other trick I mentioned on my thread about the issue but forgot to put on the wiki page is to get a squirty bottle/plant mister and fill with water + generous amount of washing up liquid. If you spray this liberally around the hoses, any pin-hole leaks should produce bubbles making the culprit easier to find.

[superbad]

Jon- do your other vacuum functions work, like the heater controls?

I am kind of leaning against this being a vacuum leak. With the system pressurized, if I pull off a vac hose, there is a rush of air, and the whole thing instantly deflates. That means that whatever leak exists (if any) is much smaller than that. The intake manifold is not really airtight with the engine off- some air will go past the throttle and down into the pistons, one of which will have some valve overlap that allows air down the exhaust. Anyway, the turbo should move enough air to swamp small leaks.

[JonT]

Yes, heater controls work fine. Like you, under the test conditions pulling off a hose immediately deflates everything. I take your point about a slight leak always going to be present into the engine, but I don't think you should be able to hear a hiss - implying escaping to atmosphere.

[superbad]

My idle was much better today after swapping all those lines, but the boost is just about non-existent. I think if you were to drive around with a vacuum line unhooked, it would still generate decent boost, especially at higher revs.

My cat has had a rattle for a few weeks, I'm wondering if the substrate isn't all blocked up now. Really high backpressure would show symptoms like these.

[tigerdog]

Actually I was going to ask about that. If it sounds like someone is shaking gravel in a pan when the exhaust vibrates, that's your issue. If the substrate has fractured, it rotates so the teeny passages no longer align and exhaust cannot flow. Huge backpressure! Same symptoms as Smaug and at least one other recently. Since you're not in California, you have the option of choosing among many different standard and high-flow cat options. See? It's an opportunity to improve performance!

[superbad]

Yep, that was it. So much better. I had got used to the wheezy, low boost configuration, so getting it back the way it should be makes it feel like it's been chipped.

[tigerdog]

Must be a Fed Elan thing. One more item to add to the "watch list".

[DeanG]

I've had both the interior of the muffler and the catalatic converter let go on me.

The first time it was the interior of the muffler at the Zippo Vintage GP at Watkins Glenn. Monday was the Lotus only track day. When the junk in the muffler restricted the exhaust there was very little power. A bit of a bump and the power came back. The most memorable was going up the S curves. The car made horrible noises. People behind me were pulling into the pits to check their cars!

While chasing an intermitant fuel injector I had 2 catalatic converters die. One smelled bad and the other one had turned into honeycomb chunks.