OK, so here's a new one...low idle, help me please!, also timing questions Options

[porsche735]

We just finished rebuilding our engine and it started right up the first time...

We set the timing at 27 degrees with both hoses removed at 3500 rpm. After the engine had warmed up and the aux air valve shut (even tested by plugging air inlet to valve), we tried to set the idle.

The idle is way too low, about 500 rpm max. The adjustment screw is making almost no difference. I played with the mixture screw on the ECU both directions (refresh my understanding, it is backwards, right? CCW is leaner, CW is richer). Adjusting this did not make a huge difference. I adjusted this to achieve highest rpm and richened one click (CW).

We cleaned out the air bypass hole to make sure it was not plugged.

We also played around with the TPS by shutting the butterfly valve all the way to make sure the ECU "thought" it was in idle mode.

I also have another question about advance. I have been told that we should see a total advance (with hoses on) of around 33-34 degrees. We checked our's after setting the 27 degrees the normal way, it was around 39 degrees. Does anyone have any specs on the mechanical advance and vacuum advance (retard as well, I guess)? My understanding is that at WOT that vacuum advance should be close to nil. We should basically only see the mechanical advance. However, we are seeing about 12 degrees advance due to the vacuum advance (39-27=12). Does this make sense?

We played with the advance all over the place and were not able to get the idle to go higher.

Please help me with these questions.... Your help is much appreciated.

Chris

[Brad Roberts]

Is it running on all 4 ?? I mean firing on all 4 ??

Sounds like a dead cylinder or two to me..

Or was it very smooth ??

Correct: unless you have the vacuum advance line hooked up to the wrong spot on the throttle body... it should have almost NO vacuum at WOT.


B

[Bleyseng]

Sounds like you have the vacuum/retard hoses hooked up wrong- switched. The vacuum advance hooks up to the port that is above the throttle plate. The retard hooks up to the lower port.
The air bleed should increase the idle cuz it adds air into the engine bypassing the throttle plate. Only if the timing is off have I seen this, so recheck the timing. ie-if you add air to the engine rpm should increase right? something is goofy here.
Make sure the marks are the right ones (use the Pelican tech article for the template)
27 degrees BTDC @ 3500 rpms with hoses off and plugged (means take them off the dizzy and plug em)
Geoff (IMG:style_emoticons/default/confused24.gif)

[porsche735]

It's running on all 4. This is very odd. The timing marks are correct. We checked that true TDC measured at the 0 mark on the fan. We also did our own math and found the same 27 degree mark at 2.05", so our marks are correct. I just don't get it. The hoses are hooked up correctly. Same as before and re-verified with Dave's pictures on the PP web pages.

What else should we check?

Thanks,
Chris

[Brad Roberts]

Did you wash the engine compartment with the pressure sensor hanging on the wall ??

B

[porsche735]

No, why? They don't work when filled with water?

Serioulsy, this should have no effect at idle anyway, if I understand things correctly.

Chris

[p914]

How long did you let the engine run before trying to set the idle? Check the thread on PP bbs ECU Knob Adjustment and see Brads posts.

[porsche735]

It ran maybe 10 minutes. We did not run it hard as it is a fresh engine. I waited for the aux-air valve to close and then, to be sure, closed off the air inlet to it. This all shouldn't be an issue. the bleed screw does not seem to do much, fully closed stalls it, but barely open to full open is essentially no change....

chris

[redshift]

As Dave said over on PBird, cam break-in @ 2000 rpm for 20 minutes (non-detergent oil) change oil, then wait a day, and adjust your valves.

Have you done that? Tight valves, I am wondering?

If the valves were tight, that would be mechanical cause for what you are seeing, and it sounds like you have done the right 'other stuff'..



M

[porsche735]

It is just a top end rebuild including P&C. However, we still did the 2k for 20min. thing. When we adjusted the valves outside the car, we adjusted them, spun the engine about 5 times, and then re-checked and readjsuted a few.. The valves should be pretty close... We will definitely re-adjust before we run this weekend at Laguna Seca...

chris

[p914]

I think a bit more time to warm up is needed. Let it get to a good running temp. Redshift has a good point re:valves.

[porsche735]

It is not the temp of the engine. In general, the idle goes down with increasing engine temp. In this case, my problem would get worse....;-(. For the quick and dirty, letting it warm up enough to close the aux-air valve and then shutting off the airflow to it should be pretty good.
One thing I thought of. With the throttle body gasket, do you all make sure the drilled channel for the air bypass is covered? Ours is.

Chris

[redshift]

I am wondering if we aren't on the wrong end looking at this. What kind of fuel pressure are you getting?

You just did a topend redo, injectors changed lately?

If you add air, it adds gas, unless it can't.

Have you seen our mascot? Could be fur in the lines.

(IMG:style_emoticons/default/wink.gif)

Was there a thread about this engine, including the specs? I wonder if you have a mismatched part.



M

[porsche735]

The parts are matched fine. The engine was working on most cylinders before we pulled it out..;-) I can check for kinked hoses, etc. But, we have run the car and it runs well. It is just the idle that is goofy. The fuel pressure is at 29 psi. I can raise it a little, but adjusting the mixture screw on the ECU should change it at idle.
I don't have any furry friends around my house except for some squirrels and skunks. Neither of which make it into my garage very often... Notice, I did not say never.;-)
Injectors were flowed and rechecked just bit ago. We can pull them and check the pattern, but I suspect they are OK.
There is probably some dumb-ass thing we have done. I just can't figure it out. Maybe reflecting on the relative intelligence of my buttocks.

Chris

[redshift]

lol.. hang in there Chris.

When it was running, it didn't sound unbelieveably smooth? No?

I'm thinking....


Miles

[porsche735]

Unbelievably smooth, yes. We cced the heads and matched the compression. It runs beautifully. Almost no vibrations.. Just won't idle about 600 rpm.....

Chris

[ChrisReale]

Is the idle bad at all operating temps? Double check timing and the TPS. Those have bit me in the ass a few times whe I thought I was being thorough.

[p914]

With the throttle body gasket, do you all make sure the drilled channel for the air bypass is covered?  Ours is.

Chris

That I have not checked. I discoed the smog pump on mine as in WA state any vehicle over 25 yrs old needs no emission inspection. I also use a K&N and do have the AAR hooked up. Although, I may try experimenting with it by plugging it also. PBAnders probably has the best experience along with Bleyseng that I am familiar with. I have tried a number of settings on mine before and after my mechanic tuned and adjusted things. The daily temperature and humidity do have effects and when a seasonal change sets in I usually adjust my system.. Are you working in a closed environment or an open garage?

[porsche735]

Chris,
Yes, pretty much any temp. I did have some problems with the TPS before in trying to get it adjusted right for throttle closed 0 ohms. Even though we have replaced our's once, it looked pretty worn (but OK) last time I opened it up (about 4 months ago). We only track the car, so miles are hard, but not many. How long do your TPS last? I thought they should last for quite a while.
My test of this is to short out the TPS conductors to simulate the closed throttle position. This should force the ECU into idle mode. That way, at least, I can take that out of the equation.

Chris

[Brad Roberts]

Did you find anything Chris ?? I'll be in Palo Alto tomorrow and will need a break away from what I'm doing around the time you get home. I can shoot down San Antonio and make a house call. I need to see this.

I have had this problem in the past... just dont recall the solution.



B