CIS Problem No. 88,763

[Porsche_monkey]

Last year I rebuilt and fired up my 2.7. At the end of the season I had driven less than 50 km on the engine. I set the timing, the cold start fuel pressures (via my adjustable WUR) and the car started nicely when cold and ran pretty well.

I went for a couple of 30 km drives earlier this year, so I'm still breaking in the engine. Last week I went to drive my car and the cold start was awful, popping and almost stalling for the first 5 minutes. So, today I tapped the WUR pin down to make my start richer, the car fires up and runs great right away. Two minutes down the road the engine is totally rich, belching black smoke, won't idle, and I barely made it back to my shop.

So, I pull the WUR pin back to where it was and drive away nicely.

The timing is very close, if not spot on. The car runs quite well warm. It is bit rough below 3,000 rpm, but pulls really well above that.

Now: I have returned the fuel pressure gage I borrowed, but I don't think fuel pressure is the problem. I don't have a sniffer to set the mixture, but when the car is warm it runs and idles nicely. Timing does not appear to be the problem. Maybe a 2.7 never runs that well below 3,000? Maybe my next cold start will be fine? Why would knocking down the pin make affect my warm pressure?

[Paulporsche]

The position of the pin seems to affect all control pressures, although the biggest effect seems to be @ cold start idle. Maybe the relationship between the cold and warm pressures is off. This can be changed by accessing yet another adjusting screw which can be found behind a brass plug on the bottom of the WUR. Before you go messing w/ that, you might want to check both your cold and warm CPs w/ the gauge.

[Porsche_monkey]

I guess I need to take it to a shop or borrow the gages again. I was hoping to avoid that, but with a CIS car I should probably buy them. (And leave them attached!)

How about the issue of 'roughness' between 1,000 and 3,000 rpm. Is this typical for CIS 2.7 or should it pull smoothly from 1,000 on up?

[Paulporsche]

My car originally had a 2.7. Other than less power, I can't recall any other difference in roughness or anything else for that matter compared w/ my 3.2, with the exception of engine temp (3.2 is a little hotter) and sound (different exhaust.

BTW how far in did you recently knock the plug? Maybe you just went too far, and you need to be between the last 2 settings?

[Porsche_monkey]

Very little. Less than 1 mm. I think I'm screwed without the gauges right now. But I have a feeling the roughness (could be too lean or too rich) almost bucking, must be pressure related.

[ianc]

Hi PBH,

The WUR does affect fuel pressures throughout the range of operating temps, not just in the cold start regime. If you've knocked the plug too far, it will make it run rich when warm.

You need to get the gauges back and verify that your cold and warm control pressures are in spec to begin diagnosis. If you set these correctly, but you're still having cold start issues, then you should take a look at the cold start valve, auxiliary air regulator, and auxiliary air valve, as they all affect either starting or cold running.

It goes without saying that everything else should be setup properly before starting this: valves adjusted properly, timing set, plugs in good condition and at the proper gap, no vacuum leaks, etc.

HTH,

ianc

[Porsche_monkey]

I'm going to tweak my WUR and get it to run well when it's warm, that's what matters in the end...

I'll update you next week as soon as the temperature here drops below 1,000 degrees C outside.

[Paulporsche]

Paul,
What do you mean by roughness? Is there any bucking between 1000 and 3000? If it bucks @ part throttle, your mixture may be too rich. If it happens @ WOT, then probably too lean.
If you want to PM me some other details, I'll let you know what I think. FWIW.
Checking the cold and warm cps would probably be your best starting point.

[Porsche_monkey]

Bucks at low RPM, espescially if I slow down and try to pull in fifth gear. I guess I need a sniffer and gauges. I was thinking about trying an emmission test shop and setting my idle mixture there.

[john walker's workshop]

did you ever set the hot idle mixture to 3.5% before you started adjusting the WUR? the bucking when hot can often be cured by removing the side vacuum hose from the WUR and plugging it. 76/77 only.

[Porsche_monkey]

No I have not set my hot idle to 3.5%, I will get that done first.

I also thought about the vacuum, but now that JW has suggested it I will be a little more less concerend about doing it.

Thanks for the suggestions, I think I need to start from scratch here...

[bigchillcar]

i second jw (always a safe bet). set mixture to 3.5% when car is at operating temperature (180 degrees). this is also the only appropriate temperature to set your 'basic idle' speed to ~ 950 rpm. from here i'd re-check my timing (static and dynamic). then i'd check my control pressures. we're assuming that the fuel pump is in good working order (not drawing too many amps), as well as the accumulator and fuel filter (new?) and no apparent vacuum leaks in the system. good luck.
ryan

[ianc]

Bucks at low RPM, espescially if I slow down and try to pull in fifth gear.

Hmmm... This isn't really a good idea. I'd say bucking was normal if you let the RPM's drop low enough. Exactly how low are you trying to pull in fifth gear?

ianc