Warm Startup Issues

[knodeland]

Scratching my head about recent warm start issue on my 82 SC with Lambda CIS. Starts perfectly from cold - high idle that comes down after the engine warms. Runs like a top - smooth and sounds great. I can drive it around from cold through full operating temp and the car runs like a dream. However, if I park the car for 10 mins (e.g. stopping to pick up groceries), it starts hard and runs lean (lots of exhaust popping) for the next 5 mins before it settles back into smooth running at operating temp. There are no vacuum leaks - just had it tested on a smoke machine. Any ideas?

[Bob Kontak]

Originally Posted by knodeland

Any ideas?

When warm, CIS holds pressure in the lines from the fuel pump to the injector tips for an hour or more. This allows the car to start without the rich mixture and cold start valve spraying in extra fuel like on cold start.

Guessing you have a leak that bleeds off residual pressure.

Once started though, I can't understand why it would take 5 minutes to bring all back up to pressure and run smooth (assuming this is the solo issue)

Others are smarter than me. Just be patient and know that you will be prompted to buy fuel pressure gauges. $125.

[ossiblue]

Originally Posted by Bob Kontak

When warm, CIS holds pressure in the lines from the fuel pump to the injector tips for an hour or more. This allows the car to start without the rich mixture and cold start valve spraying in extra fuel like on cold start.

Guessing you have a leak that bleeds off residual pressure.

Once started though, I can't understand why it would take 5 minutes to bring all back up to pressure and run smooth (assuming this is the solo issue)

Others are smarter than me. Just be patient and know that you will be prompted to buy fuel pressure gauges. $125.

Bob's nailed it^^. That would have been my exact response.

Now, buy a fuel pressure gauge set, run the complete set of pressure tests, and report the results (do a search, or ask here, if you need to know how to do the tests.) We really cannot help without test results.

As far as the 5 min. it takes to run smoothly, that could be a separate issue (weak fuel pump, eg.) or just a misperception of the length of time. Regardless, one step at a time, so take care of the hard start first.

[knodeland]

Thanks. I replaced the fuel pump check valve and accumulator several months ago, which solved my hard warm start issue. This new issue is strange - the engine fires right up when warm, it just runs with lumpy low idle for 5 mins or so until it gets back to perfect running. Other than the lumpy idle, the car can drive and it doesn't hesitate much - there is just a ton of exhaust popping when I come off the throttle. Then suddenly its great again. Very odd. I'll pick up some gauges.

[Bob Kontak]

Originally Posted by knodeland

Thanks. I replaced the fuel pump check valve and accumulator several months ago, which solved my hard warm start issue. This new issue is strange - the engine fires right up when warm, it just runs with lumpy low idle for 5 mins or so until it gets back to perfect running. Other than the lumpy idle, the car can drive and it doesn't hesitate much - there is just a ton of exhaust popping when I come off the throttle. Then suddenly its great again. Very odd. I'll pick up some gauges.

Based on this info it does not sound like a residual pressure issue is a primary culprit.

Although, it could add to the symptom equation.

I would focus on the Lambda system as well as pressure test. Test is pretty easy. Time but not hard.

Replace the relay cube under the passenger seat, connected to the Lambda box. You can test it but for a few bucks just change it out.

Disconnect and examine the 12 pin connector towards the middle of the car on the back rail to the right (from rear forward view-point) from the drivers side shock absorber. Clean off any crusty stuff on the male pins. Spread them open a tiny bit with a blade and "bore" the female ports out with a wire brush or some kind of mild scraping tool. Just get any crud or patina deposits off, to aid connection. Nothing earth shattering. Just shake it up a bit.

Spread the pins on the red fuel pump relay a pinch, also.

[boyt911sc]

Originally Posted by knodeland

Scratching my head about recent warm start issue on my 82 SC with Lambda CIS. Starts perfectly from cold - high idle that comes down after the engine warms. Runs like a top - smooth and sounds great. I can drive it around from cold through full operating temp and the car runs like a dream. However, if I park the car for 10 mins (e.g. stopping to pick up groceries), it starts hard and runs lean (lots of exhaust popping) for the next 5 mins before it settles back into smooth running at operating temp. There are no vacuum leaks - just had it tested on a smoke machine. Any ideas?

knodeland,

Without knowing your fuel pressures, it would be difficult to assess the root cause of your problem/s. Next time you have the motor completely warmed up, do the oil cap test. I am curious about your air/vacuum leak. How well do you know who did the test? Smoke test is a good way to locate air leak/s but does not do well with the CIS air box unless you have the engine out of the car. There are several critical spots behind the CIS airbox that you don't have a good view. You maybe be correct that you don't have an air leak and that's good.

But when I read your post, two (2) things come to my attention:
a). Fuel pressures (control, residual, and system).
b). Unmetered air.

Where both the fuel accumulator and FP check valve tested and verified defective? Or you simply replaced them? Keep us posted.

Tony

[Bob Kontak]

Originally Posted by boyt911sc

But when I read your post, two (2) things come to my attention:
a). Fuel pressures (control, residual, and system).
b). Unmetered air.

Good input.

Only reason I stress the Lambda relay and connection clean up is because it is free AND OP mentioned backfires.

[boyt911sc]

Originally Posted by Bob Kontak

Good input.

Only reason I stress the Lambda relay and connection clean up is because it is free AND OP mentioned backfires.

Bob,

That's my other point. But since you mentioned it, I did not emphasized on it anymore. There could be other culprits that we have not mentioned. Checking the most likely suspects is our common or usual way to to diagnose these problems but sometimes it is something not obvious or apparent to us.

Tony