83 sc backfires won't run help please

[Laneco]

At this point in time, don't worry about the one hole with lower compression. Pretty common if they sit for a while to have a bit of carbon trapped between the valve and seat.

When you've got things sorted, just drive it. Most likely, it will clean itself out with a good long run. Not drastically low anyway, should it decide to stay right there.

Regarding the airbox, whether you repair this one, or replace it, make sure it has a pop-off valve.

angela

[mreid]

Originally Posted by timmy2

Need one of these for your lambda male pins?
I just started casting them. Couple of air bubbles in the first one, but the next ones will be better. Completely functional though...
Send me a PM if interested .

Dennis, this is fantastic! What's your price point?

[timmy2]

$20 shipped conus seems reasonable to me.

[roadster49]

Update: New airbox installed. New connector installed from Timmy 2. Connector was perfect replacement. Took some cranking to get started with a few exhaust backfires. Adjusted timing and idle to spec. Added a quart of oil when warm with engine running and the idle changed with the oil cap off but kept running As part of the repair I tightened all head studs, adjusted the valves, and reset the lash from the 1.4 to the higher end of the scale 1.7. I also put a new relay at the brain

When warm it runs beautiful

When cold bucks and hesitates terribly

I could not get an O2 reading from the exhaust as the level was very low. Note that the PO had drilled out the plug.

So I am happy it fired up but disappointed in cold performance. It takes about 4 miles before it runs good again

I will retest my pressures and report. Help please.

Michael

[roadster49]

Maybe not a cis issue. Could it be the coil as it backfires a lot now?

[roadster49]

Update: checked WUR resistance. It was 26.4 ohms , outside temp 53 degrees. The frequency valve vibrates with fuel pump on and engine off. Checking fuse 18 looked old so I replaced, and do have lamp working over glove box. Replaced the relay at the control unit. Engine runs horrible now both cold and warm. When I get back this weekend I will test pressures again and go back to the beginning. Question, how do you check the lambda control Unit. What am I missing

[timmy2]

Suggestion:
After checking all fuel pressures are in spec...
Check the "brain" board for solder cracks with really good magnification. Hi res camera blown up works well.

[boyt911sc]

Michael,

Get the engine to operating temperature and hook up a dwell meter using the test port. And the check the OXS voltage. Two things you have to check:
1). That the OXS is transmitting voltage reading to the ECU. Use a volt meter.
2). That the ECU is in good working condition. I don't know how to test and evaluate an ECU. I have several good ECU units that I use for the test to compare with the questionable ECU.

Until you have confirmed that these two critical parts are good and working, troubleshooting your problem would be quite difficult.

Could you do this test for me? Please measure the WUR resistance (Ohms) when the engine has reached or close to operating temperature. Or after 10 and 15 mins. from a cold start. You have to unplug the WUR electrical connector to be able to measure the resistance. A 10 min. and 15 min. interval would be my interest. Thanks.

Tony

[roadster49]

Tony and Tim. Thanks will do Friday when I am back

[roadster49]

Another day in analysis:

Checked WUR. 26.4 ohms. Outside temperature 49 degrees

Fuel pressure system - 6.6 bar
Fuel pressure controlled- 4.5 Bar
WUR connected - @ 2 minutes - 5.4 Bar
4 minutes - 5.5 Bar
5 minutes - 5.6 Bar
10 minutes- 5.6 Bar and WUR 9.4 ohms

Checked perma tune and all resistance levels were within spec
O2 sensor readings were 0 before start and was able to see exhaust readings fluctuate with engine running

Pulled #5 plug, it was light grey in color

Cleaned 14 pin connectors and perma tune connectors
Installed a spare coil
FV vibrates
It started, grumbled and backfired a flame out the exhaust.
As it warmed up still grumbled and rough with occasional backfire

Got it to run but shudders and misses bad on acceleration

Adjusted air and idle and was able to get it to run a bit better at low Rpms
Surges high low at idle
Runs strongest when warmed up and high Rpms
Overal poor drivability

So any next steps or recommendations welcome

[Bob Kontak]

Originally Posted by roadster49

So any next steps or recommendations welcome

You control pressure is absurdly high.

Hook up with Tony and send him your WUR. He will calibrate.

Your poor car is "out of gas" it's so lean.

Let me find the graph and post.

[Bob Kontak]

You system pressure is too high as well.

[roadster49]

Hi Bob,
Got a call into Tony
Hope that's it! It is driving me nuts

[boyt911sc]

Michael,

I was in the garage working all day testing and calibrating a dozen WUR's and was a very frustrating day. Got only three (3) WUR's to pass QC tests and stopped working pass midnight. I missed your phone calls and left a message.

Your fuel pressures are out of wack!!!!! How did you mess up the fuel pressures? Have you been tinkering the WUR and FD? Both your WUR and FD need to be calibrated if not rebuild. I am quite busy these days testing CIS components and finishing two (2) engine rebuilds side by side. But I will find some time to look at your WUR and FD.

Tony

[boyt911sc]

Originally Posted by Bob Kontak

You system pressure is too high as well.

Bob,

Michael's car is an '83 SC USA model and has a WUR-090. The control fuel pressure chart you provided is for the Euro or RoW cars with WUR-089 that is vacuum assisted unlike the WUR's used with the lambda type 911.

And I completely agree in your observation about the very lean condition. With those fuel pressure readings, I doubt if you could make the engine run well even after a very long warm up. Both the WUR and FD need to be calibrated for the engine to run smoothly and efficiently.

Tony

[Bob Kontak]

Originally Posted by boyt911sc

Bob,

Michael's car is an '83 SC USA model and has a WUR-090. The control fuel pressure chart you provided is for the Euro or RoW cars with WUR-089 that is vacuum assisted unlike the WUR's used with the lambda type 911.

You are correct, as usual, Oh great WUR Guru. It was late and I was painting fenders all day. All I can think is it's a fume related mistake. (or beer?)

Another thing I was thinking is, can the high system pressure bump the control pressures up by default? Maybe something is incorrect upstream? Off spec fuel pump?

I just replaced my original fuel pump from my 81. Guess what? My front end damage messed with the gauge and I was only out of gas. My original fuel pump is old but functional and sitting in a box in Ohio still waiting to serve......

[boyt911sc]

Originally Posted by roadster49

Another day in analysis:

Checked WUR. 26.4 ohms. Outside temperature 49 degrees

Fuel pressure system - 6.6 bar
Fuel pressure controlled- 4.5 Bar
WUR connected - @ 2 minutes - 5.4 Bar
4 minutes - 5.5 Bar
5 minutes - 5.6 Bar
10 minutes- 5.6 Bar and WUR 9.4 ohms

So any next steps or recommendations welcome

Michael,

I woke up in the middle of the night (actually very early morning) thinking about these data. These could not be right unless your pressure gauge is defective but I doubt it. Check your fuel line return. There is a flow restriction between the FD and the fuel tank. Keep us posted.

Tony

[roadster49]

Tony,Bob,
I will recheck my procedure and numbers later today and post.
Michael

Tony,
I have my phone ringer on high so I don't miss your call

[Bob Kontak]

Originally Posted by boyt911sc

There is a flow restriction between the FD and the fuel tank.

Tony,

I don't think this is the issue. If you had complete blockage, control pressure, at worst, would be equal to system pressure. That is not the case.

System pressure is too high.

All ears though. Just thinking, not arguing.

Here is the correct graph:

[boyt911sc]

Originally Posted by Bob Kontak

Tony,

I don't think this is the issue. If you had complete blockage, control pressure, at worst, would be equal to system pressure. That is not the case.

System pressure is too high.

All ears though. Just thinking, not arguing.

Here is the correct graph:

Bob,

Did I say 'complete blockage'? I said flow restriction some where along the the return line (just kidding because I'm in a good mood right now and not grumpy). And I agree with you with all my heart that the system pressure is ridiculously too high. And you could be correct. The very high system fuel pressure could be caused by the actual primary valve setting or a flow restriction some where along the return line. The fact is we don't know. We need to test and confirm.

So I spoke to Michael about this problem and discussed the next step to diagnose the culprit/s. Let's wait for his test results and hopefully it would give us a better picture of the situation. My initial reaction was the gauge could be bad or defective and that's another thing we have to know.

An example of cold control pressure test reading @ 38°F (early this morning):


And the system fuel pressure test reading:


I have another gauge but using three (3) gauges in tandem is over-kill. One (1) good gauge is more than sufficient DIYers would need.

Tony