New SSIs in - Engine now backfires and idles rough.

[Kool-aid-82]

Interesting problems we cause ourself.
Car was running fine Yesterday. I drove it prior to installing the SSI just to have a baseline feel for sound and performance. After installing the SSI and oil lines the car does not want to idle and it backfires and sputters on acceleration, up to about 3k then it takes off.

(You can review the rebuild of Years on this thread.)
Getting my 81 911SC back on the road
SSI install Thread from yesterday. I did not change or touch any fuel system parts.
Happy 4th of July - New SSIs going in.

Following Tirwin's advice on CIS Troubleshooting for Dummies thread. (Best thread ever)

- What year is your car? 1981
- Is it a US or RoW model? US Model
- Is it the original engine or a different year engine? Original / rebuilt 3.0
- Has it been modified from stock? No
- What are your symptoms? Be as specific as possible. See above
- Did the problem start over time and get worse or did it start suddenly? See Above
- Is there anything that you do that makes the problem better or worse? Still diagnosing this
- How are the cold starts? It take some cranking and pedal play
- How are the warm starts? Good
- Do you have a pop-off valve installed in your airbox? Yes
- Tell us as much history on the car as you think is relevant See Thread above

I ran the Fuel pressure numbers today.
- WUR model? 090
Temperature for test was between 93/33 and 95/35 Fahrenheit/Celsius
Sytem Pressure = 4.9
Cold Control Pressure = 3.1
Warm Control Pressure 3.6 after 1:50 seconds
Residual Pressure
5 mins = 2.2
10 Mins = 1.9
15 Mins = 1.8
30 Mins =1.6
60 Mins 1.5

Let me know if you see any issues with this.
Would SSI cause the car to run lean?

[john walker's workshop]

what did you touch in the engine compartment?

[Kool-aid-82]

That is what I keep asking myself.
Basically the oil tank. Drained and filled.
Nothing else...

[pmax]

Are you running CIS without the Lambda system ? You can run fine with the O2 disconnected but the FV still needs to be functioning.

[tirwin]

Originally Posted by john walker's workshop

what did you touch in the engine compartment?

Agree with this. Sounds like you introduced a vacuum leak. Check the hoses near the oil filler tube. AAR hose maybe? One time I moved the AAR hose out of the way to do something. Right when I put it back on a neighbor walked up and we talked for a few minutes. I forgot to tighten the clamp. When I cranked the car it slipped off. Ran rough. Idled high. I scratched my head for a while. Retraced my steps. Bingo.

[Kool-aid-82]

Running with lambda, which worked well pre SSIs
Been checking fuel pressures and fuel ratios most if the day.
Car runs fine fine 10-15 minutes then stumbles and drops 200 rpm at idle
Fuel pressure runs constant at 3.6 bar throughout but
AF goes from 14.3 to 20/22 for a few minutes then goes back to 14.x like nothing happened.
Been thinking electrical but no luck yet.
Disconnect the WUR and thought that was it as it cleared up for a while.

I have run this with lambda connected and disconnected.
Cleaned grounds - again...

Still chasing

[gazzerr]

If the gasket is bad on the oil tank for the oil level sensor or oil tank cap it can introduce a significant vacuum leak. Does your idle drop when you remove the oil cap? If it does then you don't have a significant leak somewhere in the system.

[ClickClickBoom]

Check your CO, my ‘75 did the same thing when I took the thermal destroyers off and replaced them with SSIs and a sport muff. More airflow caused it to be way lean. Corrected it with the CO meter and never looked back.

[Kool-aid-82]

Thanks for the feedback.
I have been helping a friend get their old car running again.

It is a beast...



Got this one up and running so back to mine.

I have completed the following:
Replaced the Coil, the plugs and fuel filter (had some on the self)
Rechecked the fuel pressures. (In Spec as above) and volume (+2L per minute)
Removing the oil cap causes the engine to drop RPM. (Not the tank/vacuum)
Checked the FV Relay, (Good)




I cannot hear the FV but my hearing left years ago.

Still looking...

[Kool-aid-82]

Looks like I am computer challenged as well.
The pics that went with the above post di not want to load...

[Dave Kost]

Originally Posted by Kool-aid-82

Running with lambda, which worked well pre SSIs
Been checking fuel pressures and fuel ratios most if the day.
Car runs fine fine 10-15 minutes then stumbles and drops 200 rpm at idle
Fuel pressure runs constant at 3.6 bar throughout but
AF goes from 14.3 to 20/22 for a few minutes then goes back to 14.x like nothing happened.
Been thinking electrical but no luck yet.
Disconnect the WUR and thought that was it as it cleared up for a while.

I have run this with lambda connected and disconnected.
Cleaned grounds - again...

Still chasing

Car runs fine fine 10-15 minutes then stumbles and drops 200 rpm at idle

I've heard of the Frequency Relays go intermittently bad, which would cause the intermittent lean running condition, so I would test/replace the relay first. Any intermittent electrical issue with the ECU, O2 relay or wiring could cause lean running. Or your ECU has a bad solder join when it heats up. Check the electrical plug in the engine bay above the driver shock tower.

Also,..........
I have run this with lambda connected and disconnected.
Could you explain this statement? Are you just disconnecting the O2 sensor plug or pulling out the relay under the seat? Does the car run any differently when the Lambda System is disconnected? Please confirm.

[Dave Kost]

Originally Posted by ClickClickBoom

Check your CO, my ‘75 did the same thing when I took the thermal destroyers off and replaced them with SSIs and a sport muff. More airflow caused it to be way lean. Corrected it with the CO meter and never looked back.

Specs for our SC's ( I have an 1982), is to set the CO to .4 to .8% at 900 rpm at operating temperature. I think this is too lean if you are running ethanol gas and in Texas summers. Add to that you just put in a free -er breathing exhaust that needs more fuel, so its running even leaner now- what ClickClickBoom said.

I would start and set the CO to 2-2.5%, and see what happens. Should be easy-- you have an AF meter and it will cost you nothing.

I'm kind of curious what your AF's are at cold start. You said you do experience hard cold start at times.

Dave K

[Kool-aid-82]

Sort of... Still can't get pictures to load....
After al of the above and testing every relay in the fuel system.
Removed Cleaned and tested FV...









I started cleaning connectors, CIS box, main buss on the drives side shock tower.
Car was still running bad after 15 min warm-up.
I disconnected the Lambda (connection At Firewall) and the car perked up.

Reset AFM to 14.6, warm and adjusted idle to 925.
45 min drive this evening , Car runs amazing and has a nice sound.

Checked Lambda probe voltage @ 2500 and it is right at .6 volts.

So must be a issue in the Labda circuit.
More reading tonight I will see if it starts up in cold. ~85 degs in the Houston AM.

Thanks for all the input, it is helpful.

[Kool-aid-82]

Dave K,
I was thinking electric as well, and I guess it is an electric problem. but I guess I will have to find a non good CIS or Control box to test against the one under the passenger seat to figure that out.

I do not usually check AF mixture at startup but let the car come up to operating temps before switching out the Lambda with AF probe.

Who knew installing SSI would bring this out in the car. They really woke up the car and the gremlins.



Appreciate your help.

[Kool-aid-82]

Friends car

[Dave Kost]

Originally Posted by Kool-aid-82

Dave K,
I was thinking electric as well, and I guess it is an electric problem. but I guess I will have to find a non good CIS or Control box to test against the one under the passenger seat to figure that out.

I do not usually check AF mixture at startup but let the car come up to operating temps before switching out the Lambda with AF probe.

Who knew installing SSI would bring this out in the car. They really woke up the car and the gremlins.



Appreciate your help.

Billy thats one clean engine!

So you pulled the plug above the shock tower and the engine smoothed out. No lambda so the FV not working. Set the AF to 14.6 now it runs good.

A word on caution. The FV control the AF thru the entire rpms. My guess is that you are running too lean at the higher RPM's now. Please check that before possibly damaging your engine.

You can send your ECU out t have it inspected and/or repaired. Turnaround is about a week if you think that is the culprit.

What muffler are you running?

[Kool-aid-82]

Dave K. - Thanks for the complement, got it all cleaned up while waiting for the transmission to get back form the shop. Guess I should have spent time checking systems.

To be clear I disconnect the Lambda probe just below the Fuel filter. If I remember this should open the loop and cause the system to default to 65%

To be safe I spent today looking at the FV, and ended up chasing FV power, and it looks like my FV works when I jump it with 12 volts (hear/feel it click) but I am not getting 12 volts to the FV from the Relay under the passenger seat.
I do have power to the relay under the seat. (Man I hate electrical problems.)

I will be out of town fo work and will get back on this issue next Saturday.

[SkunkWorks]

Hey Billy, I had this happen to my 80 US SC a few years ago too (the bucking and sputtering up to 3k then fine). It was indeed my lambda ECU:

[47silver]

Did you use new exhaust gaskets on the heads to ssi’s? Leaks may cause afr to read lean

[T77911S]

you may have been on the edge of lean before putting them on. less back pressure leans it out. air leaks also lean it out.
check for exhaust leaks too