7747 Won't Enter Closed Loop At Idle

[brian617]

Fan temp switch should be in head or intake crossover, similar to the CTS and Temp gauge sender. It will be easier for fans to regulate the temp you ask for if it samples the same area gauge and CTS sample.

[1project2many]

OE fan on temp for many apps is around 224 and off around 221. I think I'd go with higher temps on yours.

The average O2 voltage is still close to stoich but that may be inconclusive. The O2 change in the exhaust would be small.

Good luck. I think you're going to get this figured out.

[SBAdam]

Thanks, I think the suggestions are going to make the difference. Here is what I am planning to do:
1. Switch cal file to 91 CA emissions config
2. Replace tstat with 195F
3. Relocate fan temp switch to engine and change to 210 or higher
Anyone have a recommendation for a temperature switch that will thread into one of the unused ports? The fan setup is 2-speed, so I would like to have low/high dual element.

[SBAdam]

SOLVED (sort of)

I still don't know why the ECM isn't going into closed loop at idle, but when I increased the physical idle setpoint to 900rpm, I was able to force the ECM into closed loop. 900rpm is above the max engine speed for open loop and below the upper limit for the CA low speed idle smog test (1100rpm). This is a bit of a hack job, but actually the engine starts and runs better with the higher idle speed even as the fans turn on and off. AND, with the ECM solidly in closed loop, I breezed through the smog test: CO% went from 1.2 to 0.0.

I did replace the t-stat with new 195F, I also switched to the 91 CA emissions BCC, which should be better overall, though it didn't change the closed loop behavior at idle. Haven't changed my fan temp switch location yet - now that I passed the referee inspection I am eager to start driving the cruiser and enjoying the fruit of 2-1/2 years of labor.

I may revisit this issue down the road, since I haven't really solved the root cause. It would be great to have the engine start and idle smooth at 650rpm as GM intended, but for now this solution is good enough. If anyone has questions just send me a message or continue the thread - this forum was a great help and I would be glad to return the favor.

Thanks!
Adam

[tayto]

did you ever install a heated 02 sensor? i had an '89 Caprice when I first started learning about fuel injection 15 years ago. I discovered after many years of owning that it would drop in and out of closed loop at idle and light cruise. factory o2 in factory location (drivers exhaust manifold).Now, it could have just been a faulty/old 1 wire sensor, but when I replaced with a 3 wire heated o2, it no longer dropped in and out of closed loop.It also got into closed loop faster.

[SBAdam]

Tayto - that is really interesting. Others suggested similar, but without the specific experience you had. If I try the heated O2 sensor I will be sure to report back.
Thanks

[tayto]

it wont hurt anything is especially if you haven't replaced the o2 sensor yet. i buy 3 terminal weatherpack connectors from auto part store. unpin your original single wire connector and run ground and ign+ to the other terminals. good luck

[brian617]

Have you tried changing any of the parameters in the .bin for closed loop idle? Most of those early 7747 where open loop idle. The Heated o2 will help, but only if the parameters in the .bin are set for closed loop idle.

[PlayingWithTBI]

it wont hurt anything is especially if you haven't replaced the o2 sensor yet. i buy 3 terminal weatherpack connectors from auto part store. unpin your original single wire connector and run ground and ign+ to the other terminals. good luck

I found these on Amazon. The 3 wire adapter is pretty much plug and play, just needs a switched power source.
https://www.amazon.com/ACDelco-AFS74...1275051&sr=8-3

https://www.amazon.com/Michigan-Moto.../dp/B0141VHZ6U

[tayto]

that's a nice way to go. i normally find the ground and ign+ junctions (usually a big crimp) in the engine harness and tie in there.

[SBAdam]

I purchased the heated O2 sensor and will be installing in the next week or so. Will report back on results. Thanks for the info.
@Brian617 I have not modified the BIN yet, but I expect I will go down that road eventually. If you have specific tuning advice or experience relative to closed loop idle I would appreciate any guidance. I have the software just not the hardware interface (yet).

[SBAdam]

Installed heated O2 sensor, no change in open loop idle. I think this configuration just doesn’t do closed loop idle. Thanks for everyone who contributed. If I dig into tuning the bin I will reach out to the experts in the community.
Adam

[brian617]

That is correct, a lot of those early .Bins are open loop idle. Only a modified .Bin will change that.