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View Full Version : Question for Renix Guru's with AFR experience


old_man
August 5th, 2017, 13:19
My rig has been slowly losing power and the fuel mileage has gotten down to around 12mpg. It is a 4.7L stroker and used to get 20mpg. It is not misfiring and idles real smooth.

I reconnected my AFR gauge and started monitoring how it was doing. At first I noticed that things would be good for a while then the AFR would drop to 10.0 and stay there. There was little rhyme or reason as to when it happened, other than most time is happened when I took my foot off the throttle for a second or slowed down. I replaced the O2 relay and things got better, but it still runs at 10 around town and below probably 55 mph.

In closed loop, the AFR ranges from 13.4 to around 15.

The compression is still great. I checked the coolant and intake temp sensors. Both were reading correctly. No vacuum leaks. I double checked the MAP and it's variable supply. It has a bored throttle body and I checked the TPS. The plugs look good.

Is this normal for the Renix? I don't remember this when I built my stroker 15 years ago. When yours goes closed loop, does it stay that way around town or at low speeds?

I am going to monitor the vacuum, looking for a clogged CAT and see if it tracks the readings.

I wouldn't be all that hot to fix the issue, but I have to pass a smog test soon.

Francesco
August 5th, 2017, 15:36
Interested in this as well. Just a regular Renix 4.0 here, but got 18 mpg when I first lifted it. Now I'm at 14, and it's definitely slower than it used to be. I also have a funky idle when cold, almost as if its bouncing, and sometimes it idles very high on startup. Not hijacking, just tagging along for any solutions.

comanche91
August 5th, 2017, 15:44
Did you replace the O2 sensor with a new Mopar or NGK unit? I've had similar rich A/F trouble with some of the other brands.

old_man
August 6th, 2017, 14:29
Did you replace the O2 sensor with a new Mopar or NGK unit? I've had similar rich A/F trouble with some of the other brands.

Yes I have swapped the O2. It isn't always rich. It changes in a second or two.

My question is....has anybody with an AFR gauge, seen this, and is it normal? The issue is, is it normal for the Renix to drop in and out of closed loop?

cwyman6
August 8th, 2017, 19:40
Mine drops out of closed loop on decel. I had o2 problems last year. Gave up after putting 2 new ones in. Added grounds and powers to it but to no luck. With the bad ones it would go open loop on decel and wouldn't go back to closed until i drove half a mile at constant speed. Last month i threw in another sensor for the hell of it and fixed the problem. Goes right back to closed loop within seconds of idle after coming to a stop. I suspect the heaters in the bad o2s get weak.

Im running a 90 motor in my 88 bored .020 over with 4 hole injectors

Talyn
August 8th, 2017, 19:42
What injectors are you running?

cwyman6
August 8th, 2017, 19:43
I would double check the ground and voltage for the heater at the 02 while engine is running.

old_man
August 9th, 2017, 12:05
I would double check the ground and voltage for the heater at the 02 while engine is running.Thanks for the input. I have another O2 sensor that I will try.

I am running too large of injectors for this altitude and I have built a MAP adjuster to bring voltage down to compensate. In closed loop, it controls nicely, it just drops out of lock. I have a set of smaller injectors to install if I can ever get the time.

cwyman6
August 9th, 2017, 13:20
With too large of injectors it could be cooling the 02 when it goes to open loop. Taking longer to bounce back to lean. Just a thought. Dont quote me on that.

old_man
August 9th, 2017, 13:27
The MAP sensor dials back the pulse width so the over all output is the same as a smaller injector, setting the correct AFR. It is a common technique to dial up the pulse width on vehicles with turbos. I got the AFR gauge so I could set it correctly and that is when I noticed the issue.

Talyn
August 10th, 2017, 11:07
I've seem people have problems with large injectors with renix. Even with a MAP adjuster of some sort.