Ispeed

Running Lomas X (no cats) with small resonators and rmb. (VS stock cats and rmb.)

My S4 is running warmer than with stock exhaust, as seen on the temp guage and an infrared heat sensor. At idle it's 210f leaving block and 185f returning. Car runs GREAT, but temp guage will vary and go close to last white line when it didn't do that before. Fans are more active as well.
After brainstorming with Dave C, we came up with a few possible reasons:
1. car is running leaner with lower back pressure exhaust. I know that it should be able to compensate, but probably it can't.
2. Old mass air sensor maybe not up to the task of keeping mixture correct.
3. Bosch +4 platinum plugs may make car run hotter also, will try oem plugs.
4. Injectors need to be ultrasonically cleaned (?), have already run LOTS of Techron through it.
5. Possible sharktuner tuning of the LH to make it look for a different oxygen level to make it's mixture adjustments. Meaning the lower backpressure confuses the LH in the ways that it makes it's mixture changes, so maybe we need to adjust the LH some.

New stuff: radiator, 75c thermostat, wires, coolant, and everything else under the hood.

Anybody have some other ideas or experience?
Thanks.

RDS928S

I have Motorsport X with no cats and new o2 sensor & platinum 4 plugs. Otherwise stock exhaust and it runs within range.


Rich

worf928

Do you have temperature measurements?

IIRC the temp leaving the crossover should be 180 to 195 degrees F.

ROG100

No change in temp with the GTS.
Just going to put the X on my 87 and will let you know.
Roger

tv

1 and 2 are very possible. I have read before that those plugs do run hotter, try a cooler rated normal plug. I use a japanese one with the split prong. Does your car have the plug near the LH to retard your ignition 3 degrees? Try that for experiment.

New radiator and coolant, do you need to burp it? How new is this exhaust? Also maybe you broke a sensor when fiddling and is the t-stat pointing up?

Ed MD

No change in my temps in either car, with cats and without. Check your your AF ratio, removing the CATS did lean out the results a bit when I dynoed the 85, but not enough to evenwant to change the AFR and then again these are high flow CATs. Make sure you gauge is correct, I had a problem with the 944 running hot recently and changed everything from sensor to thermostat ( a major PITA on a 944) to flushing the system to new hoses..... once I replaced the battery because of a dead cell the gauge worked fine and it was were it used to be. Make sure that your data, i.e. you gauge is correct and that your not chasing electrical ghosts. Ed

danglerb

Global warming is more likely a cause than the new exhaust. Check the sensor, the A/F, and the cooling system.

worf928

Carl's not reading off the gauge. The temps are from an external IR temperature tool and measured at the coolant crossover elbow. The motor's running 10 to 15 degrees hotter than it should.

We could always pull the plugs and read them.

Ispeed

We might try one thing at a time to see what helps: cooler plugs, rebuilt MAS, new 83c thermostat, new water pump, etc.
Like I said, the car runs great, but I'm wondering how it will do in 90+f summer weather. Gotta be ready for SITM weather!!
"Owning a 928 is like not waiting for fire, but looking for smoke and fixing it then."

worf928

One thing we can do is throw your cats on and see if, with the higher backpressure, the car runs cooler. That's the quickest way I can think of to rule out (or in) the low back pressure causes lean(er) running.

Ispeed

I hate cats!!! But I'll do it!

jon928se

1. If the LH is being fed the correct data it shouldn't make any difference.

2. Quite possibly - on a non cat equiped car ie without 02 Sensor an aging MAF can produce a lean condition - which would make it run hotter

3. Don't think so. the plugs them selves could appear to be running hot but not the engine. +4 platinum not recommended for S4 - use Bosch WR7DC or Beru ????or NGK BPR6ES normal plugs.

4. possibly but the LH should be able tocope if you have a properly working 02 sensor and MAF

5. shouldn't be neccesary but I doubt that you have upped the performance sufficently to take it outside the range of the LH's ability.

O2 sensor and MAF would be the first things I'ld check, but to be on the safe side and to avoid wild goose chases before that I'ld check the T stat and maybe the waterpump, and make sure the plastic bits between the front PU and the radiator are all secure not able to move and obscure the airflow.

marton

I would start with the thermostat; cheapest and easiest-to-install option.

How old is the MAF? Was the main reason you put on the modded exhaust to improve the performance or because you like the sound? If it was for performance and if you have an old MAF in that is losing you 20/25 HP then you should consider to change the MAF anyway.

Marton

Mrmerlin

Hi How old is the O2 sensor? since you replaced the X pipe you have moved the O2 sensor and possibly damaged it, or the wiring to it since the O2 runs up on top of the old header it is easy to cut or otherwise damage one of the O2 wires. I would get another O2 and swap it into the pipe it is pretty easy to do, Change plugs and lastly change the thermostate, By the way there is no burping necessary on a 928 since the system is self bleeding (it has an outlet on the front of the engine and on top of the radiator and these hoses both return to the resivour tank). With the exception of filling the heater core this can be done after filling the system and letting it reach temp then going fo a 5 mile drive with the heater core opened, after returning check the system and fill to the half way mark on the resivour

Ispeed

I have been suspecting the MAS is the weakest link because so much other stuff is new, and I know that they age and cause lean running. I have no paperwork that shows the MAS was ever replaced, and I have records back to almost new. And it is getting older all the time, maybe it's ready to be rebuilt now.
I was very careful installing the 02 sensor in the X pipe and routing the wires, and it was new in '05.
I want to go back to an 83c thermostat from what I've heard you run hotter with a 75c tstat.
p.s. the X pipe is a performance upgrade, and the car runs stronger for sure. I have dynoed before and will dyno again soon.