Hi, I rebuilt my s4 6 port over the winter/spring (blown coolant seal on rotor 1) and its is doing several different things. I'm not sure sure whether these things are related or just happening at the same time.

Relevent mods:
KOYO rad
Junkyard e-fan (I think its from a Fiero)
T2 I/C front mounted
550cc injectors
AFC neo
PLX wideband
S4 turbo


What it is doing:

1-When I start it cold it fires up great but dies right away. It goes up to 3k for a couple seconds then drops to ~1.3k then slowly drops and stumbles to 700 and dies. Usually its fine on the 2nd or 3rd attempt, in which case it fires up to 3k, drops to 1.5k and holds until its warms up. I have it Idling at about 1k as I can't get it to idle smooth at 750rpm.

2-Driving it for any time longer than 5 minutes puts the temp guage at 1/2 to 5/8. As I am still breaking it in I'm keeping the revs under 4k. I have been checking my coolant level and it is staying right full, my overflow bottle level hasn't changed either. So either it is overheating but not enough to boil the coolant past the rad cap or my guage is reading wrong (faulty coolant sensor or something).

3-Untill it is fully warmed up (about 1/4 on the guage) my AFRs are lean (~14). If I drive it under vac/low load before its fully warmed up my AFRs go crazy lean (15-18). I have been adding fuel with the NEO but it doesn't seem to make big difference. It doesn't make sense to me that a fresh rebuild should need so much more fuel than before the rebuild so I'm suspicious of my widebands reading.

I'm going to try a new thermostat but if that doesn't do it, what could it be? I should have plenty of cooling as its a stock port block with a new koyo rad (last summer) and no a/c.

I want to upgrade to a Megasquirt but I want to make sure my engine is healthy first.

Any ideas?

 

Vacuum leak

 

1) Vacuum leak sounds about right for the idle issue.

2) Your unknown junkyard fan may just be too weak to get enough flow through the radiator. Does it cool off at speed (where the fan isn't needed)? You can try a stock fan and shroud to see if your cooling problems go away. That'd be an easy way to at least rule out the fan.

3) Assuming you have no air pump...

When are the AFRs at ~14? At idle? If so, you can adjust that with the variable resistor. Shoot for 12.5-13.0 AFR when warm. Low load cruising conditions should put you right around 14.7 AFR, since the ECU will go into closed loop and use the 02 sensor for corrections. Does it hesitate at all when you're driving? 18 AFR would definitely cause a lean hesitation if the numbers are true. It would also explain why the SAFC does nothing. You can't adjust closed loop mixtures with it.

 

Running lean will overheat your engine. A vacuum leak will cause a lean condition. Try spraying carb cleaner around the intake and listen for a change in rpm. In the future try to only make one change to your setup (this goes for basically anything) at a time. It makes trouble shooting much easier. For all we know you screwed up the rebuild...

 

Idle issues, running lean. I'm voting +1 on a vacuum leak. Did you replace all of your intake manifold gaskets?

 

All the mods were done before the rebuild and they worked then. The only thing I did at the time of the rebuild was remove the metal vacuum spider and solenoids and install silicone vac lines, so thats why a vacuum leak would make sense to me.

It is my first rebuild so I won't rule out a mistake, but I'm pretty confident that the core is good.

See above. The first place I will check for a vac leak is by the PCV valve as I've heard if that isn't hooked up right it is a vac leak.

It runs a little over 1/2 in town and a little under 1/2 on the highway, but cools right down to 1/3 after I let it idle for a bit. The fan has a bit of a shroud but it doesn't cover the entire radiator. It covers the entire top to bottom but there is about 2 inches of rad on either side of the shroud. Is that enough to cause cooling problems?

With my dads truck, when he changes t stats his "normal operating temp" on the guage will not stay the same. Like some t stats will have a slightly higher or lower operating temp. I'm just wondering if the same is true for FCs. I always hear that the needle should hang around the 1/4 mark but will using different t stats move that point around?

Like I said there is no coolant being burned or boiled over so is it possible that my guage is wrong (yes I know I need to get an aftermarket one, and I will) or the sensor is toast?

One thing I forgot to mention is that the coolant sensor in the bottom corner of the rad is not connected (I broke one of the sensor prongs). I thought it was just for emmissions though.

 

Did you port it?

 

14AFR during warm up is very lean. I'd imagine it's surging too and sounds rough?

 

It's pretty unlikely there's anything wrong with the gauge or temp sensor, but not impossible. The S4 temp gauge isn't all that bad anyway. It's actually linear unlike the S5 temp gauge which has 3 positions: cold, warm and rebuild.

1/4 of the way up on the S4 gauge is about 180F. 1/2 way is about 200F and 3/4 is about 220F. So given these numbers you're seeing coolant temps of around 190-210F, which aren't horrible, but they're on the high side of normal. The OEM thermostat isn't even fully open until about 200F (cracks at ~180F). Switching to a lower temp thermostat isn't a good idea, but testing the one you have in there is worth a shot. A pot of water with a thermometer will show you if it's opening at the correct temp. The FSM covers this test too.

Also, that temperature switch at the bottom of the radiator doesn't have to be connected, but you should connect the two wires on the harness together.

 

Ports are all stock

Thats just it, it runs smooth when its warming up, no surging. I'll check the AFRs again this weekend when I drive it. I'll have to post a vid of how it starts and runs.

So what, then, is "operating temp"? Where should the temp normally be and how much should it fluctuate, and how high should it go when driven hard?

If my narrowband O2 is toast could that be whats causing the lean condition?

 

Normal operating temp for S4: No more than a "quarter of the way up the gauge"

Normal operating temp for S5: Quarter way up to alittle below half way (yes I have seen both cases and it's normal and dependent on your cooling system). Regardless your stock gauge should NEVER go above half way, even when driving hard.

Bad narrowband will cause the car not to go into closed loop and run rich in general. I would suggest you check for vacuum leaks as that is the most common cause of running lean, even more so due to you just re-installing the engine.

 

Was this ever figured out? Having the same symptoms and my gauge goes to 1/2 in the suburbs and stays around there.