Sorry, this is a little long. Thanks for reading.

I've replaced (literally) every sensor known to B18C, & I'm still in open loop mode. O2s reads ~0.7v consistently, a little lower on WOT.
I'm pretty sure it's a coolant system error, but I would assume someone here would know more than I would about engine management. Here's my recent findings:

ECT checks out at the sensor, 0.35 ohms (around 200 deg) at operating temp, constant 4.99v feed. However, at the ECU side I get 0.47 ohms & a feed of 2.1v... Normal? I don't get how that's possible actually. I've never been sure how to test for shorts though either.

The radiator fan Coolant temp switch (just replaced) reads ~0.7 ohm. When I remove & bridge the temp switch connector, the fan starts, but never automatically. I'm wondering if this is because the A/C was removed? (Not sure if this affects fuel control) or, if this is just due to a thermostat malfunction & why.

The upper radiator hose is always hot, lower hose is always cold. Just replaced thermostat (190 deg), not really sure if there's a way to check if it's opening or closing.

I think the ECU is not getting accurate readings & defaulting to open loop, but I'd like some help if anyone could direct me here. I'm at a loss, & too frustrated to think about it anymore. Anything is appreciated.

Thank you.

 

What ECU do you have? How far down stream is your primary o2 sensor mounted? I've seen a couple of cars where the o2 sensor simply wasn't getting hot enough even though the o2 heater was working properly.

Post more info of your setup so we know what were working with.

 

This one has a stock '94 GSR OBD1 ECU. It only has the primary O2s, mounted right after the collector before the cat.
It gets to 680 deg f, according to a local shop's records. Is there a way I can check it for myself?

Here's the mod info:

* '93 Del Sol chassis, '94 B18C1 harness & block (10:1 comp w/ lightweight pulleys & flywheel), B18C5 head (stock) adjustable cams set back to 0deg.

* 310cc injectors @ ~55psi WOT (adjustable), insulated fuel lines, stock pump.

* Custom intake manifold, medium runners / large plenum, 60mm TB. New IACv, new FITv, new MAPs, new IATs, new TPs, all vacuum components and evap system replaced (pressure @ -12psi idle), IABs system removed.

* Ported B18C1 3-2-1 headers (heat wrapped), stock cat, 3" resonator to 1.5" y-pipe dual exit (sounds like a raccoon crawled in it, for the record. Not recommended.)

* Gates timing belt, hi-flow water pump & new tensioner, stock oil pump.

* Optima Gold batt w/ ground stabilizing kit, iridium 4 plugs, 8mm wires, stock dist.

Thanks for your help

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">stock '94 GSR OBD1 ECU</TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">310cc injectors @ ~55psi WOT</TD></TR></TABLE>
you don't see a problem there? It will run ~30% rich at all times. (that's more than you think)
drop in a set of 240cc injectors or chip the P72 to control the 310s and go from there.

 

your ecu p72(stock) was design for 240cc injector.
You cannot run 310 injectors without a chip or tuning solution.
Neptune, eCtune, Hondata or Crome

 

hm. I figured with the higher compression and high-volume intake setup the 310cc would be more suitable. But I suppose my run-of-the-mill logic is a shallow match for someone that tunes ECU's.
Thanks for the input, I'll give it a shot.

 

I reinstalled the stock injectors & retried the process.
The ECU still stays in open loop regardless of engine temperature or fuel system. The O2 sensor readings are still accurate, as well as the rest of the sensors, and there are no error codes.
Any other suggestions?

 

you mentioned the bottom radiator hose staying cold. It sounds like you need bleed the cooling system.

Do you have the ability to datalog the ECT temps?

 

Not that I'm aware of, is there a way to pull logs from a stock P72?
I replaced the Thermostat again & I'm getting heated flow through the bottom radiator tube now, but still no fuel control. I tried a new ECTs and O2s just in case, but I'm still getting the same readings & mixture. I might just pony up & get an S300, I've been itching for one anyway. Thanks for your time guys.

 

Or the t-stat is bunked. I just had this happen the other day. Does it overheat?

 

no, actually i normally have problems getting it hot enough, but I just replaced the thermostat (twice).
I'm getting flow at 195 deg, and at 200 deg it's still in open loop. I'm just going to buy an S300 & program my own settings, I'm tired of messing with it - if I know what the ECU is reading it should give me a better idea of what is or is not working properly, and the ability to manually override any culprits.
I'm sure it'll pay off in the long run versus the 7mpg I'm currently burning.

 

How do you know that the factory ecu is in open loop how can you tell. What kind of fuel pump do you have and have you checked the main relay.

 

The O2s readings increase when raising fuel PSI and the injectors don't auto-correct, which would indicate it's running off the preset fuel map. It's a fairly new stock in-tank pump, I'll check the main relay for any faults & let you know.

 

You need to get, eCtune, Neptune RTP or s300.
So you can see what is going on..
Closeloop, compensate for bigger injector, coolant temp, etc etc

 

my thoughts exactly.
thanks cal, & everyone else for your help.

 

Apparently I have a short: the O2s is reading negative 0.7v --- I didn't catch the opposing polarity before. I can assume it's a bad wire or connection from a sensor.

I've never figured out how to test for this.
I have a good voltmeter and plenty of spare time, if anyone can help.

 

the only way your O2 can be producing negative voltage (it doesn't really, it simply reads negitive) is if you have the probes on the wrong way, the ground to the O2 is not actually grounded, your engine-chassis ground is poor, or if your meters ground is not on ground.

**edit** having the O2 sensor itself wired backwards may cause negative voltage...


Modified by Relic1 at 6:03 PM 6/10/2008