I had some issues w/ my 88 iroc, the old ECM was shot, it was putting the iac in pos 160 causing stupid high idle. Swapping the ECM w/ the one from my 87 fixed that. Engine runs so much smoother, idles down and has the required cold start high idle. The old ECM wouldn't even run properly in 10K and field service mode. In field service it would run pig rich but the iac would come down, in 10K mode it would stick rich, not as rich as in field service but enough to trigger a rich flag over time. The lockup would get funky also, not engaging sometimes.

Anyway, I swapped the ECM and all is fine except for one thing. As soon as the ECM sees a distributor ref. pulse the fan comes on. Not w/ the ign on.

I checked it w/ TTL Datamaster and there's a bit that says "Fan ON disabled by PID" and it's set to 1. I checked some other logs and they're always off (0 or a green field)

What is PID? Prom ID?? What gives? This never happened on the 87. I'm 99.999% sure the dr. side fan worked as it should on that one but maybe it never came on at all, maybe it was shot. I'll have to check that.

Any ideas? Is there something out there that sets the fan on all the time like a hypercrap chip???

Forgot to add, ECM registers CTS just fine, everything else is fine too...no issues whatsoever..only the damned fan.

 

no one??

 

Guess no one has this issue?

My problem is, the BLM and INT read a little high, INT around 130 and BLM about 132 and it's causing me to fail emissions w/ 1% CO (and a whole bunch of HC ppm but it's not a reason for failing but it does indicate a problem)

O2 is around 1.1 so there's unburnt O2 left.

I thought I had it fixed w/ the air diverter valves. Clamping off the dr. side to the headers dropped the IAC to 114 while BLM was still stuck @ 136 but the low INT eventually for that down to 132-131. Now after swapping the vavles and checking wether air pumps to the headers (it doesn't the old one did) I figured I had it fixed. Now, BLM and INT are both on the rich side and the stupid fan is still running.

Somehow there's unburnt fuel in the system, my last thing I can think of is welding a 2nd O2 sensor in the pass side and then seeing if there's a problem there and see if the ECM controls it better if that side is monitored. Any ideas?

 

BTW, fuel pressure is fine. O2 sensor is new, cross counts are fine, O2 swings run/lean just fine. Can't find any air leaks, no exhaust leak.

 

Did you use the same memcal when swapping ECM?

 

Oh....I dont think the BLM is the issue its only showing how much correction the ECM is doing (how far the stock calibration is) according to the O2 sensor. Check you timing? bad cat?

 

used the one from the 87 camaro, swapped it completely. Both are L98 (5.7) automatics. Same ecm & memcal.

Timing is set 6*, correctly. CAT should not affect CO, should be able to get well below .5 without it.

BLM shows that ECM is seeing and has been seeing a slight lean signal for some time. BLM used to be as high as 138 before fixing diverter. Then INT was 114-120 correcting for the BLM effect. Brought BLM down to 132 and it's stuck there now w/ INT also 128-132. It's running too rich that's why I fail emissions. AF @ 14.2 instead of 14.7

In other words, the ECM is correcting for a lean making it too rich. The lean condition is false but the O2 swings fine, no excessive hanging on the lean side.

The only thing i can think of is maybe an injector issue on the other bank causing the CO and the BLM & INT from the drivers side bank are actually pretty good and the other bank, not being monitored, is screwing up my exhaust emissions. That's why I hate 2-1-2 systems. If I install new cars I'm welding up true duals. At least you can monitor if it's bank specific or a condition similar on both sides.

 

Change the O2 swing points some i PROM ?

 

It's a bone stock car, don't think there's a need to plug the ostrich in this one and do some tinkering. Should be able to run just fine. It has a N10 dual cat con system, the rest is bone stock. Car drives silky smooth, idles silky smooth...no issues apart from fan & CO. Target AFR according to TTL = 14.74 @ IDLe

Another thing, why is it that w/ a laptop and a prog like TTL datamaster & aldl/usb cable I have to jumper into 10K mode to get date. However, when I plug in my red brick scanner the idle stays steady @ 650, not elevated to 1K like in 10K mode. Seems to me like it's spitting out serial data to the red brick even in normal (open) mode.. what gives? Same ECM in 87 vette also spits out serial data in open mode on notebook/TTL Datamaster.

 

10k mode will only send out data in 160baud, 10k is needed for 8192baud.

 

open mode only 160 baud? W/ WINALDL it will spit out only basic data?? How does my red brick get all the int, blm, cross counts and whatever else data there is then?

 

cant tell without seen it, but you get all the data at 160baud just not at the same speed..........

 

weird, I get no data in winaldl and in tts datamaster without the 10K mode (jumpered aldl cable from aldlcable.com, has jumper for open, 10K & field service)