1996 GTS: Major mixture malfunction on Interstaqte
Car has 84k and is 511 whp heads/cam/exhaust w/VEC1 MAP signal wires soldered in place (VEC1 Lambda LED indicator NOT soldered in place.)
O2's are HTK - don't know if OE. Loom connector on passenger side had a corroded pin receptacle. I soaked with white vinegar for 30 minutes, flushed with water extensively, dried, and then applied tiniest amount of dielectric grease to the male pins of the O2 connector. The driver's side look good but I still did the acid process just in case.
Startup and idle Lambda reads dead lean and no scanning. (A symptom of a bad Lambda connection is the display freezes.)
As I drive a few miles to freeway, Lambda is holding a steady mid span level and still no scanning to speak off - some slow wandering was present.
At speed on freeway, notice a "surge" like event as if 1/2 the cylinders were misfiring and then they could instantly clean up, engine was bouncing between these 2 conditions.
THEN I realized the Lambda had got Dead Rich.
All of this was at light throttle. Any attempt to get near anything mid-throttle resulted backfiring through the intake which usually is lean. If I took the VEC1 and cranked the Low adjustment to Max Rich, the backfiring would go away, but this VEC1 setting is absurd - obviously something else is going haywire.
NOTE: Before I did the "clean up" on the O2 connectors, I had identified the oxidation and had repeated disconnecting and connecting this O2. The other O2 could not be disconnected due to it's position, however I tried to press and pull it in various ways with the hope of getting some movement between the pins and receptacles. AFTER THIS, I THOUGHT THE ENGINE WAS RUNNING BETTER ALTHOUGH STILL NOT ENOUGH O2 SCANNING on the Lambda.
Even if the Lambda LED's were totally wrong, there is still something way off. I don't know if any O2 sensor malfunction to account for such extreme behavior.
Which leaves the VEC1 itself and the MAP sensor too I suppose.
I should have codes tomorrow.
And of course, I am in NV, prepping car to drive home to PA....
EDIT: I think the first thing I need to do is REMOVE the VEC1 since it is an unknown and may obfuscate what OBDII codes might be trying to tell me.
Last edited by Squid; July 9th, 2019 at 03:17 AM.
I already ordered NGK's but was not aware I could get them with longer leads. I'm assuming you're not referring to universals that have to be spliced in?
That's correct. No splice, longer length leads. I used to have the part numbers but I don't anymore. You will need to find a site like rock auto that shows diagrams of the connectors and the lead lengths. Summit racing may have pics and connector type descriptions as well.
I spliced 36" into the RHS O2 harness connector. (I could have added 6" and ran leads under frame like LHS but chose to run the wires behind the heat shield to the AC receiver, then aft around the blower motor, up to the radiator plastic tank, and then down to the engine harness.)
Just completed a test firing with DRB checking levels at idle:
Both O2 were dwelling at LOW with a periodic spike to HIGH every 5-10 seconds
After 5 min, LT trims were -5%, ST -15% (banks are within 2% of each other)
I'm thinking the O2's aren't scanning because the location at the collector is cooler. Want to give it a short test drive to confirm this. But I am a little disappointed that they don't scan at idle.
Built 1999 by TNT 511 whp, heads, cam, headers, exhaust.
RE: IAT DTC: They have the K&N down pipes angled so the ends of the K&N's are touching right behind the radiator fan - when the fan comes on, it blows hot radiator air on the K&N's - specifically the ends, one of which has the IAT installed.
I think the down pipes should be "splayed" so the K&N ends are as far apart and outboard as possible. However they drilled the nitrous nozzle ports which if oriented at 3 or 9 o-clock fix the splay angle.
Right now the ends are touching and the ports are inboard on the tubes.
If I swap tubes, the splay will be pretty good but the ports would be outboard and the plumbing will not reach.
NOTE: I can't rotate the RHS tube because the nozzle will high the serpentine idler pulley.
Perhaps since the nitrous is decomissioned, I could remove the nozzles or plumbing and get the tubes nice and splayed.
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