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You are not going to damage anything by driving w/ DTC 26. It will not go into “limp mode” because of a single code. While driving, I doubt you will notice any difference in the performance. You just need to look at the effects on the LTFT's.
My LTFT's are still pegged very high - usually sitting at 160. Specifically BLM cell 6, 10, 11, and sometimes 18 seem to max them out.
Oddly, even with the EVAP solenoid disconnected, the duty cycle is still represented within the scan file.
The STFT's seem to be better this time around but still high - staying in the high 140s. Still not great, but it's a change.
Notably, during one consistent RPM run (had cruise control on, going 60mph, RPMs at 1750), the LT fuel trims were still pegged at 160 in BLM 10 for the duration of the jaunt.
Not sure what to try next - was thinking of maybe resetting the LT's and letting the PCM relearn again... but beyond that I'm stumped. Going to pull the spark plugs to see how fouled up they are. Engine is still running rich.
Here is the scan file, if you (or anyone else) out there would mind taking a look.
I'm starting to wonder if it could be a faulty MAP sensor, just because it seems to be fine at idle, but soon as I am driving, issues seem to arise - the various symptoms outlined by a failing MAP sensor seem to be similar to my issues, but honestly I would be just throwing parts at the void.
Last edited by tylerwerrin; 10-10-2019 at 07:37 PM.
I found a chart which indicates under what conditions the various BLM cells are active; everything in my scan seems to line up with this, which surprised me.
Could this be an exhaust leak, prior to the O2 sensors? Perhaps at the center dump of the manifolds? Is there a way to test for this without pulling it apart first? It's very crowded on the passenger side.
Cell 16 is the idle cell. You should see that LTFT any time the car is sitting still and idling.
I'm familiar with the closed loop cell boundaries and the open loop cell definitions. I have a version of that chart in my LT1 scanning guide, written in 2000, and linked in a “sticky” at the top of the “Computer Diagnostics.....” forum.
Cell 16 LTFT's not going to 160 and staying close to 128 is important, because it tends to eliminate many problems that can cause very high LTFT's - low fuel pressure, faulty O2 sensors, vacuum leaks, etc. Those things affect the LTFT's no matter whether the throttle is open or closed. Why do the 160 LTFT's only show up when the throttle is open?
Ha, yeah, once I found that diagram, it made sense why I only saw it rarely - because I was driving around, duh! I will take a look at you post now.
As for the high LTFT's when the throttle is open, I am stumped - some kind of intermittent (but predictably so) vacuum oriented issue? Or if it is a low fuel pressure issue... could there be enough pressure at idle, and under load, the pressure goes down, causing the issue?
In the last test run I did, having reset all the BLM values, I noticed that the longer I drove around, the higher the "trouble" LTFT values climbed - at first they were in the 130 range, and soon after driving for about 15-20 minutes, they had gone back to where they were in the previous scan which I had posted above.
You mention both nipples on the TB are capped. Do you use a breather to supply fresh air to the valve cover for the PCV system, rather than the stock hose from the TB to the passenger valve cover? That can throw off the LTFT's, because taking the air from in front of the throttle blades, like the stock system does, means the air that passes through the crankcase, through the PCV valve, and into the intake manifold has been measured when it passed through the MAF sensor. Hence, the PCM can add the fuel that goes with the PCV system air. With a breather, it's like a vacuum leak. Won't cause 160 LTFT's, but every bit of info is important.
A leak in the exhaust before the O2 sensors would have to occur on BOTH banks of the engine, in order to affect the LTFT's to respond almost identically. It would probably also affect the idle cell as well, although probably not to the 160 level. +/-5% on the LTFT's (122 - 134) is acceptable. Most frequent leak locations are the gasket between the head and the exhaust manifold, or loose bolts.
Good point, re: the exhaust leak. The fact that they are identical points to somewhere prior to exhaust.
As for the throttle body: There is a hose which connects the throttle body (Labeled TBU in the pic below) to valve cover on the passenger side (fresh air for the crank case I assume), and on the driver's side, the PCV valve connects to a metal pipe which then terminates to a small nipple on the front of the intake, underneath the throttle body.
Below is a picture of the passenger side - the "lower" nipple, which you can see is quite dusty. From what I recall this was part of the steam pipe system which had coolant running through the throttle body, but it was so long ago I can't remember. I think i capped it off for aesthetics as it was all rusty.
Here's the final CSV file from the ride I took after clearing the BLM's. Cell 6 seems to be the problem cell, as it's always pegged at 160; the STFTs hover in the high 140s and into the 150s.
On my 94 (which I purchased brand new) the return from the steam pipe goes directly to the radiator. The TB coolant comes from the heater return hose. On 95-97 the steam pipe return goes directly to the throttle body first. As a result, the 94 lower connection on the throttle body does not stick out straight from the side as shown in your picture. . It points outward like your photo, but after 1/2” turns 90-deg and points almost straight down.
Shoebox has diagrams of the different steam pipe/radiator hose routings:
There's a pic of my 94 throttle body lower plate here. Obviously not the stock TB, but the bottom plate (coolant connections and IAC motor) is from my original 94 TB.
Your description of the PCV vacuum hose routing also matches the 95. On a 94 the vacuum to the PCV valve is provided by a very short C-shaped hose that connects to the driver side of the intake manifold a couple inches behind and slightly above the PCV valve.
Next question..... possibly the engine is from a 95..... does your engine have a vented Optispark distributor? If so, does the vent system have the flow restrictor?
Originally, the engine came from a 93 Camaro; I wanted to use the 94/95 PCM for tuning purposes, so along with changing the PCM, I swapped out the throttle body with a 96 TB & 96 intake from a 96 Impala (along with the wiring harness of course).
While I was installing the engine into the jaguar, I swapped the 93 camshaft with a 95 Camaro camshaft and a new 95-97 style Optispark. The tune was a base tune from a 94 Camaro; I tuned out VATS and a couple other error codes, changed the tire size for speedometer purposes and changed the PCM to a manual trans. It's a bit of a Frankenstein. So to answer the 94 question - no, it's not a 94, but the tune is (mostly).
I do have the optispark hose & air limiter, currently hooked up as it should be.
On that note, I was thinking of capping the Optispark intake nipple and plugging the fresh air hole on the intake snorkle to see if that makes a difference - perhaps, to your point last night, air is being robbed from in front of the throttle blades, and if there is a leak at the optispark itself, maybe that's a contributing factor.
10-10-2019, 05:21 PM
