Oddball Update

This past weekend, I finally got KITT’s fuel injector swap squared away. The car had been running 24 lb/hr Accel fuel injectors (installed by previous owner just before I bought it) which was causing a rich air/fuel mixture, as the computer was still expecting stock 22 lb/hr units. Ordered some Bosch 22s and got them installed. The intake was a damn mess of funky screws, stripped threads and gnarled bolt heads.

Anyway, now that that’s done, I no longer stink like gasoline every time I get out of the car. Presumably this also means I’m not getting severe fuel leakdown into my cylinders, and my fuel mileage won’t be so bad (haven’t driven enough to tell yet). The car is also smoother at the low end of the powerband, whereas before it was choking on fuel and would bog pretty embarrassingly up to about 40 miles an hour at light throttle.

However, I find that I am still having certain problems. After doing a lot of research into the possible causes and remedies, and since I have a lot of “volatile” information floating around in my head right now, I figured I’d come by here and make a big list to myself of what I know so far and what I plan to do. This won’t really mean much to most of my readers, but it can be fun to eavesdrop on people’s projects, so here we go. I will discuss the symptoms, causes and remedies for one problem at a time.

Problem #1: Low-RPM Bogging

I had this problem before the injector swap, and attributed it to the car choking on excess fuel. That appears to have been correct to some degree, as the effects have lessened with the new injectors, but they are definitely still there. What happens is that the car is bogging (stumbling) at low RPMs. Whether you pull the throttle linkage from the throttle body or step lightly on the accelerator, the engine stumbles and misses right up until 1500 RPMs, when it suddenly purrs smooth as a kitten up through the remainder of the powerband. It does this both in park/neutral and in gear, and it does it all the time—when the engine’s just been started cold, and when it’s been hot and running for a while.

Since it bogs both cold and hot, this takes most of the sensors out of play, including the oxygen sensor. The reason is because when the engine is first started, the ECM is in “open loop” mode and disregards input from almost all of its sensors until the engine coolant reaches a predetermined level. The only sensors it cares about are the coolant temperature (CTS) and the engine oil pressure (because if oil pressure drops too low while starting, the fuel pump will be automatically shut off). The CTS is important because when it is reading cold, the ECM will inject more fuel into the cylinders. So if your CTS has failed, the ECM will see a negative reading and will constantly add fuel to the mixture. As a result, you’ll be running pig rich. But that doesn’t appear to be my problem—I’m pretty sure I’m not running rich anymore.

What else could it be? Likely culprits include fouled spark plugs, a dirty/faulty Idle Air Control valve (IAC) or a misadjusted/faulty Throttle Position Sensor (TPS). Additionally, the throttle blades or IAC inlet passages in the throttle body could be carboned up pretty bad and not admitting good air when they are partially open. It might also be the EGR valve or solenoid. Or the MAF sensor. Or a vacuum leak. Or possibly even a clogged fuel filter, or a faulty injector. I’m mentally ruling out the last two for now, since the fuel filter is pretty new, and obviously, the injectors are brand new.

So as you can see, I’ve got a wide range of things to check out. The problem? I can do hardly any of them because I don’t have decent tools. I need a torque wrench to properly reinstall the IAC stepper motor if I remove it, for example. I need a digital multimeter to check and modify the TPS adjustment. I need a host of Torx bits to do much of anything. It’s all a bit frustrating.

I’ve decided that the first order of business will be to pull a couple of spark plugs and check their condition. Since I was running pretty rich for a while, they could be fouled pretty bad. If I’m getting poor spark, it just might explain these problems. I’m also leaning toward this answer because when I first inspected and test-drove the car in Ohio, it did not bog or stumble at low RPMs because I certainly would have noticed. That suggests that the problem has been getting worse over time. Since the condition of the spark plugs has definitely been getting worse since I bought the car, this is the most likely suspect.

But again I run into this tool problem. Changing the spark plugs on the L98 TPI engine is an absolute bitch from hell. You need deep sockets, right-angle sockets, etc. etc…some people even say they prefer to change the #8 cylinder plug from underneath the car. I’d hate to have to take my car to a shop just to have $40 worth of plugs changed—I’d feel like such a goit—but what else can I do? Fortunately, 3/4ths of the plugs are easy to remove, so I can at least pull a couple and check their condition. I can tell visually whether or not they are likely to be causing my problem. After checking & replacing the plugs if need be, if the bogging isn’t cured, it’ll be time to crack open the throttle body and IAC valve and clean ‘em out.

Problem #2: Longer Cranking Time Required Before Ignition

This problem did not occur before my injector swap. Now, each engine start—whether cold or hot—takes a good two seconds of cranking before ignition. The car always cranked real funny before the injector swap—sometimes it would crank fast, sometimes it would churn slowly, other times it would even modulate different cranking speeds as it was turning over! But when the engine was warm, it never took long to fire up. Now, it always takes a good couple of seconds to turn over, even if I’ve just turned the key off. But at the same time, it also cranks good and fast and never sounds like it’s croaking or getting “stuck” like it used to. Problem? Well, not really, because it never fails to start. But it makes me wonder if it’s getting enough fuel. Of course, if I’m correct about my spark problem mentioned above, then that could be a factor in this as well!

Problem #3: Engine Stalls Repeatedly After Cold Start

This one troubles me more. This, again, is something the car did not do before the injector swap. If I let it sit for a long time—overnight always works—when when I come out to start it, it’ll do the usual two seconds of good, fast cranking, fire right up as usual, then…as the RPMs settle down, they’ll keep settling…the tach will sink…the engine will sputter and stall. Usually takes all of about two seconds to die after ignition. So you’ll start it back up, give it a little throttle this time. It’ll rev fine as long as you’ve got the throttle open, but let go and it’ll probably die again. You’ll mess with this for a few moments, then suddenly it’ll “catch”—the RPMs will hold at around 1100, where they ususally do when the engine is cold—and it will never stall again.

WTF is up with this one? I haven’t a clue. It doesn’t do it when the car is warm. Even if I let it sit for a good 5 hours after running, it won’t do this. Only after sitting overnight. Could it be the cold weather? It’s just gotten pretty chilly around here. But it isn’t any colder than it was in Ohio when I went to look at the car, and it didn’t exhibit this problem that morning when it was started.

This could be a spark problem too, I think. (It would be nice if I pull a plug and see that it’s fouled all to hell, because perhaps I could explain away all my problems with one item). It could also be the IAC valve pintle getting stuck or not extending quickly enough. In my mind, the symptoms really seem to point to the IAC first, because the engine has no trouble starting at all, it’s just that there seems to be no “floor” with the idle speed—after normal ignition, the revolutions just drop until the engine stalls. But the weird thing is, this just started happening with my new injectors. That’s what makes me nervous. It was like pulling teeth to get these injectors changed out…I’d rather not hear that something about the install was done wrong.

If I had some decent tools—a vacuum gauge, for instance, to see if vacuum is holding steady, or a fuel pressure gauge, to make sure the car’s getting good pressure at startup and that it’s not bleeding off too fast when the key is turned off—I could make a more accurate diagnosis, or at least rule some things out. But I’m operating totally blind. None of the aforementioned parts cost all that much to replace by themselves, but if you get into a “replace parts until you fix it” binge, you’re going to wind up spending a good $200-$300 on all of them combined. Not something I’d like to do right now.

I’m tempted to just break down and take it to a mechanic, give him the symptoms, and ask him to fix it. But that carries with it an $80 diagnostic charge, even if they can’t find the problem. And of course, then you’re paying for labor on top of parts. You’d pay less for the shotgun approach of just buying replacement everything and doing it yourself! And a lot of this stuff I could do myself, if I had the tools. <shatner> IF I JUST…HAD…THE TOOLS! </shatner>

Anyway, at least the car starts (although with a bit of coaxing in the morning), it runs very well once you get past the bogging rev range, and it no longer makes your clothes smell like you work at a Shell station. It’ll get you where you’re going, which is good, because KITT’s going to have to take me to work on Tuesday (and possibly Wednesday)…my Trans Am is going back to the dealer for some parts. Little story about that…you know how I’m always bitching about the dealers and how they break some part of whatever you tell them to look at? Even the radio is no exception. I had one distorted speaker, so I took it in to have it fixed. They confirmed the bad speaker and ordered a replacement. I got the car back in the meantime, and now what do I find? TWO MORE DISTORTED SPEAKERS THAT WERE JUST FINE BEFORE. It’s like somebody maxed out the 40 Hz band and jacked the volume up just to break my damn speakers! Yeah, all of this is under warranty, but Christ. Part of me really wants the damn warranty to expire so I can take the car to a real mechanic in the future.

Well, tonight when I get home, I’m going to see how KITT starts. I had to start it this morning to move it out of the way, and it did the usual stalling thing—but it seemed to take less time to fire up and actually stay running than it did over the last two days. Perhaps this problem will correct itself. Tonight, I’m going to see how it starts after sitting in the garage for 10 hours. Then, I’ll probably drive it over to True Value and pick up a cheapo Torx socket set (I have to get this damn screw out of the intake so I can go buy a replacement) and maybe a couple of specialty sockets if I find I need some to take out the spark plugs. I really want to get a look at those plugs. I have my hopes up that they will be the key to at least some of my troubles.

I’ll keep you all posted!

Categorized as Cars/Knight Project