Greetings all,

I recently installed a set of #22 Bosch III injectors from FIC in my 1992 Corvette LT1/A4. The installation seemed to go fairly well, however, I think I may have missed something.

The reason I decided to install new injectors was to correct a very high right bank BLM reading, as well as a poor quality idle (sometimes too high, sometimes too low, and always "bouncy"). Prior to installing the Bosch IIIs, my AutoXray scan tool told me my right bank BLM was pegged at 160 at idle, while my left bank was around 130 at idle. The car recently had new 02 sensors and a new fuel filter installed, and when driving the car home from the shop after this work was done, my BLM readings were still the same as before. I installed the Bosch units a couple of days later, and while the car seems to run better (noticeably more power under hard acceleration and a slightly smoother idle), it still continues to alternate between idling slightly too high (700-800 RPMs) and too low (400-450 RPMs) in around-town driving. With the new injectors, my right BLM is bang on now at 128 at idle, but now my left is at 140 at idle. My IAC counts are all over the place too, often times dropping to 0 at idle telling me the ECM is trying to compensate for false air somewhere else.

During the injector install, I wasn't sure at first, at what point the injectors were considered properly seated. The first injector I tried to install was for the #1 cylinder, on the left bank. I used liquid hand soap to liberally lubricate the o-rings prior to seating. I pushed the injector in, rocking it gently from side to side, and when it wouldn't go in any further, I continued applying pressure and rocking, thinking that it had to go in furhter. I removed it, re-lubed it, and tried again, rocking the injector from side to side and applying pressure. After several minutes of playing with this, it finally occurred to me that that was as far as the injector was supposed to go. I went ahead and finished installing all of the remaining injectors, applying more soap to the top o-rings prior to seating the fuel rails. I could feel the fuel rails "snap" into place over the injectors, and I torqued the fuel rail bolts down to the specs from my factory service manual with a good quality torque wrench.

I then primed the system by turning the ignition on and allowing the fuel pump to run and shutting it off. After priming several times, I checked for fuel leaks around the injectors. None found. I went ahead and started the car. It took a bit of cranking the first time, but eventually fired. Once again, no fuel leaks. I've put about 100 miles or so on the new inectors, and as I mentioned, the car seems to run well except for the Jekyl and Hyde idle situation.

I really think I may have a slight leak around one or more of my injector o-rings on the left bank that is causing one or more cylinders to somewhere, somehow, draw in additional air and cause the 140 BLM (lean, requesting fuel). So now my question is, is there anything that I can do without having to remove the fuel rails to detect and possibly correct the leak? And if I do need to remove the fuel rails, will it be mandatory to replace all of the o-rings at that point?

Any suggestions would be sincerely appreciated.

Regards,

Ron

Quote:

If you nicked a fuel o-ring or it was "leaking" it would not draw in air. The fuel system is pressurized and it would spray fuel out. I think the problem is unrelated.

Matthew

Hey Matt, thanks for the reply. Yeah, I guess you're right. I would most likely be seeing fuel all over my intake manifold, which I am not.

I put a fuel pressure gauge and a vacuum gauge on it for quite a while yesterday, and as much as I want to blame my strange idle issue on the fuel pressure regulator, it held 40-41 psi the whole time during idle, and 45-47 psi under acceleration. It even held the 41 psi perfectly steady after the engine was shut off, allowing pressure to drop to about 32 psi after sitting for 20 minutes. The vacuum gauge was connected inline with the FPR hose and held a steady 17" at idle when cold and about 15" at idle once it was good and warm.

I just came back from a nice long ride with the AutoXray hooked up from the very start, and I can say that I think the idle issue is definitely heat related. Outside air temp today was around 47 degrees. When started cold, idle while in park was around 725 and the ECM was calling for 850. The IAC counts were pegged wide open at 160. When the coolant temp hit 100 degrees, I set out. In drive, idle was 475 - 525 and quite rough. The ECM was calling for 675. I continued driving and as things got warmer, the idle began to smooth out bit and eventually, desired idle and actual rpms at idle were right on at 550 rpms. Coolant temp at this point was right around 195, which is where my car typically runs in stop-and-go traffic (195 - 210).

As I continued to drive however, the idle continued to creep up. It eventually got to the point where in park, it was idling at 1,100 rpm, and in gear around 650 - 700 when the ECM was still calling for 550 (in gear). By this point, the IAC counts would drop to 0 at each stop sign or stop light, obviously closing completely to compensate for the too high idle. Also, at this point, both BLMs (right and left) were right around 135 - 139. I had been doing a LOT of stop and go driving by now, even pulling over to the side of the road and letting the car idle for a minute or so, just to observe the rpms and IAC counts, and coolant temp was in the 210 - 220 range.

The car did get a new water pump installed last year in October, along with new intake gaskets and a new front seal. I'm wondering if I need to check the torque on my intake bolts. I also recently discovered that the rubber on the underside of my intake/air cleaner snorkel where it attaches to the throttle body is really tattered and torn. I have the clamp that holds it to the throttle body tightened down pretty good, but if heat were to cause that rubber to loosen up and if air were to be creeping in there, in FRONT of the throttle body blades, could that possibly be an issue?

This is all really more of an annoyance than anything. The car is VERY driveable otherwise. It's just that I'm so close to having it PERFECT, ya know?!!

A vacuum leak can definitely cause idle quality issues. Have you tried spraying some cleaner around the intake manifold while running to see if the idle smooths out? I don't remember, did you replace the IAC? How is the wiring to and from it?

Matthew

The IAC was replaced last year with a new AC Delco unit, at the same time the IAC passage was cleaned out. The wiring looks to be okay. A tiny bit brittle, but otherwise okay. I'm seeing IAC activity on the scanner, and I can feel the changes in idle as they're being made, so I think I'm good there.

I haven't tried spraying anything around the manifold because frankly, I'm a little bit afraid of doing that. With all the sensors and what not all over the place, I'm concerned that something is going to get wet that shouldn't. I'm fairly certain that I don't have any vacuum leaks in any of the typical lines running around the intake manifold, as I have examined them all for strong connections and cracks, plus my mechanic ran smoke through the engine with his smoke machine last year and told me he couldn't find any issues.

I'm really beginning to key on the intake coupler between the throttle body and the air cleaner assembly though. I know for a fact that there is likely air leaking in and/or out of that thing. It has a few tears in it on the bottom of the connection to the TB, and doesn't seem to have a very good seal at that point. I was under the impression that, theoretically, since the engine is sealed from behind the TB blades back, you could completely remove that part, and the engine would still continue to operate as normal, save for the fact that you would have no air filtration.

Is that not the case, or would a leaky intake coupler be considered a "vacuum leak"?

A leaky coupler wouldn't be a vacuum leak per se. But if you have unmetered air coming in behind your MAF or somehow behind the TB that could mess with your idle.

Matthew