Fuel Injector Upgrades

[AleroB888]

Originally Posted by MacsAre1

I just had my stock injectors tested and cleaned on a flow bench. The flow rates went from 21-22.1 lb/hr before cleaning to 21.6-22.5 lb/hr after cleaning. How come that's higher than the 19 lb/hr you mentioned?

My '99 fuel pressure regulator runs about 10 psi lower than in my '03, which would lower the flow rate, but I don't know at which pressure each was rated for. You might find out at what pressure yours were tested.

[AleroB888]

Originally Posted by AleroB888

........But soon, as the car warmed up and the computer settled in, an off-idle stumble developed. Not just from a standing start, but also a hesitation when stabbing the throttle from a low rpm cruise. This was accompanied by a little black smoke out of the tailpipe each time, and random misfires but no codes thrown. Eventually the computer's compensating made matters even worse. I tried every possible tuning combination to get a usable result, but none worked.
........................

I had this problem with the 36 and 35 lb. injectors, but not the 28's. After a test drive earlier today, it appears the problem is solved.

I demodded the car except for CAI, exhaust system, and ignition. I installed the 36 lb injectors again, reset the injector flow rate (IFR) close enough for a run and scan, let it warm up, and drove about 8 miles. This time the idle was normal, no misfires, no hesitation, good throttle response. Unfortunately, since the tranny is shot, I could only test WOT in first gear.

Looks like the problem was that the (stock-type) throttle body that I modified is not exactly like the stock one in the idle air control (IAC) opening, and needs a section cut out of the mounting flange to work correctly.

If no other problems crop up, I'll retry the RC Engineering 35's.

[AleroB888]

The GM 36 lb injectors had been in the car for about 2 months now with fair to good drivability, so I installed the 35 lb RC injectors:



I must mention here that there has been a problem with misfires on cylinder #1 since the last time I raced back in November, pretty severe when the engine is cold, and confined to low rpm. So far, it disappears at WOT. But there is definitely a mechanical problem with cylinder 1.

Base fuel pressure used is about 44, with a 2001 year model PCM program file. I had the IFR set to 33 for the GMs, and installed the RCs without resetting it. Between that and uneven flow at start up, the first run at idle was pretty shaky, fuel trims went way too far negative. After resetting the IFR twice, I wound up leaving it at 35 lb/hr, the manufacturer's rating. With ambient temps in the low 80s today, Long Term Fuel Trims (LTFT) scanned between (+5) and (-5), close to zero average.

So this means that the RC 35's have a higher flow than the GM 36's for the same psi. The Injector Duty Cycle is 8-10 percent less than the GMs at WOT.

There appears to be more random misfires with the RC 35 compared to GM 36 lb, until the engine warms up. The 28 lb Envoy/ 'Blazer injectors did much better in that respect. After only one day of use, my impression is these RC injectors will be usable as far as drivablity, but time will tell. I would really like to have them in for the next trip to the track, as they are closely flow matched, and it would be interesting to see how the single-hole design does under boost.

[MMGT1]

I've had great results using the 36lb ones. My idle is within 1% and can hit commanded AFR at WOT dead on all the way to 6600 RPM on a bone-stock pump. If youre still boostin' though, I would go to 40lbs to keep the duty cycle down. Just a thought man

[AleroB888]

Originally Posted by MMGT1

I've had great results using the 36lb ones. My idle is within 1% and can hit commanded AFR at WOT dead on all the way to 6600 RPM on a bone-stock pump. If youre still boostin' though, I would go to 40lbs to keep the duty cycle down. Just a thought man

I think the RC 35s will do good enough as far as duty cycle, I'm only up to 80 % @ WOT with 85 degree ambient temp. That compares to about 90 % with the GM 36s. I expect those percentages to go up to 85 and 95 % respectively when the weather cools back down, bypass the air filter, etc.... I think the GMs would do just fine, but I won't have too many chances at the track, so I'll try the RCs first. As it is, I'll wait for cooler days, and try to take one last shot at running a 12 second pass.

[MMGT1]

Off topic a bit here B, but have you ever replaced your crank sensor and lead that goes from the IGM down to it?

[AleroB888]

Originally Posted by MMGT1

Off topic a bit here B, but have you ever replaced your crank sensor and lead that goes from the IGM down to it?

No, it's the original sensor and lead. If about the misfires on #1, I did swap out the coils, plugs and plug wires.

[MMGT1]

They are notoriously foul bud. I was having some issues that would not show up in any scan and finally said f-it and replaced them. When I pulled the crank sensor I could physically see that the sensor was slightly "swollen" inside the block. At the dealership we replace a lot of them on the 3400's as the exposure to heat in there really messes them up bad. Even if your not throwing codes, with the stress I know your car has endured, for a 25 dollar part I would replace that one when you can man. Other than the dam MAF it is the sensor that will cause all kinds of crap before they get bad enough to throw a code.

[AleroB888]

Originally Posted by MMGT1

They are notoriously foul bud. I was having some issues that would not show up in any scan and finally said f-it and replaced them. When I pulled the crank sensor I could physically see that the sensor was slightly "swollen" inside the block. At the dealership we replace a lot of them on the 3400's as the exposure to heat in there really messes them up bad. Even if your not throwing codes, with the stress I know your car has endured, for a 25 dollar part I would replace that one when you can man. Other than the dam MAF it is the sensor that will cause all kinds of crap before they get bad enough to throw a code.

Thanks, I'll do that. Any other advice on how to replace it is appreciated, which brand, etc.

[MMGT1]

Kinda tricky to get out but not too bad. Use brake clean and spray the crap out of the area where it mounts to the block. then spray it with lube before you pry it out. Do your best to lift it straight out as this one can break! Get one from GM bud. Like I said it's about 25-30 bucks for one State side I believe. Use electric grease on the seal of the new one before you install it.
The connector between the module and the sensor is a little costly up here, around 100 bucks, but I would replace that at the same time. It runs really close to the coolant lines back there and causes a lot of damage to the sheeting around the wires. They will actually fuse together from the heat. Pretty straight forward to do. Because of the headers I had to go through the wheel well to get access to it. Made a huge difference to my idle trims and how the car ran after being on the highway for any length of time.

[AleroB888]

Originally Posted by AleroB888

The GM 36 lb injectors had been in the car for about 2 months now with fair to good drivability, so I installed the 35 lb RC injectors:

................I must mention here that there has been a problem with misfires on cylinder #1 since the last time I raced back in November, pretty severe when the engine is cold, and confined to low rpm. So far, it disappears at WOT. But there is definitely a mechanical problem with cylinder 1.

Base fuel pressure used is about 44, with a 2001 year model PCM program file. I had the IFR set to 33 for the GMs, and installed the RCs without resetting it. Between that and uneven flow at start up, the first run at idle was pretty shaky, fuel trims went way too far negative. After resetting the IFR twice, I wound up leaving it at 35 lb/hr, the manufacturer's rating. With ambient temps in the low 80s today, Long Term Fuel Trims (LTFT) scanned between (+5) and (-5), close to zero average.

So this means that the RC 35's have a higher flow than the GM 36's for the same psi. The Injector Duty Cycle is 8-10 percent less than the GMs at WOT.

There appears to be more random misfires with the RC 35 compared to GM 36 lb, until the engine warms up. The 28 lb Envoy/ 'Blazer injectors did much better in that respect. After only one day of use, my impression is these RC injectors will be usable as far as drivablity, but time will tell. I would really like to have them in for the next trip to the track, as they are closely flow matched, and it would be interesting to see how the single-hole design does under boost.

After a few days of testing, I found the drivability of the RC Engineering injectors not acceptable, so the GM 36s were reinstalled. Nothing other than Injector Flow Rate (IFR) was recalibrated for these tests, and it's still possible that the RCs can be made to work. But since the GMs are less problematic, I'll keep them in for now.

I settled on an IFR of 31 and did some scans yesterday, with (much lower than normal) ambient temperature in the 60s. Just a few days before, the temps hit 100 degrees. Setup was in street trim, 1/4 tank of gas. On the first scan, the Injector Duty Cycle (IDC) hit a maximum of 94%, with decent Long Term Fuel Trims, (+2,-7 %) and no Knock Retard (KR). That was much better than I'd seen in the last few months, and don't expect it to be typical, but seems to be moving in the right direction.



IAT (intake manifold) at start of run = 75 degrees, end of run = 93 degrees. Boost peaked at 11 psi