backtothe80s

Hi all.

Ok, so a little background. I replaced my fuel pump and sender last June. AC Delco sender and Walbro pump. I had the tank cleaned and coated inside and out. At that time, I replaced all rubber lines, strainer and the filter.

I also replaced my Fuel Pressure regulator diaphragm and installed a South Bay adjustable regulator.

I did not replace the Bosch III injectors at that time. They were installed with double o-rings.

In chasing down a loss of fuel pressure problem (watching gauge and pinching hoses), I determined my injectors were leaking. Wish I'd replaced them when I did the FPR.

Fast forward to last month.

I ordered a set of Bosch IIIs from South bay (with spacers) and installed them.

I also smoke tested the car and found no leaks.

Since then, the loss of fuel pressure seems to have improved, but I now have several new issues I need help with.

1. Hesitation off the line and surging at low speeds. Problem is more pronounced when cold and when the A/C is on. Car seems to be down on power.

I did an injector drop test cold and found two injectors were flowing less. I ran the car and retested. Those two injectors flowed more consistently.

2. Very loud ticking coming from FPR. I can feel the regulator ticking in my hand. Did not do that prior to injector swap. I've heard the rail can be too tight and cause this.

3. When driving home yesterday, I noticed the normally kind of loud Walbro got a LOT louder. Just for grins, I opened the fuel cap and it seemed to have more pressure in it than usual. It was hot yesterday, FWIW. (about 95). While pressure testing, I accidentally dead-headed the pump at least once. Even with the increased noise, the car's performance didn't seem to degrade. Also, the noise seemed to react to voltage. It would decrease when I turned on lights and held the brake, for example. Bad ground somewhere?

I have a feeling I'm replacing a fuel pump soon and sending my injectors back to south bay for testing.

Any thoughts or suggestions? Thanks!

Fast355

iTrader: (2)

Get you a set of cleaned and flow matched LT1 injectors. Grind down the fuel rail stands on the intake so that they will seal to the intake manifold with the TPI style fuel rail injector retaining clips in place. I have run multiple TPI engines with them both MAF and MAP. NEVER run across any issues swapping them. I have had nothing but issues trying to run Bosch injectors with GM ECMs. Even the OBD2 stuff HATES them. I started tuning a LS 6.0L truck and on startup was throwing random injector codes, missing and running like crap. It had ebay Bosch 42s in it. Swapped them for used GM 8.1 Marine 42 lb/hr injectors and the truck ran beautifully on the same tune. I would run reconditioned OEM injectors before running New Chinese junk.

The OEM LT1 injectors are good to around 400 hp at the crank at stock fuel pressure and upwards of 450 hp @ 50 psi. This car is a swap from a LG4. Has a 10.5:1 355 with Dart Iron Eagle 180s, GM Hotcam, ported stock base, cleaned up stock runners, ported plenum, headers, 3" Y-pipe and a good 3" magnaflow catback. Cleaned LT1 injectors on it. Some of you TPI guys probably notice the lack of a TV cable. It has a 2,600 rpm stalled TH400 behind it with a kickdown relay activated by the 7730. Car also has a 2.42 rear gear from an ElCamino to keep the revs down on the highway. With the TPI torque curve and stall it does not need a deep gear at all. When this car had a Q-Jet it ate two well built 700r4s.

TORN

iTrader: (17)

Where is the fuel pressure set too? Those injectors are going to require a tune to make them right most likely.

southbay08

HEY MAN, GIVE US A CALL...LET'S SEE IF WE CAN FIGURE OUT IF YOUR ISSUE IS FROM THE INJECTORS. IF THERE IS ANY DOUBT WE'LL BE MORE THAN HAPPY TO PUT THEM UP ON THE BENCH FOR YOU

516-442-4707

backtothe80s

I'll call you today or tomorrow. Thanks!

backtothe80s

As I understand, the Bosch IIIs are plug and play and do not require tuning. Fuel pressure running is 44psi with the vacuum source disconnected and plugged.

backtothe80s

Fast, that's an impressive setup. I'm keeping mine stock. If I can't my injectors sorted out, I'll keep the LT1 option in mind.

That said, what clips would I need?

Will the fuel economy suffer as I'm going to 24# injectors or will the TPI ecm compensate?

How much would I typically grind off the fuel rail stands?

What's a good source for those injectors? Find a good used set and have them cleaned/tested?

Thanks

ULTM8Z

It may "run" but it's not going to run optimally. Your Injector Pulse Width vs Battery Voltage needs to match the performance parameters of the injector.

(all due respect to the injector shops on this site... but this was my experience with Bosch III's)

I struggled with all sorts of injector issues when I swapped to Bosch III's... initially to a set of modified 30 lb/hr bought from a fellow member here (who bought them from an well known injector house). BLM's were all over the place... completely inconsistent from run to run, hesitation, lousy fuel mileage, etc.. Contacted the injector house who simply threw some generic datasheet at me which did absolutely nothing.

Not until I got hold of a used set of factory Ford injectors with the factory Ford injector datasheet, from which I plugged in the voltage offset values into the calibration, did I finally get the system to run properly.

Frankly, as soon as I fired up the car with the Fords and the correct voltage offsets, I knew something was different (and for the better). It just "sounded" like it was right, and when I took out for a drive I knew immediately I solved the problem.

Any rate, it sounds like you're running into similar issues...

https://www.thirdgen.org/forums/diy-...r-offsets.html

backtothe80s

Yes. Fuel mileage has been **** poor and BLMs are always high. They are 160 at idle. I was hoping a fresh set of IIIs would solve that problem.

I will investigate and see if there are any vacuum or exhaust leaks that could be fooling the O2 sensor. That's on the list.

With this motor, I'm not interested in modifying it and I don't have the time to get into modding chips right now. Major props to the guys and gals who modify their PROMs, though! If need be, I'd purchase a custom chip.

I just want to get it to run the way it was meant to from the factory.

That said, is there a good stock replacement injector for the L98 if I have to give up on the Bosch IIIs? SMP? AC Delco? ACCEL?

Thanks, ULTMA8Z!

ULTM8Z

The thing is, each injector is going to have it's own characteristics. Some may be closer to factory L98 than others.

The best thing to do is get the accurate data data sheet and simply reprogram the chip to match the injectors

Fast355

iTrader: (2)

I usually use GM injectors because of this.

The first LT1 injector setup I used ran fairly very well on the stock chip but it was a complete mismatch to start with. Ported Vortec heads, LT4 cam w 1.6 rockers, Tri-Y headers, 2.5" dual exhaust all wrapped in a 1983 G20 Van.

Eventually I got it dialed in nicely. Used injector constants out of the LT1 PCM to get it perfect.

The ECM in the Firebird swap came from the G20 Van and the Firebird fired right up on the old chip for the Van that was still in the 7730. The setups are not all that different.

My Express van 350 with the LS 0411 PCM runs stock LS6 injectors in a L31 Marine intake. Injector calibration is straight out of the 2002 Vette tune. I replaced the stock marine injectors becase I did not have values for them from the marine MEFI ECM. It worked so well that with stock MAF and intake ducting from the 2002 Express, when I disabled the MAP blending to tune the MAF it was nearly dead on despite a cam swap.

Street Lethal

iTrader: (16)

A vacuum leak would cause a high idle and surge, and an exhaust leak would cause a surge at idle.

If the injectors are flowing in accordance to what your fueling is programmed for in the chip, then the slightest deviation in terms of injector spec is not going to cause the BLM to go that high at idle. O2 correction will make up for it, but a 160 BLM is way out there in terms of the correction spectrum. It sounds like either your charging system has a problem; check your alternator, battery and ground connections, as well as the alternator and battery themselves, either that or you need to ohm each individual injector. The biggest complaint of the Bosch III's were the differences in ohm when purchased new, as anything less than 10-ohms is bad, and many had that. I would also plug a noid light into each injector harness to see if every one of them is being pulsed...

ULTM8Z

One more reason I believe what believe...

https://www.thirdgen.org/forums/diy-prom/730802-bosch-iii-injectors-not.html

Street Lethal

iTrader: (16)

Remember that when changing the injectors, he more than likely removed and unplugged the alternator and disconnected the battery. I have seen similar issues coming from a loose connection behind the alternator because the user forgot to tighten the connection nut between the alternator and the valve cover on the back of the alternator. I would also ohm the injectors just to be sure though, as getting a bad batch when new is definitely not out of the norm...

backtothe80s

I'll definitely check that out. The injectors are being sent back to South Bay for inspection so I'll have plenty of time to check things.. I haven't ruled out exhaust and vacuum leaks affecting the BLM, so I'll continue the investigation and report back.

backtothe80s

That make's a lot of sense. Thanks for the explanation.

And it's possible that even a stock replacement such as the AC-DELCO 19244618 or Standard FJ-47 might deviate from the original L98 specs?

I would hope not as those are made for the 1989-1992 L98, but it wouldn't surprise me a bit.

ULTM8Z

It's possible. But the amount of difference is what will dictate the severity of the poor performance.

I had been running Bosch II 24lb injectors that came with my miniram for years without top much issue probably because they probably werent that much different than the factory 22 lb... and i didn't have to mess with anything except the injector flow constant. But as soon as I tried to migrate over to Bosch IIIs, basicslly all hell broke loose....

1992 Trans Am

iTrader: (2)

I recommend Accel Performance injectors specifically. Recently installed a set int o my 92 TA vert and they work great.

backtothe80s

I'll keep that in mind. Thank you 1992!

Been out of town. Should be pulling the injectors this week to return to South Bay for examination.

backtothe80s

Update. May was a very busy month. Sent the injectors back to South Bay. No problems found, but new screens and o-rings were installed. Runners and plenum were put back together very carefully. Car fired up and sounded better. Adjusted the fuel pressure to about 46 psi and it's seems to have the power it did before. My BLM at idle is still around 158. The BLM drops at higher RPMs. I purchased some PROMs from TunedPerformance. Nice guy! I haven't installed them yet, but will soon. He put in some injector voltage offsets. We'll see if that makes a difference.
I also spent some time looking for any other areas of possible air leaks. Nothing found. There is the possibility of exhaust leaks I haven't found. Will update as I make progress.