Hello everyone,

This is our first post to this forum, and we need help. First, we bought a Z28 ('94) with an engine problem, then a second one with a MONSTER engine to swap. Now we have trouble. There are lots of long boring details in the middle, but opted to leave those out for now. Anyway, here's the breakdown : LT1 5.7L, BBK headers, MSD6AL, Stage 2 ported and polished heads by Craig Caulk Racing Heads, 2.0 INT valve 1.6 EX, 52mm throttle body ported and polished, port and polish MAF, 290/307 Comp Cam .510 INT .540 EX, 112 lobe seperation, 1.6 Comp Mag rockers, Holley 510-502 AFPR, TB bypass, Hypertech air foil, Magnaflow 3" catback exhaust, soon to be installed, rebuilt (killed it) 4l60e with kit from Probuilt Automatics w/ Edge Racing 3000 stall, 3:42 gears, cold air induction, 26 lb Venom injectors, MSD 8.5 mm wires, Custom tuned PCM by PCM for Less. Was told by the fellow that built the car all this good stuff came out of was supposed to be around 500fwhp. Here's the problem: It had 24 lb stock injectors without MSD 6AL when we got it, and was loading at idle. Installed the MSD and 26# injectors, ran great for about 30 seconds. Then the dreaded black smoke from exhaust and strong fuel smell. Car died, put fuel pressure gauge on it, 40# immediately, once injectors stopped pulsing, fell to 35# then straight to 0 like a rocket. Do I need a Walboro 255, and stay with the 26# injectors? I have no clue how this car ran like crazy with time slips to prove 12.80s with slipping tranny with previous owner. Can you get that on the stock injectors with a stock pump? The guy that put all the goodies in said he was unsure if pump was upgraded. We are the 4th owners of the car. Owner #2 put all the goodies on the car. Owner #3 lost all the receipts, records, etc, and had NO CLUE what was going on. This is our first toy with fuel injection, but have lots of experience with carb toys. Thanks for any advice/help.

 

A stock fuel pump will support 26# injectors, but 26# injectors aren't going to support a 500fwHP engine, at least not at stock fuel pressure. You will need a new fuel pump and injectors closer to 35#/HR.

Not clear from the above.... did you use the PCM that came with the "monster" engine? Is that the one that has a pcmforless tune? How did the engine make 500HP with 24# injectors? It isn't possible, unless they were running 55-60psi on the fuel system.

And, if the PCM was correctly tuned for the 24# injectors that were in the engine, it shouldn't have been pouring out black smoke. And throwing in 26# injectors on a 24# tune will only make it run richer, although not by much.

The numbers don't make any sense.

To test fuel pressure, try and get the engine to idle. Pull the vacuum compensation lone off the fuel pressure regulator and see what the pressure is. Put the vacuum line back on, and the pressure should drop proportional to intake manifold vacuum..... may only be a 5psi or so drop with that cam.

 

Thank you so much for your reply. A little more detail on the problem with the car. Before we swapped the engines, the donor car was running very rich, don't know what the fuel pressure was, I figure probably jacked up somewhere around the 55 to 60 psi, and it does have the adjustable regulator. Ran rich again after the swap to our car, and we installed the MSD6al. It ran very strong, but rich at that point and was loading at idle. Car began loading even more, so we changed the injectors thinking.... these are stock, and old, possibly leaking. We happened to have the 26# new injectors and installed them to see if things would improve. It ran great for about a minute, and it was then that it started sputtering, smoking black, and died. Checked fuel pressure, and found the results I mentioned in my last post. The PCMs were swapped out as well, so the custom programmed one went with the engine to our car. I was wondering how on earth those numbers and hp could be achieved with the stock injectors and pump (BUT we are not sure that this is a stock pump in the donor car). The previous owners have no idea, and the original owner that started the whole upgrade can't be located. We have been working blind for the most part, as far as what was done. We have been able to piece together what was listed above on the mods in the last post. I also figure with the new injectors, pump, and prob 160 degree term (while we are at it), the pcm will have to go back to be redone. Sometimes I wonder, what have I gotten into??? LOL Any info you can provide is appreciated!

 

Have you checked with pcmforless to see if they have a record of the "tune"?

Have you scanned the PCM for codes?

What is the model year of the engine and PCM you are currently running? Is it an OBD-I or OBD-II setup?

Running excessively rich can be caused by a "false" lean. Is your exhaust system buttoned up tight, eliminating the possibility of exhaust leaks before the O2 sensors? Are the O2 sensors located to as not to be exposed to air backwash, if you are running open headers?

What brand O2 sensors are you using? False lean could also be caused by faulty O2 sensors. Most people here have found that the Bosch O2 sensors do not provide reliable performance, and replace them with the OEM AC/Delco sensors.

Pull the vacuum line of the AFPR and see if it is soaked with fuel, indicating a failed diaphragm in the fuel pressure regulator.

 

We are waiting on Bryan at Pcmforless to email me back with all the info on the programing. No i have not had a chance to put the code reader on the car. the enging and pcm both are from the 1994 donor car. Both the donor car and our car are 1994. I will try to check the vaccum line on the afpr this afternoon and send you a reply of the results.Thank you for all of your help thus far. As we mentioned we have been in the dark for a while.

update: Learned that the PCM was tuned for the 24# injectors. Not running open headers. Also was able to scan for Codes this eve. Here's the result: (1st try) Not able to crank the car, but it did turn over, codes 36 High Res Pulse Circuit, 42 Ignition Control Ground Circuit, 48 MAF Circuit, 51 PCM PROM Flash Error. Cleared the codes. (2nd try) Got it to crank, car backfired, sputtered, would not idle, and couldn't keep it running under half throttle, would not turn high rpm, black fuel smoke everywhere. Scanned for codes, 36 popped up again, but no others. Cleared codes, (3rd try) Car ran the same, code 36 was there again, but nothing else. Are we talking Optispark prob here? In addition to the need for bigger injectors and fuel pump? BTW, the pump is coming on at least. unable to do fuel pressure check, the gauge seems to have walked away from the house somehow......