Fuel pressure ok?

If you have a steady 40 psi fuel pressure reading, then I would say that you don't have a plugged filter or a fuel pressure issue. Whose ECU are you using to run your injection system? Back firing could indicate an ignition problem. You need to get into the program and check the fuel air ratio settings along with your ignition settings. I am running a FAST XFI 2.05 system that is port injection and in sequential mode and my normal fuel pressure is about 39 psi. I also have a 9.2 deck Fontana block, but am using CHI 3V heads and displacing 388 cubic inches.

39 psi should be fine.  Jffr, are you running eight stacks? If so, are you using a remote IAC valve? Are you running the FAST or the Holley dual sync distributor? I'm running the FAST XFI 2.05 with individual throttle bodies without the IAC valve and need to adjust the cold idle rpm tune. I also have a Fontana 9.2'' deck hight displacing 422 c.i. running in bank to bank mode right now, will be switching to sequential mode eventually with the Holly low profile dual sync distributor which I already have. Any input would be appreciated! Thanks

I have the MSD 6AL ignition system.  12 years since I owned the car and its the first time it got a bit funky (besides the time I had to change the two filters and in Dec when I cleaned the plugs). Now I'm thinking maybe it wasn't the plugs needing cleaning but instead something else. Not sure what's up with it, way beyond my scope of abilities if its something up with the ECU/ignition system. Will probably just need to drive it in to my fuel injection engine guy. He programed it when I first got the car. Maybe they occasionally need readjustment? Its not real bad but I notice its not up to par like it usually is. I thought maybe it was a warm up issue, but I ran it a good while and didn't improve.

Jan, is it possible you just got a contaminated batch of fuel? Before you start digging around, maybe degas the thing and refill with some fresh, known-good high octane.

Good thought bossman. I was actually thinking the same, I have one 5 gal can to take out the existing gas but just need to grab another 5 gal can to put in new. I'd like to take out as much as possible and I think I have about 5 in the car now and could run it in the driveway a bit to squeeze out some more or use other containers. I really thought it was the gas filters acting up again, but that 40 psi looks right. I always use the same place for all my cars but who knows bad gas may be a longshot but worth checking anyway.

Well I syphoned out the existing gas from the car (after tasting some) and put in 5 gal of new gas. But in doing so I noticed the gas from the car (Mobile 91 octane) looked quite a bit darker than the new gas (Chevron 91 octane). I only assume a different brand gas could have different color, but who knows I'm no gas man (the wife could debate that!). Anyway in the photo Mobile is on the left and Chevron on the right. Didn't take the car out yet though. If the car still runs odd I may try and rig my gopro near the fuel pressure gauge in the engine bay to see what the PSI is under load.

Jan, as gas ages it starts to tarnish like that, it has lost some of the volatiles.

An ECU map shouldn't need updating, what is likely occurring is one of the inputs is reacting differently, a sensor or maybe an injector clogged, especially is the vehicle is sitting for long periods. What are you running for a MAP/MAF sensor?

Yeah it seems something is a bit off. One time it even stalled just after start up and idling.  I usually get it out for a good run at least every couple of weeks, but back in January had to let it sit for close to a month. I wonder if I just run it more or just start it up more if it may work itself out on its own such as if gums & varnish happened from sitting. Anyway, will test it out next week with the new Chevron gas in it. I am not sure of the specs on MAP/MAF but looking at build photos it seems it has a Speed Pro ECU (that is if it didn't get changed out from when I bought it.

Still a bit rough with the new gas, so I put in some Techron fuel system cleaner anyway and over time see if that has any improvement. Not sure what's up with it. Trying to locate the pressure regulator next. I see some references that say the fuel pressure gauge should maintain pressure when you turn the car off however mine shoots right from 40 to 0. But maybe that's normal for my car with the set up I have. Talked with the fuel injection manufacture and he suspects the throttle body. It seems there's 4 with my car but probably beyond my capabilities to get into that. In the end may need to just drive it to Harv in Whittier.

The fuel pressure drops off after a few minutes or less after you shut your engine off. You really should get you car hooked up to a lap top and see what is going on. Have you tried checking your exhaust header tube temperatures with an infrared temperature gun? That can at least tell you if you are getting good and even combustion on all cylinders.

Thanks for the gun suggestion. Funny I was just thinking of that too, since I am unsure of the real problem. Will need to buy one, any suggestion for heat range? Amazon seems to have several weeks back order on all of theirs, but a parts store here has one that goes up to 840 degrees. I also have a code reader as well that I use on my other cars on occasion, so I may look to see if I can find the input (if there is one). Never saw one under the dash, but could be near the ECU.

Get a thermal gun that goes to 1500 degrees "F". That should be all that you need to check header tube temperatures. I doubt that a modern day automotive code reader will work on your after market ECU. As far as I know all of the after market companies have their own program and you need their software program to get into the ECU.

Thanks. In the link below is about all I could find, reads to 1112. Maybe it will be good enough if I don't get the car too hot.

Amazon

 I tried this for analyzing fuel mixture. Don't be surprised by considerable variation in temp. from these guns. I found the average idle temp on header pipes not far from the heads was around 980F on a Costco temp gun. Shooting the exact same spot on multiple round tubes is difficult, and minute changes in vertical distance away, angle or position can change the indicated temp by 100F or more. You can't tell if its exhaust gas temp variation, or whether its because the spot you checked is not identical on all 8 tubes. Or if its just a cheap gun.

The lower the temp, the less all this seems to affect the gun reading. So its much more accurate on radiator header tanks and useless for checking exhaust mixtures. My 2¢....

Thanks all. I still may get that heat gun, as I probably should have one anyway. Willing to give it a shot just to see if there is any drastic temp differences. I may even take off a stack to take a look at how the throttle body looks inside. If its easy to do, I suppose I could look into each throttle body because the manufacturer said sometimes those valves can bend with a backfire. It looks like I just unscrew these couple of screws on each side and the stack should come off.

A 1200 degree max temperature gun will work. You are just looking for major differences in exhaust temperature.

I have been bothered from the first post , but  rather reluctant to chime in.

The fuel pressure caught my eye.  In a FACTORY EFI system with a fuel pressure regulator and return line to the fuel tank , the pressure varies.   At idle and low loads the fuel pressure would be more like 28 psi and as engine load increases the pressure also rises by about 8 to  10 psi.  That is done so the pressure across the injector remains constant. (delta is the term)   The fuel pressure rises to match the increasing manifold absolute pressure.  (decreasing vacuum)

The picture you posted shows a fuel pressure regulator with a small hose on the right side of the regulator. (passenger side)  That should be your reference to the manifold pressure.  To test it , you would pull the hose off with the engine running and fuel pressure would go up that 8-10 psi.  The hose should be dry , any fuel and you have a regulator problem.  There should also be some vacuum at the now removed hose.

  I have zero experience with a engine with IR manifold and efi.  I understand the "vacuum " signal can be erratic.  (bounce around)  Most manifolds have all cylinders drawing from a common plenum and one large throttle body to meter air flow.  Manifold pressure (vacuum) is more stable .

   I would look to see the small hose is connected to the manifold and in good condition (not rotten).  It is possible the MAP sensor has lost it's connection as well if not bolted to the manifold directly.

   I use the Harbor Freight contactless infrared thermometer for $25 .  I use it for "looking" for heat in brake rotors and bearings.   A industrial quality instrument has a correction factor that has to be entered for the material you are scanning. Copper vs steel vs skin vs what ever.

   Another thought is a scan tool does NOT pick up all faults, only sensors that are monitored.  It can not tell a clogged air filter or tell a bad plug wire from a fouled plug.  They only point you in a direction.

   Boss wrench has good advice , start with the logical and simple things and work your way throgh the problem rather than go full "Mike the Snake" mode.

   I hope that is food for thought and wish you luck in your repair.

   Please keep us posted.

The only eight stack EFI system that I worked on had a vacuum chamber that was being fed by lines that came off of each throttle body. It allowed for a constant and stable vacuum reading. I agree that the photo of the fuel pressure regulator does seem to have a small line on the right side which looks more like a vacuum sensing line than a fuel return line. The aftermarket fuel injection system that I am using in my Pantera is a FAST XFI 2.05 and it has a rather large fuel return line that comes off of the pressure regulator and goes back to the gas tank. The fuel pump pressure stays the same at all  times. I have watched it from the ECU on the dash monitor and my in dash fuel pressure gauge. There is also a mechanical fuel pressure gauge that is on my fuel pressure regulator. It sounds like over kill on my system, but I already had an in dash fuel pressure gauge in my car before I switched it over to fuel injection, so I just replaced the gauge with one that worked with the higher fuel pressure that EFI has. Many newer factory EFI systems use a variable pressure fuel pump which does change fuel pressure according to load. I also agree with just starting to look at simple things on this system, but the best approach is to start with getting any fault codes that are coming up in the ECU. That of course means hooking it up to a laptop with the correct software program. This entire problem could still just be a batch of old gas that needs to purged out of the system. The simplest way to do that is just get the car out and drive it like you stole it until it clears itself out!

Yeah thanks for putting up with my dumbness. I could just take the car in, but I like to learn as well. If my engine guy was more local I could just drive it in and may do so in the end. Yes I have been trying to find the fuel pressure regulator, so maybe this is it as shown in the photo (the piece top of the gauge?). I did inspect that small tube on the right and that hose is connected at each end. Maybe that's the vacuum hose? I didn't go pulling on it because I thought maybe it was heat wrap secured and didn't initially want go pulling on it. I do have a vacuum test tool, so if that is the vacuum hose I could try pulling it off and testing. I still think its a bit odd though that my PSI drops so fast when turning the car off, because from google searches it seems to indicate that PSI should remain at least for a few minutes. I forgot all about Harbor Freight for tools, so I'm on my way to pick up the heat gun because I figure its good to have one anyway.