Hello, after reading a lot here i decided to join and ask my question with hope that some of you grearheads may have an answer. I drive a 1992 p30 chassis motorhome with a 7.4L 454 tbi in it. A while back I had a backfire and then loss of power. I brought the RV back to my friends' shop and if I remember correct we replaced the ignition module the ECM had fried and that was that. The car then seemed to run good until I went up a hill.
Long story short I rebuilt the motor with a new timing chain, lifters, (didn't touch the cam, it showed no wear), machined heads and new exhaust manifolds. I had the catalytic converter out and the muffler they are fine. There was no restriction. New spark plugs, rotor, cap, actually a new distributor, coil, map sensor, EGR was fine, new coolant sensor and oxygen sensor, started it up and it fired right up. We played with the timing at 4 degrees TDC, 8 and now it's at 12 and it is back to the way it was running. Good power in the city. Engine does not overheat it purrs. Now, when I go up a hill I still have the same issue! Both sides of the exhaust manifolds glow and if I give it more gas they just glow more. I noticed when I give the car a good amount of gas on a straight road for let's say 10 seconds, it's no problem and before you know it I am at 75 mph. If I do the same amount of gas going up hill, after ten seconds they glow.
I hooked up the shop's snapon computer again today and it didn't show any codes. I replaced the knock sensor also. When the car goes up a hill it does not overheat. Temperature is steady at 200 degrees and the clutch motor fan comes on as it should. Oh, I also put in a new thermostat. I replaced the fuel pump also because I had an extra one and I put a fuel pressure gauge in line. It reads steady at 10.5 psi (9-13 is spec.) By the way the MAP sensor tested out good so did the ignition coil.
I made friends with the shop foreman at the local GM dealership and he put his scanner on it and he says at idle it runs a little rich but not alarmingly much. I checked the engine ground and it's good. So is the battery ground. I rebuilt the fuel pressure regulator also. There are no leaks and all the vacuum lines have been replaced. The intake manifold has a steady vacuum reading. Everything was torqued to spec and the car runs great, idles great, and sounds like a killer chevy. Lastly, I took the injectors to a shop here and had them flow tested. This shop does it with the injectors sitting in the throttle body so I had to bring the whole thing to them. The test outcome was that they are both good and they both flow 510cc. Now I found an online calculator and that turns into almost 50pph. The part number on the injectors reads GM17084304RPD. Now, my online studies point toward the fact that they indeed are the correct part number for this vehicle (p30) but that these injectors should flow 75/80pph. Some say the fuel pump should be at a solid 13 and not between 9 & 13. So this is now overwhelmingly confusing. I learned a lot on this journey and it's now at a point where everyone I have asked about this is out of ideas.
The computer that is in it is a replacement one and it has no part number on it. it just shows this: NUMBER: 7-7060 and DC CODE: 1212GD The old prom was used and it says this on it: AWUJ. The gentleman at tbichips.com says that he can reprogram my prom and all of this stuff will go away but I am holding off on that because the vehicle wasn't doing this and I shouldn't have to modify things in order to get it back on track. I know I can do a lot of work and programming to make it better but I feel it shouldn't have to come to that. So there it is. I'd love to hear some suggestions from you folks. Thank you in advance for your time and knowledge.