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New guy here with engine problems. All parts are stock. No modifications have been done to engine and engine management to our knowledge. With that said, here is what is going on. Truck is a 1996 GMC Sierra. Crew cab, long bed, C3500, non dually. Has 7.4 454 Vortec and 4l80e transmission. Driveline has 147,000 miles and engine has good compression. All cylinders read 120 to 140 PSI. What's going on is the engine refuses to run properly. First up is the MAF sensor. Had the engine light on the dash so I used our OBD2 scan reader on it. Got P0102 which is Mass Air Flow sensor low output. Replaced the sensor with a Bosch unit and cleared the code. Next engine start that same code came back. I checked all the wires and plugs that section of the harness goes through. It has a good run to the computer. No frays or breaks. I even reset all plugs thinking there might have been some resistance in the connectors. No dice. Code comes back every time I clear it. Any ideas? Next up is the really serious problem that prevents the engine from running properly when cold. Low fuel pressure. According to our gauge it only has 20 PSI max and leaks down as soon as the pump turns off. On the fuel system we have a new pump in tank, fresh filter, and new regulator. That was a pain to install as the top of the intake manifold had to come off. Still have the low pressure and leak down. We thought the injectors were leaky but the thing is lean at idle as we sprayed starting fluid in the intake tube and the idle evened out. When cold it doesn't want to idle at all but will even out at 650 to 750 RPM when warm. Any idea what is going on? We have no idea what type of pump is in the tank as the people who own the truck put it in before we were tasked with fixing it. Still have the stock one. We plan to pressure test it and if it can go up to at least 80 PSI we will just put it back in and see what happens. So, any ideas on what is going on? I can record videos if any of you want to see the engine and hear it running. If anyone can figure this out I would greatly appreciate it as this goes beyond my knowledge of fuel injection problems.

driving a 97 k2500 camper special, 4l80e with 454 vortec couple days ago I got in my truck after work and noticed it would stumble when hot, 100C no problem but a little bit warmer and i would have issues. always under load during acceleration. got home and idled in drive and it felt like an obvious misfire, RPM would drop to about 500. pop it in neutral or park and no misfire or stumbling, its been confusing me since in the mornings when i pull it out the garage it has no problems all the way to work (5 minutes highway and 5 minutes city) but end of the day and evening- same issue bought the truck with 268km now has 276, oil change every 5000k. did fuel pump (48psi at idle now) FPR, distributor cap and rotor, plug wires and plugs, ran seafoam through the intake and in the fuel tank. ive heard of distributor gears going south but id assume then i would have the issue when cold too. runs like a top at any temp below 100C, no engine light, plugged the scanner in anyways and no codes whatsoever. any help is appreciated, looked through forums for a couple days now but nothing exactly like what I'm experiencing. kevin,

I have an interesting overheating problem with my 1990 C3500 Silverado 7.4L. I recently bought the truck from an uncle who, I'm guessing, screwed me on the deal... We use the truck to tow our travel trailer (22ft. roughly 5000lb). Prior to our first voyage out, we drove the truck around town to make sure everything worked well. After a few trips to our main hike spot I noticed the truck would run warm, 220-240, for a short time and then spike down to 210. I assumed it was the thermostat sticking. So I replaced the thermostat with a 180 degree unit. I topped off the coolant in the reservoir and it seemed to have fixed the problem. We went on our first trip, now pulling the trailer, and at our halfway point, I got off the freeway to fill up the truck. about 20 seconds after we dropped our speed below 30 mph the truck spiked, redlining above 260. After starting it up, it quickly started to overheat again until we hit the freeway speeds and all was good. This behavior continued up until we hit our destination. Thankfully, my mechanic brother-in-law was camping with us. He thought it was the fan clutch but after looking at the radiator, I was about 2.5 gallons low on coolant. Since we were out camping, I used the rest of the gallon I had and filled the rest up with water. Brother-in-law said the water pump looked like it was running good and it might have just been under-filled when my uncle replaced the radiator. Ran ok until we slowed down off the freeway. It looked like the coolant would get hot and boiling out of the reservoir. I just kept topping off the radiator and driving home (picked up coolant 50/50 on the way back) Looked at it at home and noticed a leak above the drain valve. Tightened the valve about 1/4 turn, filled up the radiator and again the truck ran fine until our next trip. Same problems, had someone bring out a new radiator cap since it looked like the coolant was not being pulled back into the radiator. Coming back we had the same problem. I since replaced the hose from the radiator to the reservoir and "burped" the system by running the truck and squeezing the upper radiator hose until the coolant level would no longer drop in the radiator. The oil looks really clean (not milky or showing signs of water/bubbles). Coolant looks clean and I have topped of the radiator last with concentrate coolant to account for the water I added before. So I don't think it's the head gasket. I rotated the fan with the truck off and it stopped immediately after letting go. There wasn't any play when I tried moving the fan around so I don't think it's the fan/fan clutch. I hear an electric fan on when it's overheating/hot and the fan clutch kick in when its really hot. Rather than purchasing a bunch of new parts I thought I would get on here and ask a couple questions and see if anyone might have some things to try out. Would having enough air in the cooling system keep the coolant from being sucked back into the radiator? Could the fan clutch not be engaging at a low enough temperature? If the radiator is a 2 core, would that cause the coolant to boil enough to cause an air gap that would then keep coolant from being pulled back into the radiator? This truck was originally purchased new by my grandpa in 1991. He was a mechanic and took amazing care of the thing (all receipts). My Uncle purchased it from him a couple years back and I believe it was just sitting on his property for most of the time.

Recently (9 and 10th Oct.) had a drive with my friend (2008 Ford E-350 with 6.0 diesel) in Eastern Sierra area, used route CA-88(Stockton - Alpine Village), 89(Alpine Village - Topaz Lake), 168(Bishop - Sabrina Lake), 120(Mono Lake - Manteca), US-395(Topaz Lake - Bishop), Virginia Lakes Rd. The highest altitude was 9900+ ft at Virginia Lakes, and had a one-night camping at North Lake at 9300+ ft. The performance is expected, it performs like a mid or early 90s Toyota Corolla with 4 adults on board. At the climbing on US-395N, north of Bishop, (37°28'56.9"N 118°34'52.5"W or 37.482478, -118.581256 ), it can barely maintain 70mph, with the stupid and annoying transmission jump between 3rd and 4th gear. I believe it can actually maintain 70mph without problem if the transmission doesn't mess it up. I am planning to convert it into switch-flip manual or use stand-alone controller. And the climbing on CA-168 is really a struggle, barely 40mph, with the stupid and annoying transmission again, jumping between 2nd and 3rd gear, until I have it enough, simply put the shifter at 2, let it revs at 3500 rpm, while 4000 is the red line. So is it performs normal? Any advice on high altitude driving and tuning? Like base ignition timing? The first day, the climbing on CA-88, 89, 168 and Virginia Lakes Rd, my new air filter is higher than original slight a little bit, caused the air cleaner lid can't seal, let hot air in engine bay get sucked in, I guess it's probably make the high altitude air density problem worse. The next day, I made a gasket with shop towels to seal the lid. I feel it performs better, but since I was grouped with my friend, I can't do the test on the same route to see if it really make difference. ========== My vehicle: 1994 Chevy Suburban K2500 Silverado, 454TBI (L19)+4L80E, with towing package, 178k miles. Purchased used at 150k miles. Engine was rebuilted at 75K miles, which is the only known thing, assuming other things are stock, transmission and torque converter are factory original and weresn't rebuilted. New air filter, Engine oil changed at 175k (Mobil full synthetic), transmission oil changed at 150k. Coolant / water is 60%/40%, new radiator cap, no boil happened. (Prestone for GM, orange color) New spark plugs & wire, ignition coil, ignition control module, fuel filter, fuel pump, thermostat at 150k (right after I purchased it). //edit: O2 and MAP sensor are also new, ACDelco. Base ignition timing is 8 BTDC, factory is 4. Load: 1 person (me), camping gears, road emergency kit and 2 boxes of tools for emergency, no trailer. Fuel: Chevron or Shell 91.

Can a 454 W engine code bloc be used to replace a N code bloc? I have a seized up 454 N TBI engine and a good running 454 W 4bbl. I just want to swap blocs and keep the TBI running. It's in an early 90's motorhome and it's just to keep it running around THanks all

1994 Chevy Suburban K2500 454TBI Mileage=155,000 Factory setting: 4BTC Everything is stock. Searched on internet, looks like some people set it at 8BTC or even 12BTC to get more torque and better MPG. But seems like different year have different program, same setting on some year it runs good, some not. I only use #91 gas from Shell or Chevron. #91 gas allow more BTC, right? Anyone have recommend about BTC setting? Most time running light, only me in it with some tools weight no more than 100lbs. On a test run from San Jose (CA) via I680N, I580N, CA120E, CA99S, CA140E, to Mariposa(CA), cruse at speed limit, most 65MPH, CA140 is 55MPH, most flat, get 13MPG in average. Plan to tow an utility trailer with a fully loaded truck camper on it (I live in the camper).