Rough running 2000 7.4 Vortec

Hey guys I'm new to the forum. Just bought my truck yesterday knowing it had a rough idle. I've read that injectors on these engines usually don't last more than 150k and this truck just turned 170k. Truck starts and drives reasonably well. It was about 40 miles from my house and did 60-70 mph freeway driving as well as I could have hoped. The truck starts every time but it idles rough (as in making a noticeable shake) no matter how long it's been running.

Apparently you aren't supposed to adjust the timing on this engine in the way you'd do an old carbureted engine but I hooked up my test light anyway and it appears to be firing at several degrees BTDC. Hard to read the balancer right now.

I'm getting no CEL however the bulb could be burned out. Will have to hook up a scanner next chance I get. I pulled a couple spark plugs and they appeared to be ok. Cyl 1 and 3 were the easiest to get to but they looked like they'd been run a bit lean. Possible the leaky injector is further up the rail.

I'm assuming that if it were the MAF causing the problem it would be throwing a code correct? The p/o had a k&n air filter installed and it looked a little worse for wear and even quite over oiled. INtake tube was not oily. The filter did smell like gas which lead me to believe a timing issue however now I'm hoping it's not a valve issue.

I had always planned on doing Bosch 4 hole injectors on the truck I bought. Supposed to be a great improvement for throttle response and possibly mileage. I've been looking for a late 90s 7.4 vortec for several months. I know the fuel pressure regulators take a crap often too and can leak fuel Into the intake valley. You can smell raw gas under the hood when the truck starts too.

The p/o just had the truck in a shop. Found the receipt in the glove box. Truck would start and then die. Shop replaced plugs cap and rotor, fuel pump and tank sender, and the pass lock module. The truck appears to have had the thermostat pulled too. P/o says it takes a bit to warm the truck up even while pulling however after 40 miles the temp didn't get much over 100 degrees. It's possible they had an overheating issue and pulled the therm as a cheap fix.

Going to continue doing some diagnostics but any advise from guys who've been there done that is appreciated.

By the way, I know these things get horrible mileage, but I'm pretty sure I'm getting much less than 10 mpg even on the highway. I also know that the ecm will pour fuel to the engine until its warmed up and if the engine won't warm up to temp it will keep dumping the fuel to it. I know some companies sell 180 degree thermostats to sort of truck your ecm to give you more fuel and thus "more HP". I'll be changing the oil and coolant here fairly soon. When the coolants drained I'll pull the thermostat housing and see what's up.

New issue that crept up on me last night. We are building a house about 2 miles away from where we are living right now. Locally, the ambient temp has been in the 30s and 40s. Last night I got home from work (driving my commuter) loaded up a bunch of tools and drove to my lot to do some cleanup. Truck started normally as it has but barely had time to warm up by the time I got there. Some of our sub contractors were still cleaning up and asked to move my truck about 15 minutes after I'd arrived. It started normally and they moved it. About 2 hours later after the truck had time to cool down the air temp was about 38 or so with wind. I could barely get it started. Ive had the hot start issue before where you just have to crank it longer, however I have never had where you had to give it some throttle pedal to start and keep it running. Reminds me of my old '79 GMC. I had to keep my foot on it for about 20 seconds to keep the truck running. It died on me twice while starting.

Unless I'm horribly mistaken, this really sounds like leaking injectors to me. I'm going to either order or rent a fuel pressure gauge to do a leak down test but I'm going to change them out anyway. They look to be the original 3 hole style. The only other issue I've read about with similar symptoms would be the worn out distributor.

Sounds like you answered your own question!

New issue
First. I have my new injectors on order. Hopefully have them by next weekend. Gaskets, thermostat, water pump, bypass hose everything else i need is on the way. Thinking exhaust donut gaskets need to be swapped too. Hearing some exhaust

Now I'm having a cold start issue. If the truck sat for more than an hour or so it always started great. my only issue was warm engine hot start. Now I can crank on it for 10 seconds with nothing until I stick my foot to the pedal and open up the throttle body and she sputters to life. I've tried turning the key to on and letting the fuel pump prime for a few seconds, and ive tried starting it immediately after turning the key to prevent over fueling... no difference. Going to grab an IR thermometer and start checking for cold cylinders.

The only thing that has changed from when I bought it to now is that we had about a foot of snow so it has been my daily driver for about a week. No issues for the first 4 days but the last couple days have seen the development of this issue.

UPDATE:

Been a while since my last post, however I was finally able to take some time and work on the truck this weekend. Got the thermostat replaced with new coolant (the one in there was stuck open), fresh oil change, air filter and I got the Bosch injectors installed. When I pulled the upper plenum off the intake manifold it was disgusting. A couple of the runners were black confirming two slobbering injectors. Replaced the fuel pressure regulator and the small hose at the same time to fix the hot start issue. After about 10 miles of driving all appears to be great. Truck warms up just as it should, no hot start issue, no hesitation after idling at a stop light and it runs smooth. Also for the first time since I've owned the truck (since January), I'm getting water vapor out of the tail pipe, I'm assuming its a sign of proper fuel/air mixture.

One thing I did notice, the injectors I took out of the truck were a 6 hole design and not the stock 3 hole style. I will have to run the numbers stamped on them to see if they come up as a higher lb than the stock 19? I also discovered that there will probably be a new distributor coming my way in the not so distant future as well. Both of the screw holes in the distributor body for the distributor cap are cracked and the P/O fixed by using an over-sized sheet metal screw when they replaced the cap and rotor. Its tight now but I'll be keeping my eye on it.