Hi everyone. I have a 98 with a 4.3 vortec I bought to resell. I thought it had a bad engine when I bought it, rod knock or something. Well, long of the short, I found out the flywheel was broken. Like broken in two. Of course I had the engine and trans out by that point. Put the engine and trans back in with new flywheel, motor mounts, and a few other small things.
I hook the battery up to try and start it last night and the fuel pump immediately come on and ran the whole time the battery is hooked up. Even with the relay pulled the fuel pump runs. The truck would crank over but wouldnt run, just sputter and backfire. So I thought the engine was out of time, so I pull it apart to check the timiong chain. The engine was still in proper time, so I set the distributor by the cam/crank timing marks and put it back together. Now this miserable thing wont crank over and the fuel pump still runs nonstop.
One thing to note is when I put the truck back together I accidently had the ecm upside down in its little bracket. I dont think this would affect it, but I normally work on musclecars with a carb and points.
I have it on a lift so I can get underneath it easily and I have not found any damaged wires to cause this mess. I just want this silly thing to run and drive. I am at a loss as to what coul be wrong and I am seriously considering sending it to the auto wiring shop.
Anyone else had a similar issue?
Thanks in advance, Kramer

 

Get the correct wiring diagram. Without it is like trying to get someplace without a map. Get a multimeter and learn how to use it. When you troubleshoot the fuel pump issue, I bet you will find the other problem. (No start). Good luck!

 

well the fuel pump constantly running with the battery connected is very odd especially with your relay out, no insult at all meant by this but are you sure its the right relay u pulled out? my thought is your fuel pump test wire located over on the driver side to test the pump is possibly connected to a power source maybe by the previous owner that would cause the pump to run constantly with the battery connected for sure check into that and let us know

 

I have a wiring diagram from a 97 blazer and a 99 blazer. I dont have the 98. The 97 has 3 sources of power that could supply the fuel pump. The 99 only has 2. If your 98 is similar to the 97 wiring, then you could have a failed Fuel pump switch/engine oil pressure sender. Very important that you verify the year of your vehicle. DONT look at the tilte though. Look at the manufature date on the door pillar. Good luck!

 

Ok I got some of this stuff fixed. I unplugged and reinstalled all the connections on the engine and the fuel pump began working normally, so, knowing the timing chain was right, i stabbed the distributor again on number one with the left timing mark lined up with the timing cover. and it started right up. I was not getting a signal from the crank trigger so that was replaced. I have checked and rechecked for shorted wires. Now it is difficult to start especially when cold, and it shifts when it wants to and sometimes wont shift ata all. I have access to a big fancy computer scanner. the scanner reads 2nd gear in every shifter position except low. in low gear it reads low on the scanner. the guy with the scanner says it has to be in park or neutral to flash the ecm for the new crank trigger, which is the only code it shows. after finding no shorted wires, I thought it was the ecm, so I got one from the junkyard from a 99. mine was mfd 9-98, so it barely made the 98 model year. Well i installed the junkyard ecm, and no start. I put my old prom chip in the junkyard ecm and no start. So I reinstalled the original prom/ecm and it finally started. still same issues with hard to start and sticking in second gear. Does the junkyard ecm need to be reprogrammed to work in this truck? Original prom or junkyard prom? The numbers differ on both the ecm and prom from my original parts. Any ideas? All I lack now is getting the new crank trigger to work with the computer and that stupid shifting issue. I want to sell this heap and get on with my life. If I did not have Like 800 dollars tied up in this thing Id just crush it.
Oh, the no start issue was the cable popped off the trans. It dont start in reverse too well.
Thanks in advance for the help. i hate this truck

 

I may have the solution for partial problems, Here's what I ran into and the fix.

All issues were intermittent, The vehicle would turn over but not start or mild sputter then die(from residual fuel in line when switch would work), majority of the time no start. No power to fuel pump or key on power at relay.

I was unable to shift when the key was engaged in the start or run position.

The battery would die(drain) every 3-7 days.

NO dash light(start up dummy lights) at key ignition or run position.

Radio would work or not work.

Alarm would not register that vehicle was in run position.

It was the Ignition switch module, I would investigate it further if any of these sound familiar, it is the black box located underneath your key right side inside the steering Colum, there is only two torx screws to access it.

Good Luck

 

Oh, the oil pressure sensor was junk too, but the fuel pump started acting normally before I changed it. I still have no idea whats wrong with it. I still think ecm

 

I just want to verify...When you bought it you believed there was a rod knock which turned out to be a bad flywheel. Were there any other issues with the truck or did this all occur after you bought it? So many times I have created my own problems while doing a motor R/R. Concerning the crank sensor code: Has it cleared? if not, did you probe the computer connector to verify continuity or did you do a hand over hand? I would probably hold off condeming the ECU, Remember basic computer classes? "Garbage in = Garbage out"? During the scanner session, Did you happen to notice the ambiant air temp and engine coolant temp read throught the sacnner? Bad info from either one of those can cause a hard start issue when cold. Good Luck!

 

Yes, I bought this truck from a twenty something surfer kid under the assumption it had a rod/main problem, but I had a smoker parts engine anyway, so I figured 200 worth of bearings and oil pump and the crank from the smoker and I would have a running truck. Turns out the flywheel was broke. I never heard the truck run before I bbought it. I didnt know of any other major issues but i planned on tuneup and water pump and so on.

The crank sensor is supposed to be bad and was replaced. I was not there when it was scanned, my **** retentive partner that cant leave anything alone was there. He and the guy with the scanner which is regularly updated changed the crank sensor and said the sensor needed to be programmed, which required a park or neutral signal from the trans and the truck be run up to 5500 rpm to set the sensor. The trans was giving a 2nd gear signal in every gear but low. It will only start when it is in park or neutral though, so the "bad" neutral saftey witch these two changed was still doing its job, which I argued about that with them. All they have done is throw another 300 dollars at it and it still isnt fixed.
I scoured this truck for pinched and chafed wires and found nothing. I have bought two computers from two different junkyards, both with a matching service number. Now today the damn starter drive overrunning clutch gave out on it, tot he tune of another 80 dollars. The truck starts hard but runs well with the original computer but has not started yet with either of the other two computers, but then again some dingdong was in there cranking away and pumping the gas, which is probably confusing the computer even further.
I am really about at the end of my rope with this stupid thing. I am so close to getting it to act right. Oh and the stupid thing still is stuck in 2nd with the original computer.
It has shifted 1-2-3 on a alley for me a few times.
My solution was to find the two wires required for a park signal and jump them out long enough to set this crank sensor, then address the shifting issue.

They can change parts until theyre wrenches wear out, or they can see it my way, trick this thing into thinking it in park, set the sensor(which sounds like a pantload to me, and a GM service tech I know) and get on with our lives. If I have to Ill put a 700r4 in this thing to fix the shifting.
Sorry if I seem frustrated but all this is getting to be a bit much

 

I think i would ask them to stop spending my money! I have never heard of a crank sensor being programmed. How is the truck going to start on the day it is born in the factory if you need a motor spinning at 5000! If I saw someone rev my engine up to 5500 rpm I would kick their butt! In my opinion they arent doing you any favors. Back in 98/99 gm had trans issues where the trans was stuck in 2nd gear. It isnt a computer issue. But it does throw a code to tell you what is wrong. Deep breath. Think before you act. Sounds like the other guys just want to guess at problems and throw parts at it until the accidently solve the problem! Good luck!