Hot Rod Forum banner
1 - 9 of 9 Posts

·
Registered
Joined
·
37 Posts
Discussion Starter · #1 ·
Took everyone's advice.. swapped all the sensors from a running 350 tbi motor (ignition ESC, knock sensor, computer and prom) well.. it idles not bad, then it almost has a faint stutter, then when I stick it in drive it stalls..I've tried the timing to 0 wire unplugged.. no help..... allso it doesn't seem to advance timing when the wire is unplugged.. you think it would pick up or stall.. but only has about 1 inch either way and it acts up.. It has a th350 4x4 tranny in it.. I am wondering if it had a stall converter in it ?.. it came out of a carb 350 truck.. Any advice on why the idles slightly picks up then has a stutter and picks back up would be great.. Could it be I have the distributor out a few teeth ... Merry xmas :)
 

·
Registered
Joined
·
838 Posts
Sounds like a throttle position sensor with a dead spot.

Do you have a scan tool? If not hopefully you have digital volt meter.

You can probe dark blue wire on TP sensor. With key on, slowly open throttle while observing meter reading. Voltage should be less than 1.25 at idle position and about 4.5 volts at WOT.
Dark blue is signal to computer.
Gray wire should be 5 volts.
Black is a ground.


Timing is supposed to "lock" when set timing wire is unplugged.

A high stall converter would just allow engine to rev higher before it starts to apply torque to start turning input shaft. I dont think that has anything to do with problem.

Are you 100% sure your computer has the right prom and calpack for a 5.7L?

Has base idle speed cap been removed from throttle body where someone could have misadjusted it?

What color in the connector on your computer?
Black is an ECM that requires a spark module for knock sensor. Brown is a PCM it has spark module built into it, reads directly from knock sensor. They each use a different knock sensor.
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #3 ·
all came of 1987 Suburban

I took the knock sensor, ecm, throttle body with all sensors on it, form the above said vehicle. It ran before I pilled all this stuff... ran fine. I'll try changing the throttle position sensor.. Thanx for the advice
 

·
Registered
Joined
·
838 Posts
Oh man you are doing something that is very bad!!! :nono:

By just swapping stuff you are hoping to find a problem and replace it with a silver bullet.

What if there are 2 problems at once? Or 5 problems?? :confused:



On electronic controlled engines it is much better to diagnose each part good or bad. Replace if necessary, or eliminate it as a possibility and move on to something else. Eventually there will only be the problem left even if you have to test every single component on engine and wire in vehicle.

Knowledge of how each system works and what it does will help determine what to test and not test so checking every single part should not be necessary.
Human caused problems can be a lot tougher to track down. Especially if you have to find your own mistake. Even with a perfect operating computer system one of my problems was an internal engine problem that was caused by me.


I had to learn just like youre doing now, never touched a computer operated engine to be told go make that run on dyno with this here pile of wires and computer stuff. Good luck.
Started out with no manuals, no instructions, no scan tool, no meters, nothing except a soldering iron. I screwed up every way possible before figuring out there is no "silver bullet".
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #5 ·
How is that wrong..

I buy a good motor (minus intake tbi style), take all the sensors off a running engine with no check engine light on. I have all these parts and all are doing the same. I don't see how that is a bad way to do things.. Kinda hard to diagnose a problem when the check engine light gives no codes.. I am on here asking advice hoping someone has ran into this. If you know of a better way to diagnose this problem ..feel free to tell me. I can use the volt meter to check what you said, but you'd assume the check engine light would be on if there was something wrong.. I'll use the volt meter and see.. I just find it odd.. I have 305 parts on it, ecm , knock sensor , ESC and it run no different then when I was "advised" to replace it all.. I am going to checkwhat you said, then pull the plugs and find out if I am out a toth in the timing , TO date.. I have bought new plugs, wires, ESC by wells, cap, rotor. Replaced all the stuff I was "suppose to " to make it run. BUT when you start a vehicle, and it runs awesome for `1 hour.. THEN put those parts on your truck.. they should run the same. Pulling parts of vehicles and not testing them would be a no no.. not the other way around. My ecm is black plug ins bothe sides as are the 305 ecm's I have. To be honest.. the damn thing ran better when I had the other knock sensor in it from a 305

I do appreciate your advice.. this thing is frustrating me.. but you know what.. the next step is to finish the body stuff and drive it to a garage to have it checked out.
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #6 ·
well took your advice

Looked at the tpi, but couldn't get any readings as it was dark and I couldn't get my pointed ends to make contact .. so I checked the wires and firing order.. stupid me had 5 and 7 backwards.. I swapped em around and it ran AWESOME for 10 min.. I shut it off did some clean up and retried the truck.. WELL.. the POS now revs up and down.. not high revs like example 800rpm idle.. to 1100 back to 800 etc. I looked for air leaks but the tbi sucks so much air I can't tell.. Could the throttle body be over tightened .. I changed it to the 350 without a torque wrench.. it seems like a vacuum leak but I just don't know anymore.. I unplugged the TPI sensor while idling and it makes no difference My ecm has this number on it

Service number 1227747
869931 M720015136

I pulled this from a 350 87 suburbon and the knock sensor / esc and the Suburban ran awesome.. so I am lost. My distributor is out as I have the wires 2 spots ahead in a circle from where they use to be.. so I am going to roll the engine to top dead center and drop the distributor back in. If anyone has any advice PLEASE let me know.. I have no check engine light on or anything.. Funny thing is it idled when the firing order wass wrong, but not when I put it where it was suppose to be.. thanx
 
1 - 9 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top