Bad stumble

[graham1524]

Got the timing set and the truck idles perfect. ran great in the driveway so i took a slow and easy road test to see if it was good, but when i gave it gas it would stumble ridiculously.

I replaced the oil pressure sending unit and had to remove the distributor while it was apart i added the silicone vacuum line kit and now its all back together and idles but wont really go. Any suggestions on what it could be? it ran great before i had to replace the sending unit.

 

[berzerker]

Re: Bad stumble

go back thru your ignition wires .. firing order and wire connections. got an wire switch around to the wrong cylinder.

 

[graham1524]

Re: Bad stumble

All the wires are correct and i was reading another thread that said to take off the O2 sensor but it would not start with the sensor unplugged

 

[bezerk]

Re: Bad stumble

have you set it with the tan wire disconnected?

 

[graham1524]

Re: Bad stumble

Yup tan wire disconnected the whole time then turned it off and started it again

 

[4C FED]

Re: Bad stumble

Pinched hose to the map?
One time when I was working on mine I inadvertently trapped the hose between the map and the clip mount. Terrible stumble but it idled fine.

 

[graham1524]

Re: Bad stumble

Checked all the vacuum lines and the charcoal line was pinched so i got it unstuck and it nothing same thing still. but i did notice that now the fuel pump primes for alot longer than it used to and even after i turn off the truck how do i check to see if its fuel pressure or fuel related ?

 

[graham1524]

Re: Bad stumble

Did the bike tire vacuum leak test and think i found the issue theres a big leak on the front of the throttlebody where the throttle is but i dont see where the leak is. Can anyone point me to where it could be leaking from I really don't want to get into this without some help from someone who has a better idea of whats goin on with my truck

 

[4C FED]

Re: Bad stumble

Worn out throttle body. It leaks around the throttle shaft. You need to do a Matt Blum rebuild.

 

[graham1524]

Re: Bad stumble

Thanks I'll be looking in to that

 

[graham1524]

Re: Bad stumble

Could that be the reason the truck idles fine and almost dies under any acceleration? or would that be another problem

 

[4C FED]

Re: Bad stumble

I wouldn't think so.
Usually creates a crappy idle (not steady).

 

[graham1524]

Re: Bad stumble

Went to auto-zone and got a map sensor that did the trick it runs great again.

The guy at the counter was like a syclone whered you get one and i said my uncle and he was like whoa theyre all the rage in Japan and now people are importing them here. I just kinda looked at him like yea its American made but didnt correct him and left.

 

[graham1524]

Re: Bad stumble

This thing keeps going went out today to start it up and once again hard to start and stumble like crazy even after it ran perfect the other day. So is there anyway it could be killing the map sensor or i just havent found the real problem yet?

 

[Quickstop [UK]]

Re: Bad stumble

Checked all the vacuum lines and the charcoal line was pinched so i got it unstuck and it nothing same thing still. but i did notice that now the fuel pump primes for alot longer than it used to and even after i turn off the truck how do i check to see if its fuel pressure or fuel related ?

mech FP gauge off the rail? stock truck is at 42 psi once you prime it.

Should only be on for 2 seconds. Take off your oil filler cap and smell for gas. You might have leaky injectors.

Does the fuel pressure stay high once you turn the engine off?

I found out the other day ithat if you have a bad leak on your injectors, you can unplug the FP relay (2nd from the right looking from the front of the truck to the firewall - grey and orange wires in it) and then start it up. If it idles for a bit then you have some leaking injectors.

Mine ran great for a minute or two until I opened the throttle and then the engine ran out of gas. You might have something similar. If it sounds like it is trying to start then you have fuel in the cyl = leaking injector.

When you give it gas, the FP rises and the cylinder gets flooded - gas in the oil hence smell for gas.

Might be your issue. Prob not though but it's a 2 minute check.

 

[graham1524]

Re: Bad stumble

mech FP gauge off the rail? stock truck is at 42 psi once you prime it.

Should only be on for 2 seconds. Take off your oil filler cap and smell for gas. You might have leaky injectors.

Does the fuel pressure stay high once you turn the engine off?

I found out the other day ithat if you have a bad leak on your injectors, you can unplug the FP relay (2nd from the right looking from the front of the truck to the firewall - grey and orange wires in it) and then start it up. If it idles for a bit then you have some leaking injectors.

Mine ran great for a minute or two until I opened the throttle and then the engine ran out of gas. You might have something similar. If it sounds like it is trying to start then you have fuel in the cyl = leaking injector.

When you give it gas, the FP rises and the cylinder gets flooded - gas in the oil hence smell for gas.

Might be your issue. Prob not though but it's a 2 minute check.

Checked the oil cap and it does smell like gas and after i cut it off the fuel pump primes again. will look into it more this weekend

 

[graham1524]

Re: Bad stumble

mech FP gauge off the rail? stock truck is at 42 psi once you prime it.

Should only be on for 2 seconds. Take off your oil filler cap and smell for gas. You might have leaky injectors.

Does the fuel pressure stay high once you turn the engine off?

I found out the other day ithat if you have a bad leak on your injectors, you can unplug the FP relay (2nd from the right looking from the front of the truck to the firewall - grey and orange wires in it) and then start it up. If it idles for a bit then you have some leaking injectors.

Mine ran great for a minute or two until I opened the throttle and then the engine ran out of gas. You might have something similar. If it sounds like it is trying to start then you have fuel in the cyl = leaking injector.

When you give it gas, the FP rises and the cylinder gets flooded - gas in the oil hence smell for gas.

Might be your issue. Prob not though but it's a 2 minute check.

Got a fuel pressure guage installed and when it primes reaches almost 20 psi then drops to zero in about 2 seconds

probably leaky injectors? how to test?
could the vacuum lines be wrong?

 

[Big Mike]

Re: Bad stumble

Check the throttle body again for the big vacuum plug pointing towards the egr valve, it may be cracked also do you have the correct pcv valves in the truck I would try to get the GM or Ac Delco ones GM #8995910 AC Delco #799C with letter "E" on bottom? What is your fuel pressure when truck is running, is it at least 42lb? Have you checked for vac leaks using 2+2, spray around gaskets to see if your idle changes.

 

[graham1524]

Re: Bad stumble

Check the throttle body again for the big vacuum plug pointing towards the egr valve, it may be cracked also do you have the correct pcv valves in the truck I would try to get the GM or Ac Delco ones GM #8995910 AC Delco #799C with letter "E" on bottom? What is your fuel pressure when truck is running, is it at least 42lb? Have you checked for vac leaks using 2+2, spray around gaskets to see if your idle changes.

Just put in new silicone vacuum kit. Won't start only has like 18 psi on fuel while cranking. It ran great before replacing the vacuum lines and taking the distributor out to put in the oil pressure sensor if that would cause anything.

 

[SloGN]

Re: Bad stumble

Just put in new silicone vacuum kit. Won't start only has like 18 psi on fuel while cranking. It ran great before replacing the vacuum lines and taking the distributor out to put in the oil pressure sensor if that would cause anything.

graham

it sounds like your fuel pump has taken a crap.