vortec 350 issues (1 Viewer)

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simpson110

simpson110

Joined
Jun 7, 2012
Threads
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30
Location
Ct
just finished putting a vortec 350 in my 76 fj40, for the most part everything worked out great but i am having some issues with how the motor is running and cant seem to find a straight answer anywhere.

my issue is when i have my tps plugged in i get a really bad stumble off idle if i tab the throttle, it will even stall completely if i hold the gas down. if i feather the gas the rpms will raise normally until about 2500 rpm, then it starts to stumble again. with the sensor unplugged, issue is gone, motor runs like a champ. only issues with it unplugged are CEL(check engine light) and has a hard time settling into an idle running off the map sensor.

so i replaced the tps with a new acdelco one because i eventually get a cel for the original one. problem still there with the new sensor, no change at all. i check the voltage on the sensor, .6v at idle and 4.6 at wide open throttle. i have cleaned the maf, and also checked fuel pressure, which is 57psi at idle and 65-67psi when i hit the gas. i upgraded to a mpfi delphi spider before i put the motor in the truck.

i was searching around to see if anyone has had this issue before, and i saw that pretty much everyone that runs these engines(any vortec really) ends up running the vss and i dont have that hooked up right now. if thats my problem i have found the jtr reluctor ring kit that seems to be the answer. i had my computer and harness done by jims performance and he is very helpful, but can only help so much over the phone.

if anyone has had this issue, please let me know how you fixed it, this is the last thing i need to figure out so i can start driving my fj again.
 
Make sure you have the O2 sensors connected per the OEM manual or the drawings on LT1Swap (same as OEM). I had some issues and had been using a drawing from the AutoZone site (for it's single-page convenience). The AutoZone schematic labels the O2 sensors #1, #2, #3, and #4, but they are not Bank1Sensor1, Bank2Sensor1, Bank1Sensor 2, and Bank2Sensor2 as I expected. I initially had the front O2 sensors swapped (the rear sensors are programmed out). Check your O2 sensor connections. O2 wiring for 96-97 shown below. 98-99 can be found at LT1swap. http://lt1swap.com/1999_vortec_5.7/index.htm

VSS is not your issue. VSS only matters to an auto tranny for shifting or for idling down the engine when you're slowing down (like at a stop sign). I built my own VSS and it works fine, but it really only comes into play when you're driving.

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thanks, ill take a look, but i only have two o2 sensor connectors. the secondaries were removed by jims performance when they re worked the wiring harness. i will still make sure i have the right ones there.

i just got off the phone with jim from jims performance and he is sending me another ecu to verify that the ecu is not the problem.
 
I eliminated the rear O2 sensors also. All they do is monitor catalytic converters and let you know when they're failing. I don't have cat converters.

With the O2 sensors crossed, my engine idled OK, but stumbled during acceleration and would not run past 2000-2500 RPM. The PCM was dumping fuel to the side running rich and starving the side running lean. Runs like a top now that I have the two sides hooked up correctly. That sounds a little like your issue.

Good Luck.

simpson110 said:
thanks, ill take a look, but i only have two o2 sensor connectors. the secondaries were removed by jims performance when they re worked the wiring harness.
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Checked the o2 sensors and seems everything is in order, assuming bank 1 is driver side. If that not the case then they are swapped but I'm not really sure that's the issue because it seems to run pretty good without the tps plugged in.
 
Yeah, bank 1 should be driver side.

Which year do you have?

simpson110 said:
Checked the o2 sensors and seems everything is in order, assuming bank 1 is driver side. If that not the case then they are swapped but I'm not really sure that's the issue because it seems to run pretty good without the tps plugged in.
Click to expand...
 
Out of a 99 I believe, and the harness and computer are the same year as far as I know. I know I needed the vats removed so at least a 98 computer
 
VSS is going to have to be functional or you will have intermediate stalls and less power, a good bit less power. Don't know why the issue with the TPS. i have not cats, no EGR, no rear 02 sensors, do run VSS, no fuel tank pressure or evap stuff.

Assume you have no active codes in the PCM at present? Also assume your PCM is programmed to know that you have various sensors missisng?
 
Right, ecu programmed for bare minimum engine management only. No codes present at this time. I should have another ecu in a few days, at this point it seems like that is the only answer. It's like the ecu is getting the signal from the tps and using it in the wrong way.
 
using the GM engine harness or something else? I can tell you that you cannot use a 99 year model PCM with a Painless standalone engine harness. My engine is from a 99 Yukon. Some minor difference on the 99-98 year model PCMs... so have to use a 96-97 PCM with a Painless engine harness (5.7 Vortec) FYI... May not apply to you but might help others. Hope the PCM swap out fixes things.
 
Using a gm harness that has all the unnecessary stuff taken out. Thanks for the help so far guys, I'll keep you updated with new ecu. If anything else comes to mind let me know.
 
I had a bad map sensor one time on this same 5.7 vortec in modified state, did not set a trouble code, but engine ran like crap for no reason and would stumble and run extremely rich. I initially though injector issue but Mr. Good Wrench (friend of mine) saw the map data out of range on live scan tool, new map sensor fixed it. Those things kill you because they are crazy to track down, especially when they don't flag a trouble code.
 
I'm putting a jtr kit on my ls tomorrow. I foresee problems getting it to fit with the e-brake cable in the way. I got the one with the 4 pulse sine wave and toyota in and out so I can still run my analog speedo. It seems to run pretty great without it so far. I realize gen II and gen III vortec are different beasts though.

What vacuum are you getting? Is your base timing on? Iirc, that year vortec still runs a distributor.
 
Hey Elbert, Jim from Jim's performance was kind of thinking the same thing then just threw the whole idea out. I think I am going to pick one up just to see. Worst case I have a spare map sensor kicking around. It kind of sounds like a similar issue that you had.

Someday I will get the reluctor ring setup but right now I don't think it's really my issue. Let me know how it all works out with the jtr kit.

As for the timing and vacuum, timing is right on had that verified with gm tech2 and not sure on the vacuum but I have an old boost gauge kicking around so I'll check it today.
 
The jtr kit was a very tight fit with the e brake cable. It took some manipulation of the cable. It does work. My speedo works as well as it ever did and the PCM is getting a signal that is closer than I thought it would be. I'm about 10-12% slow. That's fine. The only problem I was having with no vss was a idle speed too high code. Now that it knows it's moving it should be fine. Again, gen II is different from gen III, but I replaced my MAP today too. It was reading 14.5 psi at idle, or about 2 HG/in. Pulled the plug and it went to 30 HG/in. Swapped it out and it reads 19.7 at idle now. It ran fine with the bad MAP.
 
Good to know with the jtr kit. I probably won't get one of those until I get the motor running better, and I don't have an ebrake so I won't have to deal with that issue when it comes time.

And I ordered a map sensor today just to try it of course they didn't have an acdelco one in stock at any of the auto stores near me(just about all of them, including a couple Chevy dealers). But will be here tomorrow morning.

Also, Jim didn't have a spare ecu, so I got another one, $40 shipped on ebay. I figure worst case a have a spare ecu with my tune for $50 after shipping sending to Jim.
 
The VSS should not really be an issue with engine performance issues with the truck not moving. But it sure is under movement. Remember the PCM has no way to "know" if the truck is moving except via the VSS, as I recall there are some factors the PCM looks to given speed or mph.
 
Ya I want to get it running decent at a stand still and then I will take care of moving issues lol. The vss has a lot more of an impact with an auto trans than a manual I would imagine, like spotcruiser was saying before.
 
Only if it's a computer controlled auto. Mine is not. Otherwise you'll see stalling problems more with a manual.

The PCM cares that the vehicle is moving so it doesn't try to adjust idle. the PCM backs out the iac at cruise trying to get down to 600 rpm and then can't adjust back fast enough when you push in the clutch. Other than ABS, traction control and cruise, and some OBD II monitors like evap the PCM doesn't use the vss much. It is helpful if it can see the vehicle is moving, but it doesn't care how fast.
 
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