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1989 GMC SLE TBI 350 5.7 Runs terrible when hook to computer

 
codman4x4
I love my Chevy Chevette!
Posts: 10
Joined: 02/14
Posted: 03/03/14 02:19 PM

Wayne

Ok so bone head move on my part. I was so worried about the plug wires touching the low voltage wires that i completely overlooked my #6 wire laying on the exaust manifold so it melted and was grounding.

So got her fixed and everything is awesome.

Thank you for your time and all your help you have saved this burban from rolling off the cliff.  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 03/04/14 01:06 AM

i am so glad to help..  there is nothing better than a sweet running motor..


here in hollywood.. there is a road called Mullholland Drive..  runs along the top of the hollywood hills from the hollywood freeway all the way past malibu..

there is one curve up there where cars with their drivers kept going over and crashing to the bottom of the canyon.. one guy was found 5 days after going over.. on top of another car whose driver had been missing for 10 days..  that guy did not make it..   i called the city council office for that area.. ask them to install guard rails to stop cars from going over and to clean up the cars that are left down there. the staff member that i was talking to went into a rant about how long mullholland is.. and they cannot afford to install guard rails all the way along. i said.. just where cars have repeatedly gone over..  he replied.. how will we know where will we find that info.. i said.. ask the fire department. the highway patrol, the lapd,  the tow truck drivers..  they are all involved when a car goes over..  about 2 weeks later.. they made an announcement that the cars are all being recovered by a towing company.. and guard rails in dangerous curves are being installed..  i just smiled.. and a twist.. if you watch 2 and a half men... in one episode charlies mom returned his benz after she made out in the back seat.. charlie said. don't return it.. just push it off a cliff i don't want it back..

whats really funny.. is somebody stole charlies real S class benz and pushed it over the cliff..  not once. but a second time after it had been repaired.  charlie lives on the north side of mullholland drive.. in ENCINO. actually..  so .. see i don't just help people on the forums.. i help people in real life also. i just sit here and smile..  

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ihatespamman
I love my Chevy Chevette!
Posts: 5
Joined: 03/14
Posted: 03/04/14 09:00 AM

Hi Wayne, I'm hoping you can help me now. I have an older chevy that I've grafted a TBI onto. I have a throttle body off a 92 p/u 350 and a computer from a 92 Caprice 305. I cannot get it to idle smooth. It will fire right up and run smooth for a minute until it starts looking for the o2 signal. Then it will start stumble, almost stall and then surge really bad, smooth out for 10 or 15 seconds then do the same thing. It'll do this 4-6 times before it will finally die. It will start right back up and go through the same cycle. If I unplug the o2 it runs like a top. I have changed to a 3 wire sensor and that didn't help much. I've got an adjustable regulator and am running about 14 psi. What would you like me to look for? Any help is greatly appreciated.  

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ihatespamman
I love my Chevy Chevette!
Posts: 5
Joined: 03/14
Posted: 03/04/14 09:01 AM

Hi Wayne, I'm hoping you can help me now. I have an older chevy that I've grafted a TBI onto. I have a throttle body off a 92 p/u 350 and a computer from a 92 Caprice 305. I cannot get it to idle smooth. It will fire right up and run smooth for a minute until it starts looking for the o2 signal. Then it will start stumble, almost stall and then surge really bad, smooth out for 10 or 15 seconds then do the same thing. It'll do this 4-6 times before it will finally die. It will start right back up and go through the same cycle. If I unplug the o2 it runs like a top. I have changed to a 3 wire sensor and that didn't help much. I've got an adjustable regulator and am running about 14 psi. What would you like me to look for? Any help is greatly appreciated.  

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ihatespamman
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Posts: 5
Joined: 03/14
Posted: 03/04/14 09:28 AM

Oops, I hit the reply button twice. Anyway, I went back and double checked the grounds and found that the battery to block was .004, battery to body is .004 and body to block is .008. Is that an issue?  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 03/04/14 03:17 PM

IhateSPAMman
test 2 at 0.04 or 0.004   either would be OK
test 3 at 0.04 or 0.004   first is too much . second is OK.
test 4 at 0.08 or 0.008   first is too much.. second is OK.

0.08 is 8/100ths
0.008 is 8 1,0000ths..

4/100ths on test 2 is ok
2/100ths or less on test 3 or 4 is ok..
how is the ground connection on the stud at the thermostat housing.?? or where ever you have connected it..  check the wires into the crimp connector to the engine .. that should read close to 0.01 or less in 2 volt scale.

Tbi Ground Zps2317f7aa

GM TBI Intake Zps9153bfce


GM TBI Settings Zpsd5b05066

if the base idle is too slow.. it can surge and die.

disconnecting the Oxygen sensor puts the system into OPEN loop..

ignition distributor inspection also.. as described above..  this effects both large and small cap HEI's  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 03/04/14 04:43 PM

another question..  do you have any exhaust leaks????

is the air injection system properly hooked up?? or blocked so no UNCOMMANDED air is allowed to enter the air injection system or exhaust???


what happens when air is sent in after the computer drops into closed loop and its setting the air fuel mixture on the oxygen sensor feedback..

dilution of the exhaust stream past the first oxygen sensor causes the fuel system to spray in more fuel..

if there is a significant air leak or exhaust leak. there will be enough extra oxygen and fuel that it will melt the cat monolith

if your volt meter measures Millisecond. MS..  you can look at the fuel injection pulse width...
1.2 to 1.4 Milliseconds at idle in closed loop

if its not in idle fuel trim.. you may find 2.1 to 3.4 Milliseconds of injection pulse width  

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ihatespamman
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Posted: 03/04/14 09:19 PM

Thanks for the info. I didn't pay attention to amount of zeros after decimal point. I will double check those figures.

As I said, It's "grafted" onto the motor. The truck is an 83. I didn't build the motor that's in it but it is not anywhere near original. It is a 350. has a mild cam. No idea what cam because I didn't build it. Dual plane "performer" style intake. No Egr or AIR system. Headers into a single 3" exhaust. No cat.

I have an adapter plate that bolts to the manifold where the 4 bbl would have mounted and the throttle body bolts to that. I have ecm ground attached at one of the adapter mounting bolts. Should I move them to the t-stat bolt? It's only about 2" away. The throttle body has no movement front to back. The TPS is at .98. I've checked that numerous times. I've reset the IAC a number of times as well by grounding the ALDL method. I check the TPS every time I've done that. There are no leaks in the exhaust.  

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ihatespamman
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Posted: 03/04/14 09:31 PM

I went to my friend's house that has a proper scan tool this evening. As the surging got worse, he block learn got lower and lower until it stalled. We took this to mean that it's running too rich and decided to lower the fuel pressure. I was running at 15 lbs. after we got it adjusted down to about 13 it really smoothed out. The integrator sat at 127 and block learn stayed pretty steady between 120 and 125. BUT, when I took it for a test drive I got code 44 - lean. Raise the pressure, it runs fat at idle, lower the pressure, runs lean on the highway. Would higher volume injectors, like the 65 lb cop car ones, maybe help that?  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 03/05/14 12:01 AM

look at the throttle body picture.. lower the TPS voltage..

i have been looking for the proper TPS voltage.. looks like it's slightly below where you set it at..

when it gets to that voltage.. it converts from a nice lean idle.. to idle transition and richens up the injector pulse width..

C4 L98 TPI motors need the throttle position voltage to be exactly 0.53 volts.. no more.. no less.  or it just won't run right..

Tbiminimumidlesetting Zps14faef45


IDLE Aircountstbi Zps0a49788f  

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KeyWester
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Posted: 04/03/14 09:13 AM

WayneP- I'd like to get your advice on where I'd should go next with a 1989 GMC P3500 stepvan I'm trying to bring back to life. Here's the basics- the vehicle sat for about 3yrs- I got it started after cleaning the cap and rotor and was able to limp it to where I could work on it. After dealing with cooling and brake issues, It needed a new battery and alternator before I could get around to the rough running. First thing was a new fuel filter, it then started, idled and rev'd good, Started an hour later, still OK... started a couple more hours later, wandering idle, wouldn't rev. so over the coarse of the next few weeks it received, not necessarily in order, throttle body kit, cap, rotor, plugs, plug wires (in the correct place), distributor (magnet cracks), IAC, EGR, ESC, Knock sensor, MAP, compression @ 150-160psi all 8cyl, cleaned valve cover vents both sides, cleaned breather hose, PCV, damper timing mark @ 0 degrees w/ reluctor tips lined up and rotor pointed @ #1cyl, vacuum hose all checked. So after replacing all that, here's what it's doing, it hates being set at 0 degrees, stalls & won't rev. Rotating cap to where it runs takes the damper mark to where you can just see it approaching the timing marks. Here's how I can repeatedly get it to run/drive ok. Start it with the MAP vacuum hose removed, wait 5 sec for computer to intervene and go into what I guess is a pre-programmed mode, I get a good/slightly high idle & good revving, but stalls when put into gear. So when it's in this mode, reattach MAP vacuum hose, vehicle runs/drives OK. It takes 3 or 4 attempts in the morning when cold, 1x when the engine is warm. I'm at the point where I want to replace the computer. I get codes whenever I disconnect MAP or ignition tan/blk wire, can erase them, get 1-2 code all other times. I believe I've replaced good modules already & know that computer replacement might be a wasted step. So... have you any advice? Thank you in advance.  

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KeyWester
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Posted: 04/03/14 09:16 AM

another thing, grounds have all been cleaned and treated w/ dielectric grease  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 04/03/14 10:08 AM

stalling when you put it in drive could be several things..

since you don't have a scan tool to look at live data..

perform the info on this image..

start with the RED TEXT.. check for throttle shaft play.. i have a fix..


if there is no play then perform the base idle setting in black or if you had a scan tool in white..

GM TBI Settings Zps77e97d79


or follow these instructions..

Tbiminimumidlesetting Zps14faef45

IDLE Aircountstbi Zps0a49788f


this is where to start...

you might also want to take the Computer ground connection off and clean it.. take the stud out and clean that.. reattach ..

GM TBI Intake Zps521dbcb6

Tbi Ground Zpsd6814a4c



test your TPS voltage...  

Tpsvoltagecheck Zps726b55d5  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 04/03/14 10:19 AM

i guess you have covered most of that...

do you have a digital volt meter..  

hook up to the oxygen sensor with the meter in 2 volt AC mode.  take the engine rpms to 2500.. and let it stay there for 15 seconds..  see if the oxygen sensor voltage goes from 0.01 to 0.9 volts.. not a steady flat line.

if you get a steady flat line.. especially at idle.. lets look at your air injection system...

unplug the hoses going into the check valves into the exhaust manifolds..  not the converter...    plug the hoses going into the check valves.. so no air leaks into the exhaust stream...  plug one of the open hoses from the diverter valve you just disconnected.. so you only have one air outlet. . you should only have airflow for the first 20 seconds..  what happens is the diverter valves can fail.. dump uncommanded air into the upstream system and fool the oxygen sensor into screwing up the air fuel ratio...

i can describe how to test the diverter valve if you have one..  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 04/03/14 10:24 AM

lastly.. find the fuel pump fuse in the fuse block..

either pick up the circuit tester from harbor fright that plugs into the fuse block and measures amperage.. or hook up your digital volt meter in 10 amp or larger setting.. some have 10 amp.. or 15 or 20 amp DC  settings.. monitor the fuel pump current..  make sure its not over 7.1 amps..  

you might also want to perform the voltage drop test..

Voltagedroptesting

with an additional test from the negative battery post to the frame rail in 20 volts DC setting first.. then in 2 volts DC..  0.02 volts would be ok..  the fuel pump is grounded to the frame rail..  the frame rail needs to be grounded to the battery negative..  

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