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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: 02/24/14 07:26 PM

Brian

I was reading this post because im having the same issue with my 89 tbi 350 suburban. It runs great drives great has all power starts right up, But once its warmed up it will just die when i put it in reverse or drive but only at an idle. I can keep it going by getting to the throttle real quick. But only when its warm it will idle in gear just fine till it warms up.

So here it goes iv replaced the iac, o2, ignition module, temperature control, plugs wires cap and rotor, map sensor, fuel pump relay, fuel filter, the fuel pump and strainer along with the tps were changed 2 years ago.

I have 12 psi fuel, And i have set the timing to 0 tdc with the wire unpluged and set the base idle following the procedure because the guy before me had messed with the screw and timming. The burb only has 108k original miles.

I really need some help. This thing is about to go of a cliff  

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codman4x4
I love my Chevy Chevette!
Posts: 10
Joined: 02/14
Posted: 02/24/14 07:29 PM

Brian

I ment to say only when its cold it will idle in gear just fine until it warms up  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 02/24/14 10:55 PM

welcome code man...   brian has not logged in for 14 months. so its probably fixed..

i am still around with a slightly different user name..

coolant temp sensor SU102.. did you change this.. its right up front on the intake manifold..

Su102

like i ask brian to perform..

can you with the engine off..  grab the throttle lever.. open it slightly.. see if there is any movement front to back where the shaft goes thru the throttle body..

good... (O)  

bad. ( O)  or (O )  


find a scan tool..  see if the live data is within spec..

190 to 215F from the scan tool
over 0.50 TPS voltage.. but below 0.98 volts..
IAC.. between 20 and 50..

or else..

take a screw driver and a shop towel.. wedge it into the idle air control triangular opening next to one of the mounting bolt heads..  block the air flow..

the engine should just barely running. 500 to 550 RPMs..  you can use the T15 idle stop screw to adjust it ..  but if there is PLAY in the throttle shaft. you could adjust for months and it still is not going to idle properly..  it will be too fast.. or too slow..  and this is the fault of the wear..  it keeps changing the TPS voltage when the throttle closes..  if its not the same each time.. you will have an unstable idle..   if its lands below the previous voltage set.. it will reset to that lower voltage.. but if it lands above that lower voltage it will think that you have your foot on the gas and will keep the fuel injector pulse width wide and pour in the fuel at idle..  

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codman4x4
I love my Chevy Chevette!
Posts: 10
Joined: 02/14
Posted: 02/25/14 04:39 PM

Wayne thank you for the reply.

 I have replaced the cts along with the others.

I have also checked the throttle shaft and there is no side to side movement.

Today i was messing with it and when i would unplug the tan wire with black tracer that you unplug to time the motor it would run perfect. It was a nice low idle and would not die in gear even when it was warm.

so im guessing somthing is telling it to advance to much.  

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codman4x4
I love my Chevy Chevette!
Posts: 10
Joined: 02/14
Posted: 02/25/14 04:39 PM

Wayne thank you for the reply.

 I have replaced the cts along with the others.

I have also checked the throttle shaft and there is no side to side movement.

Today i was messing with it and when i would unplug the tan wire with black tracer that you unplug to time the motor it would run perfect. It was a nice low idle and would not die in gear even when it was warm.

so im guessing somthing is telling it to advance to much.  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 02/26/14 12:52 AM

throttle shaft play is not side to side.. its front to back..  with the throttle part way open..  because the throttle lever pulls backwards.. the TV cable pulls backwards on the bottom of the lever and the spring is on the bottom rear..

like this..

Wornbushing Zpsf56c0607

Tbirebushing Zpsd21260ba  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 02/26/14 01:25 AM

please refer back to the ignition system testing..

see if the reluctor magnet is cracked..  or the pickup coil magnet is cracked..

it will car a misfire except when the tan and black bypass wire is disconnected..

because over 400 RPM.. the system is in Electronic spark timing mode..

where the ignition module starts a timer when the pulse trigger happens..  the EST and PCM/ecm change the count down timing.. make the count shorter and the timing advances . make it longer and the timing retards..

this whole thing requires equally spaced signals from the pickup coil and the reluctor interaction..

when the magnets crack. the sine waves out of the pick up coil windings have GHOST patterns in them.. this throws off the electronic spark timing..   causes random sparks to be created..  makes for some odd running engines..


take a timing light.. hook it over each spark plug wire one at a time..  see if you are getting nice even flashes.  if you are getting random sparks.. on some.. or on all of them.. its time to pull the cap and inspect the pickup coil and reluctor..

Smallcapheicracks

if you happen to have a large cap HEI...

Untitled5 Zps63341c9b

Untitled3 Zpsb7fb0c42


you should also make sure that the wiring coming out of the distributor base.. and over to the little box on the firewall is not next to the high voltage spark plug wires..  the signal voltage is around one volt.. the high voltage spark voltage can easily be 40KV and just the magnetic field around the spark plug wires is enough to cause issues..  

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codman4x4
I love my Chevy Chevette!
Posts: 10
Joined: 02/14
Posted: 02/26/14 04:08 PM

Wayne thank you again.

I will get right on that and report back.  

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codman4x4
I love my Chevy Chevette!
Posts: 10
Joined: 02/14
Posted: 02/26/14 04:31 PM

Wayne thank you again.

I will get right on that and report back.  

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codman4x4
I love my Chevy Chevette!
Posts: 10
Joined: 02/14
Posted: 02/26/14 07:21 PM

Wayne

Ok so i checked the spark plug wires and they were touching the low voltage wires so i rerouted them. That did help the response of the motor but did not fix the problem.

I checked the magnets on the coil and cannot see any cracks at all.

But i did find it interesting that, when i would grab the dist shaft i could move it up and down and the pickup coil would spin a little. I'm not sure but i didn't think there should be that kind of play.

I don't have access to a timming light today but will tomorrow so i didn't get to check for the ghost signals like you asked.

To refer on the the throttle shaft. I cannot hardly move it what so ever.  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 02/27/14 12:27 AM

vertical motion of the distributor shaft is expected...

aluminum housings expand more than steel distributor shafts..

if there is not play when the distributor is below normal operating temp of 192F to 230F.


please... also.. watch the damper with the timing light..  see if the timing jumps all over the place.. randomly.. withe transmission in park..   and then again.. with it in drive..


if you can... pull any check engine light codes...


ir you are really lucky.. please go back and print the TBI live data chart i posted..

write your numbers down at idle..  and also at 25 or 30 miles per hour..

some scan tools can record the live data stream..

post those numbers...  

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codman4x4
I love my Chevy Chevette!
Posts: 10
Joined: 02/14
Posted: 03/01/14 06:34 PM

Wayne

So i went back to your pics that you posted for me and realized that i was looking at the reluctor and pickup coil wrong. The magnets are cracked and the were pushing upward like they were getting squeezed and i could scrape them off with my fingernail.

So i am putting a new dist, and coil tomorrow. so i will let you know how that goes and if it fixes the problem. I'm positive it will  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 03/02/14 02:25 AM

do your self a HUGE favor...

when you have the replacement and are ready to remove the old distributor..

take off the CAP only..  leave the rotor in place.. note the location of the wire that goes to the #1 spark plug on the cap..

use a 7/8" or 15/16 socket on the alternator pulley nut.. you should be able to rotate the engine in a normal clockwise direction at the alternator.. looking at it from the front..  until the rotor is pointing in the direction of the #1 wire location..

now.. look closely at the reluctor teeth and turn the crank to align the reluctor teeth with the teeth in the pickup coil..  

look down at the damper..  the base timing mark as described on the timing label should be lined up..

guess what you can remove and reinstall the distributor.. once you get the oil pump drive shaft engaged.. you can turn the housing to align the pickup coil with the reluctor teeth and lock the distributor down.. make sure its fully seated on the oil pump shaft...

i do this.. and i can preset the engine.. take the distributor out and work on it.. drop it back in.. get it seated on the oil pump shaft.. turn the housing to align the pickup coil and reluctor and lock it down.. reach thru the window and start the engine on the first try..  people think i am an amazing mechanic..



take some pictures.. post them to photobucket.. lets see how bad your parts are..


don't forget.. the reman parts may look different..  the one with the sintered reluctor instead of a stamped steel reluctor is a far superior design..  

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codman4x4
I love my Chevy Chevette!
Posts: 10
Joined: 02/14
Posted: 03/02/14 08:40 PM

Wayne

I replaced the dist.. today and everything went great. I go it all back together just right and it ran amazing. i got it base timed and it was perfect the idle lowered it was 800 in park and 600 in gear didn't die while in gear anymore. I was so happy.

But i took it for a short drive and everything was great, so i decided to take it for a trip to my dads which is 60 miles round trip. But on my way there it seemed like it lost some power cause i was having trouble keeping it at 60 mph up even the slightest hill. When i got to my dads the motor was running kinda rough, it wasn't stalling just kinda rough along with not very responsive with a little pop in the exuast.

so im not sure were to go from here.  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 03/02/14 09:08 PM

recheck timing..

verify the spark plug wires are ALL FULLY SEATED AND LOCKED DOWN into the cap..

verify the spark plug wires are all LATCHED onto the spark plugs...

verify the spark plug wires are not laying together and crossfiring.

use your timing light if you have it with you.. on individual spark plug wires to verify a single flash on each wire..

examine the inside of the cap and the rotor... for signs of carbon tracking..


you might also want to look at the coil.. do it at night if you don't freeze. you might see little purple sparks.. causing issues.


a cranking compression test.. where you have unplugged the 4 wire connector at the distributor.. that will shut off the ignition and the fuel injection..

crank engine and listen to cranking sounds from flywheel starter drive..

is it an even sound.. or does the engine speed up during one part of the rotation..


wrrrrrrrrrrrrrrrweeeerrrrrrrrrrrrweeeerrrrrrrrrrrrrrweeeerrrrrrrrr you get the idea.

if you have lost compression in one cylinder .. you will find that the engine cranks just a little faster when that cylinder comes up on the compression stroke..


a little pop from the exhaust could be a burned exhaust valve.. a leaking exhaust manifold.. a blown out or loose spark plug.. a loose wire.. a cracked cap. a bad intake or exhaust rocker/pushrod/flat cam lobe..


just curious.. does that have a vacuum operated trap door at the back end of the right hand exhaust manifold.. i don't recall what year they stopped those..

if the vacuum hose fell off and it lost vacuum.. the trap door will slam shut and force most of the exhaust thru the passage under the intake. i just don't recall what year they stopped it..  

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