89 burban 350tbi runs rough

[Jims86]

Alas, another thing...Was the Idle set on the new Throttle body with the Idle Air Control motor disconnected?
You have to jump A and B on the diagnostic connetctor, turn the key on for 30seconds(engine off), disconnect the IAC motor(square 4 wire plug) take the jumper out of A and B, start the truck, let it settle down for about a minute, and with a hand held tach, and the engine in drive, you want to turn the idle screw down until you get 500(+/-25)rpm, shut the truck off. plug the IAC back in. Disconnect the battery for 15 seconds to clear the memory, re connect, and go for a drive around town to let the computer re learn.
Note:The engine must be at operating temp, and the timing must be set to factory spec.(0*) befor performing the above proceedure.

 

[89Suburban]

I love watching Jimmy in troubleshooting mode.

 

[Chaz]

Before I parked it last night I went to the store and it died on me 3x at stops. It didnt want to idle at all. Started it up this morn and it ran smooth while cold. Drove it up some hills to heat it up. Once it gets hot the probs start.

I switched the grn/wht injector plugs to drivers side. Map sensor vac hose looks good,,I had probs with that before its so close to the fuel line,,,,I snugged the tbi bolts and manifold bolts,,,that holley gasket is so thick is dosent get really tight but I dont want to crush it,,,ground wire is hooked up at the t-stat,,,

What it does (once warm) is at idle in drive (holding with footbrake or parking brake) it idles bout 550 rpm,,,then it starts missing,,,needle dips on the tach then it tries and corrects itself,,,runs up a little then back down to 550 rpm,,,if i start driving off the line it stumbles a little but if i hit the throttle harder it powers through,,,at higher rpms its smooth,,,,

I also replaced the fuel filter and tem coolant sensor today,,,no change so far

 

[Chaz]

I didnt set the idle or make any adjustments to the tbi when it was new,,,just bolted it on,,,,it has been running good for the past 4-5 months,,,,,the mechanic said when i was workin on the pwr window i prob left the key on to run the pwr window,,,he said it prob sent spark through the rotor cuz the rotor was burnt out,,,he said he tested the rotor and no charge went through it (it was new I put it on when i replaced manifold and tbi),,,,I know sounds like bs to me cuz i never heard anything like it before,,,

 

[Chaz]

Another thing,,,,the motor has always had a spark knock problem,,,it only spark knocks at a low rpm when its under a load,,,climbing a hill under heavy throttle,,,its short and goes away but its there,,,,I checked the timing,,,it was advanced bout 10 and I reset it to bout 1 deg btdc,,,,dont know if its related to current problem but Im thinking it shouldnt spark knock at all,,,,I hammer my 95 burban and it never spark knocks,,,

 

[Jims86]

Ok, next thing to check is the EGr vac control solenoid. if you have an extra piece of vacuum line that you dont mind sucking on, go out and plug that line into the EGR solenoid port that runs to the throttle body, and just disconnect the EGR side....if you are able to suck air through it, the solenoid is done, you need a new one.
The ignition might send a spark through when the key is turned on, then off again while the engine is off, but will not constantly throw spark unless the distributor is turning.
While we are at it....Do you still have your stock coil?More than. a few of us have been left walking due to aftermarket coils....our motto around here is, A/C Delco, or stay home....LOL

 

[HotRodPC]

At what temp does do you consider warmed up when it starts running bad? Coil is certianly worth a looking at if not an AC/Delco.

Another thing to consider, if it's running good cold or cool, and it waits till it's getting normal operating temperature, then that's a clue it can be and likely is something to do with an event that does not happen UNTIL the ECM goes into closed loop operation which is usually in the 185 to 190 area. Or, something that is connected to a TVS (Temperature Vacuum Switch).

 

[Jims86]

At what temp does do you consider warmed up when it starts running bad? Coil is certianly worth a looking at if not an AC/Delco.

Another thing to consider, if it's running good cold or cool, and it waits till it's getting normal operating temperature, then that's a clue it can be and likely is something to do with an event that does not happen UNTIL the ECM goes into closed loop operation which is usually in the 185 to 190 area. Or, something that is connected to a TVS (Temperature Vacuum Switch).

Probably when it goes to closed loop....thats generally when everything takes a nosedive when theres a problem.
No TVS to worry about.

 

[Chaz]

Ok I was able to suck air through both ends of what i think is the vacum control solenoid,,,,theres one hose goin from the egr valve (the diaphram thing bolted to the intake manifold),,,,to a black box mounted nxt to the map sensor,,,,then theres another hose going out of it to the throttle body,,,,i guess ill go get another one of those and also get a stock coil,,,,i thought bout the coil already I heard people had problems with the msd one,,,,

 

[Jims86]

Ok I was able to suck air through both ends of what i think is the vacum control solenoid,,,,theres one hose goin from the egr valve (the diaphram thing bolted to the intake manifold),,,,to a black box mounted nxt to the map sensor,,,,then theres another hose going out of it to the throttle body,,,,i guess ill go get another one of those and also get a stock coil,,,,i thought bout the coil already I heard people had problems with the msd one,,,,

Ok, go ahead and run the truck with the egr valve hose unplugged, and stick a pencil or screw in it to plug it off...see if there is any improvement.

 

[Chaz]

I ran it with the hose unplugged,,,,plugged the hose and it ran but it was worse,,,it was doin the same thing (idle ok then missing then idle ok then missing) but overall it was worse,,,bad throttle response,,,

I ordered the egr vac solenoid,,,prob gonna come in tomorrow or monday,,,it cost 80 bucks,,,and I got a stock coil,,,,I wouldnt be surprised if the whole problem was the coil,,,,

 

[Jims86]

I ran it with the hose unplugged,,,,plugged the hose and it ran but it was worse,,,it was doin the same thing (idle ok then missing then idle ok then missing) but overall it was worse,,,bad throttle response,,,

I ordered the egr vac solenoid,,,prob gonna come in tomorrow or monday,,,it cost 80 bucks,,,and I got a stock coil,,,,I wouldnt be surprised if the whole problem was the coil,,,,

It may be Ignition. So next, you need to pop your distributor cap off, and check it for side to side play(looking for worn out barings) or wobble, and look at the pickup coil below the rotor, make sure its not cracked and/or broken.

 

[Chaz]

Well heres the deal,,,,,I replaced the egr solenoid and put a stock coil on it,,,,right now its runnin like a clock,,,idles perfect,,,,I took it up and down hills,,,got on it hard,,,and I cant get it to spark knock anymore,,,,,,

So I cant say for sure if it was the coil or the egr solenoid but im betting that pos msd coil was was the cause of the engine running like s***,,,,,MORAL,,,,,msd coil BAD JUJU for a tbi motor,,,,,

Question,,,,would a bad egr solenoid cause the motor to spark knock because I was told the exhaust gas is circ'd into the intake charge to cool the intake charge to prevent spark knock???

Thanks for ur help Jim I hope it keeps running good cuz so I can work on other fun stuff like front brakes,,,,lol

 

[89Suburban]

Glad to hear it's straightened out mang.

 

[Jims86]

Well heres the deal,,,,,I replaced the egr solenoid and put a stock coil on it,,,,right now its runnin like a clock,,,idles perfect,,,,I took it up and down hills,,,got on it hard,,,and I cant get it to spark knock anymore,,,,,,

So I cant say for sure if it was the coil or the egr solenoid but im betting that pos msd coil was was the cause of the engine running like s***,,,,,MORAL,,,,,msd coil BAD JUJU for a tbi motor,,,,,

Question,,,,would a bad egr solenoid cause the motor to spark knock because I was told the exhaust gas is circ'd into the intake charge to cool the intake charge to prevent spark knock???

Thanks for ur help Jim I hope it keeps running good cuz so I can work on other fun stuff like front brakes,,,,lol

i would say at this point, it may have been a combo of both, but more towards the coil.
A spark knock is detonation. Either from a lean condition caused by a contaminated o2 sensor, Vacuum leak, or timing advanced too far, or too high compression, or wrong grade/Bad fuel.
Its also possible that you have carbon build up in the combustion chambers, slightly upping compression, carbon also glows red hot too, so that could cause the mixture to fire prematurely too.
A good top end cleaner like Barrymans, or seafom may be what you need as well.

Has the knock persisted since you reset the timing to 1*?