idling issues

[SloGN]

ok guys


I have been chasing down this weird/rough idle issue and it seems to have a hesitation when stepping on the throttle from a idle stand point.

So today i pulled the cap and rotor off and checked them out. It has a blue streak units int here and the cap and rotor looked great. i then ohmed out my plug wires and they are in decent shape. The truck had the ur5's in it so i swapped the plugs out for some autolite 23's gapped @ 30 thousandths. The rough idle/miss is still there. I also puled the TB and upper plenum off and checked/replaced some vac lines and i installed new gaskets. I also checked my fuel pressure and i have it set @ 42 psi witht he vac line off.


Now getting back to the ignition side of the deal the truck has a Red msd coil on it. So i borrowed a stock 93 ty coil on it and it seem to help with the hesitation. the rough idle is still there. could the msd coil be going bad. also this problem seems to show itself after the truck has been driven for a bit and warmed up good.

I don't have any type of a scan tool to look at the truck so i'm kinda lost here.


thanks guy this is my first issue with the truck.

 

[gkrcr882]

Re: idling issues

Might also be from "tip-in sag", which is caused by the design of the stock throttle body. Sounds like what you're describing, a slight stumble from when the throttle is opened to when the engine revs up.

 

[Don W.]

Re: idling issues

Same here on tip-in. Always been there. I did have a bad MSD coil right out of the box. Current MSD works but I didn't see any difference. Stock coil sent to "crispie." If it's JUST the tip-in I wouldn't spend a whole lot of time on it since you'll never run there. It's just frustrating. How does it run otherwise? Coil and/or module in the dis could be the problem.

FYI, I just paid a shop to put mine on a scope and tell me ya or nae on the entire ign systam. Turs out my dist was, in fact, bad. Changing the dist. made a noticable difference. Except at tip-in. :rotf:

 

[gkrcr882]

Re: idling issues

Flow boosters are supposed to help with the tip-in, but I dont know if they'll fit with our IC system.

 

[WyoSyclone]

Re: idling issues

Hate to be odd man out here.... but mine's smooth as butta' from an idle.... I do contribute it to being able to tune with Code59

...if you have a rough idle/miss you should probably go ahead and replace the ignition module just to be safe - I had one go bad on me in the middle of a run over the weekend and the Sy starting acting exactly like what you're describing... wasn't a total failure that left me stranded - I replaced it and everything went back to butta'

...might want to do a compression check too, to make sure you don't have one cylinder going down.

 

[SloGN]

Re: idling issues

Hate to be odd man out here.... but mine's smooth as butta' from an idle.... I do contribute it to being able to tune with Code59

...if you have a rough idle/miss you should probably go ahead and replace the ignition module just to be safe - I had one go bad on me in the middle of a run over the weekend and the Sy starting acting exactly like what you're describing... wasn't a total failure that left me stranded - I replaced it and everything went back to butta'

...might want to do a compression check too, to make sure you don't have one cylinder going down.

Ok I have replaced the ign module. The problem is still there. But i decided to recheck the timing and i had set the timing all wrong since there is to marks in the balancer. so i had my buddy recheck it and set it. Ok that helped it out a bunch.

well it's still running rough at an idle. so i was checking the vac lines again and when i pulled the vac tee off the back of the upper manifold. i noticed that it one about shut-off and two puking black smoke really bad so i assume not only did that line go to the fuel reg it also goes to the map sensor. so i plugged it back up and now the truck is running better?

So whatr could have i done by simply unplugging that vac line and plugging it back up make it run better? there was no leaks there. Did by flooding the motor with the extra fuel do something to it I/e wash some carbon away? now this has me stumped.

 

[Don W.]

Re: idling issues

Just adding air by opening, unplugging, that line should increase idle speed. That line goes to the FPR and that MAP sensor. Check the where they connect at each. Also while you have it off plug the line at the FPR start it up and see what happens. Might be a bad FPR.

 

[SloGN]

Re: idling issues

Just adding air by opening, unplugging, that line should increase idle speed. That line goes to the FPR and that MAP sensor. Check the where they connect at each. Also while you have it off plug the line at the FPR start it up and see what happens. Might be a bad FPR.

ok guys

When i went this morning go to work i was gonna drive the sy but it didn't want to crank it done nothing but turn over. I heard the fuel pump run and shut-off like ti normally does. after about the third try it finally started. When it started up acted like it was gonna choke out but it caught it self and ran great. I have already tried a new ecm in this thing. I'm about to go nuts over it.


thanks again guys for putting up with my porblems and rants.

 

[WyoSyclone]

Re: idling issues

sounds like you've probably got a vacuum line problem.... I'd probably start by replacing all of them....NAPA has all the check valves, etc. that you'll need.

 

[NecroWolf]

Re: idling issues

if the line to you map sensor is plugged you'll be getting faulty readings to the computer and it'll do odd stuff. if you have a stock regulator swap it, the lines for it and your map. if crap got in the map sensor line, you can be sure it got in your map and you fpr. these trucks will nickle and dime you to death if you're not careful. you need to either get a data master setup or a data logging scan tool. i got my mac obd1/2 scan tool at a local pawn shop for 300 and they had a cheaper one ther for like 80 dollars.

 

[syclone0209]

Re: idling issues

sometimes ive had flow problems with the little rubber elbows on the fpr and the map after they get old. try replacing them or just pushing the vac lines on.

 

[SY-1193]

Re: idling issues

Ok The problem is still there. But i decided to recheck the timing and i had set the timing all wrong since there is to marks in the balancer. so i had my buddy recheck it and set it. Ok that helped it out a bunch.

DId you unplug the Tan wire in the ECU wiring in the passenger side footwell when you set the timing to 0 degrees? If you have trouble starting it may be because your timing is off. If the timing was set to 0 degrees with the tan wire plugged in it would retard timing more to start and you would be way off causing a hard start. Double check your timing...especially since you say you have two??? timing marks on your balancer...

Hope that helps.

 

[SloGN]

Re: idling issues

DId you unplug the Tan wire in the ECU wiring in the passenger side footwell when you set the timing to 0 degrees? If you have trouble starting it may be because your timing is off. If the timing was set to 0 degrees with the tan wire plugged in it would retard timing more to start and you would be way off causing a hard start. Double check your timing...especially since you say you have two??? timing marks on your balancer...

Hope that helps.

yes i did unhook the tan est bypass wire under the heater box. But i can't understand why it has two marks on the balancer. i'm really starting to wonder if this truck is as stock asi thought it was when i bought it. It's really starting to looks like it has issues after issues.

 

[SloGN]

Re: idling issues

UPDATE.

I finally got the o2 sensor out of the downpipe after fighting with it. The last owner told me he had installed a new o2 sensor in it when he tuned it up last and from what he told me that was about 3-4k ago. But i installed a new sensor a bosch one. The truck seems to idle somewhat smooth and the biggest part of the hesatation is gone. how is the TPS adjustments made on these trucks. The buicks are set to .42-.45 volts @ idle. the truck seems to not be adjustable.

 

[Tooky]

Re: idling issues

My stock balancer has more than 1 groove too. I used White-Out to paint a white stripe on the TDC mark.

Those O2s can be a real beast to get out of the stock DP, Don't I know it!

The TPS is not adjustable. You can use a scan tool to verify that it reads 0.0% TPS at idle though.

 

[FxsX24]

Re: idling issues

on the 4.3 tbi trucks (and most other SBCs) you use the second mark while turning the motor to the right


what is the first one there for?

 

[FxsX24]

Re: idling issues

ah that makes sence