1987 Suburban TBI stalling...

[Bob Gervais]

I have a pretty annoying stalling problem on my 1987 Burb, 350 TBI.

A while back, I swapped distributors, with what I thought was the correct one. It was not, and the truck ran miserably. I put the stock one back in, and ever since it's stalled when putting it into D, or any gear for that matter.

I've checked: TPS voltage, timing, pickup coil, temp switch, EGR, MAP and EST operation. Checked for vacuum leaks. All seem normal.

I've replaced: Ignition coil, wires/plugs/cap/rotor are new within a year. All currently test/show good.

I actually had to turn up the idle so it would stay running in Park. If I keep my foot on the accelerator it will stay running in gear, but if I take it off it will stall after about 20 seconds or so.

I've checked and re-checked all connections, in case I knocked one loose doing the distributor install. Everything seems normal.

There's also no check engine light, complicating diagnosis even further.

This is really driving me insane, anyone have any suggestions?

Thanks in advance!

[magnethead]

how does it stall? does it run rough for 1 or 2 seconds then lock up, , run rough for quite a while then lock up, does it lock up without warning, or what?

does it have any sputtering when you start it? sounds like you torque convertor might be grabbing at too low of an RPM, or your idle is too high. check motor oil level [and for metal bits and pieces if need be], and check tranny fluid level. Check that the carburetor is operating propery (might have knocked off a vacuum line) along with the choke, and that the fuel pump is working properly.

[ElGracho]

This sounds to me like your timing is off a ways. The lack of initial advance is what killed your idle speed and power. That caused you to have to turn up the idle (the IAC valve is probably running full open and can't get the speed up high enough). The lack of power idling is what's killing your truck when you put it in drive and it gets the resistance of the torque converter slipping.

Read the manual for setting ignition timing with TPI/ computer controlled distributor and reset that.

[Bob Gervais]

I'll answer both posts at once.

magnethead: It doesn't sputter at all, it just dies after about 15-20 seconds. Right before it dies, the idle gets progressively slower. I'll check the trans fluid, and condition tonight.

ElGracho, this sounds like exactly what the problem is. I forgot to mention also, that if I disconnect the wire for setting the timing, and run the truck, it won't stall at all. Of course, there's little timing advance when that's disconnected, so the truck has no power like that.

I set the timing when the distributor was put in, and rechecked it Saturday. Right on 0, where the underhood sticker says to put it. One thing I thought of though, is that I should reset the idle and check the timing again. Apparently, there's a procedure for setting the idle that involves jumping the ALDL, and removing the IAC connector. I wasn't aware of that, and just set it like you would set curb idle on a carbed truck.

Thanks for the answers! Hopefully I can get this squared away and move onto the next projects on the truck.

[Bob Gervais]

Update:

I reset the idle (or "minimum air" as it was called in the instructions), as best I could. When following the procedure, I could not get it down to 450 RPM with the ALDL grounded, and the IAC disconnected. I got it down to about 700, and the truck stalled.

I then reset the timing, right at 0 again, and the truck behaved the same way. I advanced it 4 degrees, and still the same.

I checked the operation of the ESC according to the Haynes manual. Checked the timing at 2k RPM, then jumped the ALDL and checked again. It did not move from the original spot with the ALDL jumped, which according to Haynes means the ESC is not working properly. Of course, it doesn't say what could be wrong or how to check it.

I went ahead from there, trying to work as logically as possible. I checked the timing at idle, with everything connected, and it's about 8 BTDC. I operated the throttle by hand while watching the timing mark, and it actually retarded instead of advancing. I'm thinking this isn't normal. I checked all connections of the ESC system (knock sensor, ESC module) and all seems fine.

I also checked the fuel pressure, and it's right at 12.5 PSI.

I suppose from here I should install a new ESC module, and see what happens. I may just get one from a junkyard to see if it makes a difference.

By any chance, does anyone know if the ESC can be bypassed and still allow timing advance? And/or, does anyone know what the correct voltages should be at the ESC module connector harness?

TIA for any help!

[ureckme]

Im a new guy to. Just for kicks check timing see if it runs better with more advance. The closer to "0" does it run, not so good. Maybe Dist. is one tooth off?. Maybe Im way off. Matt

[Bob Gervais]

I've already tried advancing it 4 degrees, and it didn't make a difference.

The dist. being a tooth off is a possibility though. Would I still be able to set the timing properly with the dist. a tooth off?

[Jason Spears]

Are you sure you installed the distributor correctly? Did you make sure that you were on tdc on #1. I know I put a dist. in before 180 degrees off. You can get the marks to line up if you're one tooth off but the engine will not be timed. I would really recheck the distributor installation before I drive myself crazy with sensors and stuff.

A few other hints:

Make sure you erase the ecm's memory by disconnecting the battery for a few minutes after you reset the timing to 0 or the ecm will not start to control the timing.

When you are setting the minimum idle speed make sure you give the iac a enough time to seat itself. You might want to take it out to make sure it is not hanging up on anything. When the iac is seated in the bore make sure you unground the aldl terminal. Also make sure the engine is up to operating temperature. Try to set the engine speed to 500-550 with the trans in drive. (Get a helper!)

I'm not sure about that check of esc operation. It is nothing like the procedure in the GM service manual.

I hope this info helps. I know how frustrating these problems can be. Don't give up because it is usually one small mistake causing these problems.

Jason

[Bob Gervais]

This is exactly what I needed to hear Jason. I know it was on #1 TDC, but the possibility of being a tooth off is sounding like what's going on. The lack of a check engine light, or any codes, makes me think it's not a sensor, or anything like that, or even a wire that's chafed or unplugged.

Tomorrow's mission will be to check the dist. installation and re time.

Thanks very much for the input Jason!

[ureckme]

Hay what about me! I didnt get
73 Chevy SWB
406 SB Sportsman ll Heads 2.05 1.65 Angled Plugs 64cc
Holley 750 DP DF
TH350
2500 Stall
373 Posi
That even got more to list, By sticken my dist."in wrong". lol.

[Bob Gervais]

Sorry, didn't mean to leave you out!

Suppose I should have said thanks to all for the help.

[Ecnerwal]

This sounds veeery familar, though mine just developed over time. Also a TBI 350 from 87. Anyway, the solution was twofold, and may or may not apply to your problem. One was a new IAC valve, despite the computer not showing a code for it. The other was a new distributor shaft, and sensor bit on top. The new shaft has some extra grooves (sort of a screw-thread arrangement) to help keep oil from migrating up the shaft. The old shaft had worn until oil was creeping up it, and had soaked the sensor, resulting in weak and/or missed spark. The problem description was very much like what you stated - wanted to turn the idle up, or keep foot on gas, or it stalled constantly.

[Bob Gervais]

Success, sort of!

The distributor was one tooth off, and I corrected that yesterday. I then reset the "minimum air" by grounding the ALDL, turning the key to run, unplugging the IAC, then turning the key to off, ungrounding the ALDL, and setting the idle using the throttle plate screw.

It stays running in gear now, however the idle is about 850 RPM in D, around 1100 in P. It's always been this way since I got it three years ago, and I've tried alot of stuff. The IAC is fairly new, about a year or so old.

Ecnerwal, I don't see any oil under the cap, however the distributor shaft does move up about 3/16 of an inch if I pull up on it. I know they have some play, but this seems excessive.

I may still have more work to do, specifically figuring out why it needs to idle so high, but at least it's back to where it was before.

Again, a million thanks to those that offered advice. I probably would have been chasing this for a lot longer if it wasn't for the fine people on this site!

[Jason Spears]

Have you tried a new tbi to manifold gasket? This almost always seems to be the cause of a high idle problem in these vehicles. I've seen a lot of people (including myself) waste money on replacing the IAC and not have it solve the problem.

Other areas to check:

PCV
Brake booster and line to brake booster
play in tbi butterfly shaft
Vacuum line to tranny
All the other vacuum lines to the MAP, EGR and EGR soleniod, air pump solenoid etc.

Hope you find your last remaining problem. This one is easy compared to the distributor problem. Good luck.

[Bob Gervais]

I'll most likely be changing the intake gaskets, TBI base gasket, vacuum lines, etc. The TBI shaft is OK, I swapped it out for another unit last year, that had less play in the shaft. Now that I know the distributor stuff is ironed out, I'm planning on taking the valve covers, intake, air cleaner, and all the smaller brackets into work to sandblast and paint, so I figure doing all the lines and gaskets at the same time will not be a major issue.

Though I can't seem to find a leak, the truck seems to run better if I disconnect and plug the vacuum line from the vacuum canister (that little ball looking thing under the master cylinder). I'm planning on hunting down a new one of those as well.

It's nice to have the truck back on the road again though! I've never seen four kids so happy to see a rusty truck.

[gchemist]

Here are some links for trouble shooting.
http://www.california.com/~eagle/howell.html
http://www.cfm-tech.com/GM_tbi_tuning_tips.htm