'87 R10 suburban 350 V8 TBI stalls at lights - suggestions?

[skizzik]

Hello Chevy experts!

My 1987 R10 Suburban 350 V8 TBI (K family) stalls at lights but will recover if I shift it into neutral fast enough while I hear it about to die. It also commonly happens when I'm pulling into or out of a parking spot. (Does this mean the official symptom is 'stalls when RPMs drop too low?')

I'm not a car expert, so I've done some googling and here's what I've done so far and here's what I know:

- first I replaced the fuel filter and air filter
- then I cleaned out the throttle body and IAC sensor with throttle body cleaner. Neither one seemed very dirty
- while doing that I watched the injectors spray and they appeared to be atomizing the fuel properly
- checked for vacuum leaks by spraying throttle body fluid on my hoses and at the base of the throttle body and did not hear any hissing noises. The previous owner removed the charcoal evap canister so that hose has a bolt tightly screwed into the end of it. Sprayed that too and didn't hear any hissing.
- replaced my spark plugs
- cleaned out my PCV valve. It sounds like it rattles properly when I shake it.
- fuel pump completely died last week. I replaced it, hoping it would solve my stalling problem but it didn't.
- engine light is not on. Sometimes it comes on if the truck is about to die but always goes away after I restart the engine or if the engine recovers. I haven't checked for error codes because I haven't found anyone that has the older type code reader.
- idle is already pretty high. Mechanic told me he was afraid to turn it up any higher.

Anybody know what I should do next? What can I do myself and what do I need a mechanic to do? Besides this stalling problem, this truck still drives great.


Thanks,
Mike

[nlped]

First, check the ECU for a code. You can just use a paperclip to jump the computer, then just count the flashes of the "check engine" light.

Put a paperclip in the AB terminals of the ALDL connector under the dash. It is the 2 in the top righthand position. turn the switch on and count the flashes. the first 3 will be 1 - 2 flash for 12. This just verify's that it working. Then start counting the flashes. It will do the same pair 3 times, then move to the next until it comes back around to 12.

[nlped]

The ECM incorporates a diagnostic program which, when activated, will flash codes stored in the trouble code memory through the "CHECK ENGINE" lamp. A diagnostic connector, located under the instrument panel, is used to activate the self-diagnosis system. The connector,allows access to system circuits and contains a test terminal which, when grounded with the ignition on and engine stopped, causes stored trouble codes to be flashed on the "CHECK ENGINE" lamp.

When the diagnostic terminal is grounded (jumper terminal "A" to "B") with the ignition on and engine stopped, codes are displayed in numerical order, always starting with Code 12 which indicates that the self-diagnosis system is operating properly. Trouble codes, are displayed in the following manner: Code 12 is displayed by one flash, a short pause, then two flashes and a longer pause. Code 12 will be displayed 3 times in this manner, then any additional codes stored will be displayed 3 times each in a similar manner until all codes have been displayed. Once all codes have been displayed. The process will be repeated as long as the test terminal remains grounded. DO NOT ground the diagnostic terminal until the ignition is "ON" and engine is "OFF" (not running). After trouble codes have been noted, the ground wire should be removed from the test lead and the engine should be started. When the engine is started and there are no other codes except Code 12, the "CHECK ENGINE" light should go out after approximately 5.0 seconds, indicating that the ECM has not detected a malfunction. However, if the ECM detects a current malfunction, the "CHECK ENGINE" lamp will remain illuminated while the engine is running. A trouble code indicates a possible system malfunction. If a trouble code can be obtained, even if the "CHECK ENGINE" lamp is "OFF" when the engine is running, a "SYSTEM PERFORMANCE CHECK" should be performed and the indicated circuit should be inspected.

Use the appropriate diagnostic charts if trouble codes can be obtained with the "CHECK ENGINE" lamp "OFF." A System Performance Check and a thorough physical inspection of the circuit involved should be carried out if any of these codes are evident. Repair as necessary.

Removing battery voltage to ECM terminal "R" for a period of 10 seconds will clear all stored trouble codes. This usually can be accomplished by removing the ECM fuse, if equipped, from the fuse block. In some cases it may be easier to disconnect the negative battery terminal. However, doing so will result in deprogrammed ETR radios, electronic clocks and Trip Computers.

[skizzik]

hey Thanks nlped. I had no idea I could get trouble codes that way. And thanks for the diagram too - very helpful. I'm definitely going to try reading codes this weekend and I'll post anything I find.

How's your '88 suburban running?

[nlped]

Not a problem!

My '88 is in pieces trying to sort out the suspension. It needs a new transmission, and the motor smokes like a tar kettle... so I think I will be putting a 6.0l & a 4L80e swap in it in the near future. But, I want to put the same swap into my '76 Blazer first, but it runs good. I may do the new model swap into the Blazer first and use the running gear out of it in the Burb first, then do the new model swap later on? We'll see.

[skizzik]

OK I checked for codes by grounding A&B with a paper clip with the ignition on but engine off and the 'Check Engine' light did not come on at all. Did not see any flashing whatsoever. I hear a single click noise when I ground. That's it. Does that mean I need a new ECM? Any idea how to troubleshoot this?

[nlped]

Sounds to me like it just didn't make a good connection. If it is working properly, it will give you the 12 code, no matter what. That is weird though...and no, it wouldn't run without it, I don't believe.

Ed

[russgt]

What rpm is the idle currently at? Do you have a 700r4 trans? Not sure if I have the right answers, but i am interested in helping

[skizzik]

Hmmm... I've tried multiple times and can't get any flashing whatsoever. Just a single clicking noise when I ground and I'm guessing that click means a successful ground. I don't think there's any way I'm doing it wrong. I'm guessing my diagnostics system isn't working correctly. Darn.

Pic1: picture of A&B jumped
Pic2: ignition on but engine off. Notice radio is on but no check engine light.

I'm trying to think what else I can do. I'm thinking about replacing the O2 sensor since it's cheap and I know that could alter the fuel/air mixture, but I don't know where it is. My Haynes manual described where it is but I can't seem to find it. Can you point me to it?

[skizzik]

Russgt,

The RPMs don't display on the dash so I have no idea. I'm kinda a car newbie. How can I find out what my RPM is at idle? Dunno the trans type either. It's been replaced a couple times and the mechanic didn't tell me what he was putting in...I assume the same model as the car came with? I know the VIN but don't know how to find out what trans type it came with.

[Stitch]

looks like you have A and M jumped together in the pic...make sure it's the one on the top right and the one right next to it on the left and not the one below it...

[skizzik]

Sorry for the bad picture (came off my cell phone). I definitely jumped A&B (the 2 in the top right) together and not A&M.

[Desert1957]

on my 87 this was the first symptom of low fuel pressure , changed the fuel pump (In the Tank) and its been good as new!

Desert

[skizzik]

Ya when I replaced my fuel pump last weekend I hoped it would fix the stalling problem but it didn't. I just tried getting codes from the ECM but I get no flashing engine light at all when I jump A&B. I just get a single clicking noise, which I'm guessing means I've grounded correctly. I'm guessing this means the diagnostics circuitry of the ECM isn't working properly.

Any idea what else I could try? I'm thinking about replacing the O2 sensor since it's cheap and I know it could affect my fuel/air mixture. What do you think? I've been trying to find it on my truck but I can't find it.

[Desert1957]

Originally Posted by skizzik

Ya when I replaced my fuel pump last weekend I hoped it would fix the stalling problem but it didn't. I just tried getting codes from the ECM but I get no flashing engine light at all when I jump A&B. I just get a single clicking noise, which I'm guessing means I've grounded correctly. I'm guessing this means the diagnostics circuitry of the ECM isn't working properly.

Any idea what else I could try? I'm thinking about replacing the O2 sensor since it's cheap and I know it could affect my fuel/air mixture. What do you think? I've been trying to find it on my truck but I can't find it.

Ok, let's start over,

Check engine light working? verify with key on run for a bulb check.
If working , try and get any codes if available.
If check engine light is on while its running , you will have to fix that problem FIRST.
Its stalling when? after it warms up?
If it runs ok in "Open Loop" while cold it probably something minor
If its running crappy all the time , It could be something more simple like the "EGR" valve is not seated or sticking open. This will cause stalling and surging.
With the air cleaner off , a working "TBI" will sound like a huge vacum leak as its controling the idle speed, Does your's sound like this?

check all these things and repost what you find....

Desert

PS: here is a link to make sure you are jumping the right terminals
http://www.troublecodes.net/GM/

[bigarmzz]

if it does it when it gets warm, it'd be a coolant temp sensor

[powerdriver 1958]

Just a Question , Does it slowly lose RPM at a stop light until it dies??
Or does it die suddenly??

[skizzik]

Check engine light is working (bulb ok). Light does not stay on while the car is running. Sometimes it'll come on right before the car's about to stall but then goes away if the engine recovers or won't be on when I restart the engine if it does stall.

Can't get any codes from the ECM at all; when I jump the diagnostic and ground terminals of the connector under the dash I hear a single click but check engine light doesn't flash at all (no code 12).

Stalling is more likely once the car is warm but it does do it while cold too. It doesn't slowly lose rpm and then die; it will run rough for about a second and then die and will recover if I manage to switch to neutral in time. Engine sounds great while driving and sounds great at idle. Then sometimes will suddenly die. I've gotten to the point where I just drive around switching to neutral as I'm pulling up to a stop (but who wants to drive like that - big pain).

I think the TBI sounds good when the air cleaner's off. You said it should sound like a giant vacuum leak, which makes me think hissing noise, but I wouldn't really say it hisses.

[joe231]

Switching into neutral keeps it from dying makes me wonder if the torque converter is un locking. I assume you have a TH700R4?
If so, try unplugging the trans connector (3 or 4 wire plug on the drivers side close to the shift lever) then drive it and see if the stall goes away.

[datguysaL]

yup could be torque converter not unlockn

[l-fire]

When you start the truck do you get the brake and seatbelt lights along with the startup chime?

[skizzik]

Oops. I just realized the engine light doesn't come on when I start the car. Thanks for pointing me in a helpful direction. The bulb probably died recently. I will replace it and try again to get codes.

[Smier]

Definately get the bulb fixed and recheck for codes, my 91 blazer was having similar problems and turned out to be the intake manifold gasket. Massive vacuum leak causing a high idle situation and stuttering and stalling when I'd pull up to a stop sign or red light. Even though my ECM and check engine light were functioning fine, it wouldn't store any codes. Finally figured it out because the gasket finally let go enough to start burning coolant... New intake manifold gasket and reset the timing an idle settings, an it runs like a new truck. I also second the coolant temperature sensor being a possibility.

[skizzik]

OK at the moment I'm tackling this from 2 fronts...

1) still trying to get codes by replacing the bulb for the 'Service Engine Soon light'. While trying to get the bulb out, the whole socket fell back and then dropped behind the dash and then rolled out by my feet. Right now I'm trying to figure out how to reconnect it and I'm hoping I won't have to take out the rest of the dash to do that. I don't even know what wire was connected to the socket or where that wire is.

2) trying to replace cheap parts. I went to AutoZone and talked to someone there and he looked under my hood. He was surprised that the engine sounded so good. Anyway, he showed me where the coolent temperature sensor was (since I didn't know), was unable to show me where the O2 sensor was, and recommended that I try swapping out the throttle position sensor. He said I could return it if it didn't fix the problem, as long as I return it clean and within a few days. I'm currently looking into what work is required to replace the TPS. Can I just use a torx to take the old one off and pop the new one on? Or do I have to take off the TB? Do you all think I'm wasting my time with the TPS and should try replacing the coolant temp sensor first?

Thanks.

[Smier]

I wouldn't replace anything until you get the check engine light working and pull any codes that might be stored... There are two many possibilities of what it could be, and I hate just throwing parts at it, hardly ever works and usually just costs you more $$$ and frustration in the long run.