'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

[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??

[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

[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.

[skizzik]

Replaced the coolant temperature sensor today, no change. Still stalling.

Spent some time trying to reconnect the socket for the Check Engine light by trying to reach it from under the dash but couldn't seem to get the socket back in. I just gotta turn the socket and it'll lock into place with the contacts touching the contacts behind it, right? Tried to take the rest of the dash off to get behind the speedometer but reached a roadblock there too. Don't wanna take too much apart since this is my DD.

Smier, I think you're right. I was so hopeful about the coolant temp sensor, but since that didn't work I'm officially hesitant to keep blindly replacing parts.

[skizzik]

Status update -

I fixed the SES light and pulled codes 24 (vehicle speed sensor), 33 (MAP sensor), and 44 (lean exhaust). These codes must have been stored in the ECM for a long time because my battery hadn't been disconnected in a long time. I noticed the Throttle Position Sensor and the end of the throttle shaft that it sits against were gunked up so I cleaned the area and put in a new TPS and then disconnected the battery for a few minutes to clear all codes and then went for a drive. It didn't stall while I drove but now it's running really rough at lights and the idle sounds really high when I switch to neutral or park. Pulled codes when I got home and picked up error 33 again (MAP sensor).

Thoughts?

Replace the MAP sensor? Is it possible the previous owner tried fixing the stalling-at-lights problem by turning the idle up too high and now all I need to do is turn the idle down? I should point out that all I did for the new TPS was stick it on. I was just reading online that many Throttle Position Sensors require initial adjustment - should I have done that?

[Desert1957]

Before you replace the "Map Sensor" I would make sure the vacum line going to it is in good shape. If it has a hole, or is disconnected the sensor will think the engine is wide open throttle and will go FULL RICH, poor idle , black smoke and other problems.

Remember "TBI" GM engines DO have a re-learn feature , everytime the Computer or Battery is disconnected , may take a few miles to re-learn all parameters.

Desert

[nlped]

I had pretty much the same issue with my old '87. It threw the MAP sensor code too, and like Desert said, I checked the vacuum line first & sure enough it had a small melted spot in it. I replaced the line, cleaned the vacuum source nipple (I love saying nipple ) out with some cleaner spray, and poof...Good as new. Give it a try.

I don't know about the TPS on these trucks, but I do know that you need to adjust them on some imports, and my mustangs. I'm sure someone can chime in on this though.

Good Luck,

Ed

[Smier]

Yes, thoroughly go over all vacuum lines for leaks. Another common symptom on these TBI motors with a vacuum leak is an unusually high idle. Another good source for info on TBI setups is thirdgen.org, it's a site dedicated to 1982 to 1992 camaros, but they used the same TBI setups on our trucks and there are a lot of guys on there that know there stuff!!! A simple google search will give you info on how to diagnose the codes. Remember, just because you have a map code doesn't mean the map sensor is bad... It could be or something else might be causing it to act up. But it will point you in a direction. Be patient, keep posting up what you find and guys will try and help you out. Take your time and inspect connectors and clean up things as you go, I actually was fighting several problems on mine at the same time which made diagnosing difficult at times. I'd fix a problem, and it'd run better, but not 100%.

[skizzik]

Latest update:

I've thoroughly checked for vacuum leaks - by spraying throttle body cleaner on all vacuum hoses and at the base of the throttle body and visually inspecting everything - and can't find any leaks.

I'm getting flash codes for the TPS and MAP sensor, even after replacing the TPS. I then decided to concentrate on the MAP error and assume the TPS error will go away when the MAP error does.

I noticed that the output of the throttle body (the part where the vacuum hose connects out to the MAP sensor) was clogged with gunk. I sprayed throttle body cleaner into it and tried cleaning it with q-tips and one of the cottony q-tip ends got stuck in the throttle body.

Is that worth worrying about? Is there a better way to clean that area? Once I'm sure that area is clean, my next step is going to be replacing the MAP sensor.

[Jonboy]

You will have to adjust the TPS voltage if you have replaced the sensor. IIRC, it should be .45V at idle (no pressure on the throttle) and ~5V at Wide open throttle (WOT). With a voltmeter connected, there thould be a sweep in the voltage readings from closed to WOT.

Looking at your other post, you will probably want to put in a speedo cable and see what that does. Driving with no VSS could have smoked the torque converter clutch, as well as given a lot of other false readings as well.

[skizzik]

I figured out my problem. Turns out I've got 2 issues, MAP error and VSS error. I'll talk about the MAP error here and close the thread, because I've gotten the MAP error to go away, and concentrate on the VSS error on my other threat.

The previous owner of my suburban disconnected the charcoal canister, so the tube to where the canister used to be is just sitting there. I just noticed that somebody (it must've been a mechanic, because it wasn't me) plugged the end of that cable with a bolt. I guess they thought it would cause a vacuum problem to have it not plugged? Anyway, when I took the bolt out, the MAP error went away.

Anyone have any idea why?

[skizzik]

OK I finally got this figured out... I think the plastic speedometer driven gear is stripped and not turning, so the speedo cable doesn't turn, so the speedometer doesn't work, so the VSS constantly tells the engine that I'm not moving.

I think all I've got to do is replace the speedo driven gear. The dealership doesn't even carry it anymore (at least the one I need, with 38 teeth), but I think I can get one online.

Thanks for everyone's help, I wouldn't have known how to pull codes without your help.

[skizzik]

this thread can be closed.

[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.