TBI Burb dying in gear, My Turn.

[roundedline]

Ok guys, help me out here..   Finally got a chance to start diagnosing this since I want to take it to the Maggie Valley show in May...
90 350 TBI burb.  Wouldn't stay running and dies when stopping.  It was throwing codes and I replaced the IAC and EGR, both bad.  Codes are gone.
Still dies in gear and will eventually die in idle.  Pulled the Booster line off and the dying in park became sparadic.  Replaced the booster.
Now it idles around 675rpm and dies when it goes into gear.  Scanning it with WinALDL and the sensor data and raw data look ok to me.  (it does have and exhaust leak)
Pull the IAC connector and it runs fine and doesn't stall or die in gear.  IAC is good, removed from R10 to test it.
TPS data looks good also.  

Anyone care to throw out something obvious that I am now overlooking since I been working on it too long?

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

Edited by: roundedline at: 3/31/07 2:22 pm

[Lt.Del]

Getting down to basics, the ECM controls the IAC to keep the correct rpms at idle.  With no load, the setting should be around 20, of 256.  As a load to the engine takes place such as power steering, alternator, AC, or whatever, the rpms would fall.  But, the ECM steps up the valve to keep a constant rpm.

If you unplug the IAC, the engine does fine.  Try turning on the AC or turning the steering all the way one way or the other, turn headlights on, perhaps all of these while idling and see if RPM’s go down. It should if IAC is not hooked up. With IAC hooked up, the rpms will remain constant, in theory.

If you know the IAC valve is fine, something is telling the ECM to bring the IAC to a lower setting, therefore the engine stalls.

Why would the ECM be trying to set the IAC too low?? Is there an RPM sensor or other means that is giving the ECM false info?? (does ECM read the coil or distributor to get rpms?) Or you have a load at idle (AC on, power steering pump under pressure etc) and the ECM is not setting the IAC to a higher number.  ECM may be at fault.  On my wife's cherokee, the crankshaft position sensor failed and caused the engine to shut off--starving of gas due to the ecm telling the gas to shut off and killing the ignition.

IAC setting is displayed thru serial data.  You can play with the engine load at idle (AC, alt) and see if IAC setting changes.

I have heard of too high rpms.  Cruse Control parts can fail and lodge in the throttle cable, dirty throttle body etc..

A way you can check the crankshaft position sensor is when it shuts off again, keep key on (don't turn key to off position).  Turn the key to start the ignition again.  If it doesnt fire, or show spark, the sensor tells the ecm to keep the ignition off.  If after turning the key all the way off and waiting about 15 seconds and trying to start the engine again--basically resetting the cps, and it starts, well the cps may be bad.  But this doesnt answer the fact that when the IAC is unplugged, engine runs fine.

You mentioned you have an exhaust leak...is that before the O2 sensor?  If so, that would be allowing fresh O2 into the reading of the sensor. That in turn would create a richer mixture because the O2 sensor thinks more gas is required to burn the hydrocarbons.  

SgtDel
aka "Andy"

www.delbridge.net

1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4

Edited by: SgtDel  at: 3/31/07 7:32 pm

[VileZambonie]

Well if it dies only when you put it in gear the most likely cause is a vacuum leak. What are your IAC counts at idle? Did you check the TBI base gasket? Is your TPS set at .55V ?  

[roundedline]

Sorry I had enough of it yesterday that I just dropped it, since it was blocking my garage and I didn't want it dead there.

TPS is showing .57V at idle and the IAC count is averaging about 68 (ranging 63-70) which means leak to me.  Base gasket looked fine.

It eventually dies in Park after if fight to keep it running and looses.  I have checked what I believe is everything for a vacuum leak, I must just be overlooking something....  Just looking for fresh ideas.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[DnStClr]

Mass Airflow Sensor? (Air intake tube) While it's running you can take a screwdriver and rap it with the handle to see if it affects the idle- might even stall it out. If it does, that's the culprit.

Don St.Clair
Culleoka Tn

[VileZambonie]

There is no MAF on his truck it has speed density. I would spray the base of the TBI with some carb clean and see what happens. If that checks out ok pop the oil cap off and see if the engine speed changes and your IAC counts change.  

[roundedline]

Guess I should have stated that I basically sprayed the whole top of the motor down with carb cleaner while it was running on Saturday, no change in idle, no noticable leaks, which is why I got frustrated....

I passed this by my buddy at dinner tonight and he said it could be the intake gasket, I will check the oil cap tomorrow.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[Blazin]

Just tossing this in but I have had better luck with starting fluid than carb clean on stuborn or hard to find vacume leaks.

[VileZambonie]

If you it checks out ok then install a fuel pressure gauge and check your fuel pressure.

[roundedline]

Well, it still dies after it warms up, but I can put it in gear and it won't die when stopping anymore.  But it will die when going in reverse from a stop.  Here is the IAC sensor data from the time I cranked it in gear to the time it died, I can give you the whole dump (and raw data) if you want...

SENSOR:IAC
64
64
64
64
59
51
46
43
42
41
38
36
34
32
31
31
29
28
28
28
28
26
26
25
24
24
24
24
24
24
24
26
26
26
26
25
25
25
24
24
24
24
24
24
24
24
25
25
25
25
25
24
23
23

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[VileZambonie]

It should be able to hold a strong idle around 30 counts. What is your MAP voltage before it stalls? Is it setting any DTC's? Does it only stall once you put it in gear? If so how does it idle before you put it in gear and what is your IAC counts after you let it run for at least 60 seconds? The higher the count the more air it is bypassing the throttle plate to allow more air (increasing engine speed) 0 would indicate IAC all the way home 140 or higher is wide open. This can help you identify what's happening. Once you put a load on the engine at idle speed if it just stalls I would check the MAP voltage.  

[roundedline]

This is the sensor data from the time it is cranked to dying in gear:
Time        IAC        Temp        MAP
0.4        64        150.2        29.9
1.6        64        150.2        32.5
2.8        64        150.2        31.4
4        64        150.2        31.8
5.1        59        150.2        31
6.3        51        150.2        31.8
7.5        46        150.2        32.5
8.7        43        149.4        33.2
9.9        42        149.4        32.5
11.1        41        149.4        32.5
12.3        38        149.4        34.3
13.5        36        149.4        33.2
14.6        34        149.4        35.1
15.8        32        149.4        32.9
17        31        149.4        34
18.2        31        149.4        34.7
19.4        29        149.4        34
20.6        28        149.4        35.4
21.8        28        148.7        34
23        28        148.7        35.1
24.1        28        148.7        32.1
25.3        26        148.7        36.6
26.6        26        148.7        34.3
27.7        25        148.7        35.1
28.9        24        148.7        34
30.1        24        148.7        35.1
31.3        24        148.7        34
32.5        24        148.7        34.7
33.6        24        148.7        33.2
34.9        24        148.7        34.7
36.1        24        148.7        34.3
37.2        26        148.7        35.8
38.4        26        148.7        33.6
39.6        26        148.7        35.1
40.8        26        148.7        33.6
42        25        148.7        34.7
43.2        25        148.7        35.1
44.4        25        148.7        34.7
45.6        24        148.7        34.3
46.7        24        148.7        34.7
47.9        24        148.7        34.3
49.1        24        148.7        34.3
50.3        24        148.7        35.1
51.5        24        148.7        33.6
52.7        24        147.9        34.3
53.9        24        147.9        33.6
55.1        25        148.7        35.1
56.2        25        147.9        33.2
57.4        25        147.9        34.3
58.6        25        147.9        35.1
59.8        25        147.9        33.2
61        24        147.9        33.2
62.2        23        147.9        33.2
62.9        23        147.9        33.2

RPM        TPS        O2
850        0.7        0.495
825        0.7        0.495
875        0.7        0.495
850        0.7        0.495
800        0.7        0.495
775        0.7        0.491
725        0.7        0.491
700        0.7        0.473
700        0.7        0.477
700        0.7        0.473
675        0.7        0.469
675        0.7        0.486
625        0.7        0.46
650        0.7        0.486
650        0.7        0.469
625        0.7        0.469
625        0.7        0.486
600        0.7        0.455
625        0.7        0.477
600        0.7        0.464
675        0.7        0.486
575        0.7        0.473
650        0.7        0.473
625        0.7        0.469
625        0.7        0.477
575        0.7        0.464
625        0.7        0.486
600        0.7        0.473
625        0.7        0.482
600        0.7        0.477
600        0.7        0.486
575        0.7        0.473
625        0.7        0.482
600        0.7        0.477
625        0.7        0.486
575        0.7        0.495
575        0.7        0.491
600        0.7        0.495
600        0.7        0.495
575        0.7        0.491
600        0.7        0.486
600        0.7        0.495
550        0.7        0.486
575        0.7        0.495
600        0.7        0.491
625        0.7        0.499
625        0.7        0.504
600        0.7        0.508
625        0.7        0.508
550        0.7        0.504
600        0.7        0.508
625        0.7        0.513
600        0.7        0.504
600        0.7        0.504

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[roundedline]

No DTC's.  It dies after about 60 sec in gear, and it will stall going into gear.  Before it dies in gear the rpm drops and then it fights to keep it stable then loses.

IAC is at 23 when it is slowly dying. (no load applied).

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[VileZambonie]

OK just check your fuel pressure - if ok

Reset the IAC - Key off for 10 sec start the engine for 5 sec, key off for 10 sec again. Then unplug the IAC and start the engine. - Has anyone messed with the idle stop screw? Set the TPS to .55V If it's still stalling pull off the TBI - it probably sucked in the gasket between the IAC passage and primary's.

[roundedline]

Sorry, just getting back on this.  It was pooring down rain, then wife had her pins removed and now it is freezing (40's in Alabama)

Today:
Fuel pressure before the filter is a consistent 13lbs.  Set the TPS to .55V instead of .57. and did a reset on IAC.  I haven't had a chance to drive it yet, but temperature has changed now from 70's on the second to 40's today.  I am trying to get it up to operating temps and see if it will die once warmed up.  Plan to stop is and start it back up...

Right now it is running fine as I type this.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project