wgirnius

Firstly, Glad to be here. My uncle had an 87 suburban 1500 4wd 350 5.7 Vin K that a local mechanic has totally hosed up. He offered the truck to me for cheap. I bought it, there are so so many things wrong.

My uncle is not mechanically inclined, I am somewhat knowledgeable, but my experience is mainly in jet skis and motorcycles... two strokes, things with carbs and injected VWs.

The TBI world is pretty new to me. I'm in Lawrence KS if anyone is local I'd love to pick your brain.

The long saga.... original problem (From my uncle)
Suburban dies when stopping or slowing down... started mild, got worse.
Local mechanic aka Mr Bad wrench finds supposed blown head gasket, offers to swap engine from a suburban in his "back lot"
Uncle pays 1000 for swap... problem still there.
Mr Bad wrench says must be computer... charged 200 for a junkyard computer swap.
Mr bad wrench says must be fuel pump, charged 300 for fuel pump.
Transmission starts slipping, still dying.. Mr Bad Wrench says tranny needs rebuilt... 1300.00 later tranny rebuilt.
Stalling is so bad uncle parks truck, buys a buick. Two years later, sells truck to me for a grand.

I've owned it two weeks. Managed to get it started, drove it 15 miles home, used about 3 gallons of gas to get it home.
Symptoms:
On the way home: won't idle, periods of no power and stalling even at highway speeds. Used the two foot method to keep it running at stop signs lights, etc. Pretty much had to floor it to keep it going 55, then it would recover and seem normal for a few miles. Off and on, all the way home.

Closer inspection reveals:
Motor mounts loose, 3 spark plugs finger tight, one spark plug in two threads. Scan tool shows lazy IAC, and lazy o2. ECM is dangling from mount interfering with Heater operation. SES light burned out.... hmm coincidence? Hard to start hot or cold. Idle adjustment plug removed on TBI body.

What I have done:
Installed new spark plugs.
Fuel Filter
Air Filter
Installed TBI rebuild kit (to make sure base gasket ok)
Installed new o2.
Installed new IAC.
Cleaned EGR
problem was slightly better, but still unpredictable. Still very hard to start, warm or cold. Idle bouncing between 350 and 900.
Checked timing, not too bad. Checked rotor.. OMG! distributor is rusted, some magnets are broken off, can't believe it ran at all.
Replaced distributor.
Replaced CAP
Replaced rotor
Replaced Wires.
Replaced Belts.
Replaced all console and instrument bulbs.
Re timed.

Extended driveway testing still throws a 44 after a few minutes in closed loop, now with good distributor runs worse. But does start a little easier.

I'm going to guess Mr Bad Wrench didn't replace the fuel pump, but the relay looks new. I could run a pressure test, but I'm going to drop the tank anyway.. if Mr Badwrench did, I "Must" inspect it after everything else I've found.

How am I doing? Any suggestions? I'm starting to loose my confidence.

Joelkatdaddy

Hey, im from Olathe. Did you unplug the est wire to set the timing?

wgirnius

Yup I did, I bought both service manuals, the Haynes and the Chilton, because they both are kinda lame.

The good news is everything I replaced was worn out, even though it wasn't the problem. I just got out from underneath. I'm trying to figure out how I'm supposed to get the skid plate for the gas tank off. The truck has the 40gal option with the skid plate.

Joelkatdaddy

Well let us know how tha goes. If you dont get it figured out i might be able to come take a look at it next weekend. Il be in lawrence sometime.
Joel

wgirnius

Okay... how am I supposed to get a wrench inside there to get the skidplate off. Looks like I have to remove the bumper?

Anyone have any tricks on this? Or is it generally just a pain no matter what you do?

RFmaster

Hey Joel

That's some laundry list of parts you have replaced so far ;(. Lets see if we can get that old 'burb back to running condition. And - do not loose confidence - there are millions of these TBI trucks still roaming roads just about everywhere.

1) Q - do you still get code 44??? Code 44 indicates that the O2 sensor is showing a persistently high exhaust oxygen content (lean), despite the efforts of the ECM to increase injector on-time (thus increasing fuel delivered). Do you have AIR system installed??? Check Pin C2 on your ECM interface connector (AIR solenoid control, brown wire) Get a DVM and measure voltage at that pin with respect to ground. It should be about 12.8+ with warm engine idling. ECM pulls this line down to about 0.7 V to activate AIR bypass solenoid, however if this line was pinched (shorted) to ground the AIR diverter solenoid is always ON injecting air into exhaust manifold causing a false lean condition. A quick test is to disconnect AIR diverter solenoid from ECM harness at the diverter. Also check for exhaust manifold leaks or vacuum leaks. An exhaust leak will screw up NBO every time.

2) A persistent lean condition can also be caused by a low fuel pressure - verify that the bozo bad wrench did replaced fuel pump, as claimed. You should be seeing steady 13+ PSI. Did you replace fuel filter???

3) Which engine and ECM type you have in your burb (1227747 and BCC code = ASDU??)

//RF

wgirnius

The last time I ran it it didn't throw the 44, but the time before that, it did.
At this point, I'm still just trying to get it to idle. I'm actually a little afraid to take on the road yet, it's very hard to start, you have to crack the pedal a little to start her.. Yeah, sounds like fuel pump to me too.
But, yesterday, I decided to adjust the idle with the screwed up plug removed and TBI mangled adjustment. I figure since I"m never going to know where it's supposed to be, if everything else is right, maybe it's this I need to put back. I increased it a little and it smoothed out.. but it's done this before, it's just mocking me at this point I didn't verify the RPM, I was just pretty happy to hear it idle. Time will tell what's up.

I'll check that air subsystem, thanks for the great tip! A lot of my idle testing was done with the air cleaner off, would that have any effect?

Yes, I did put a fuel filter in it already.


Where do I find that ECM information, is it stamped on the side? The scanner wasn't mine, it was a friends, I should have written that down.


Any tricks on the skid plate?

RFmaster

wgirnius

Minimum idle screw is used to set idle with EST in bypass mode - i.e . connector open. It should be very low around 450 to 500 RPM for a stock engine (timing should be around 0 deg) provided that you have no vacuum leaks and injectors are firing enough fuel. Low fuel pressure shows up as surging idle. IAC kicks in as a stall saver routine tries to keep idle RPM above minimum ~ 600 RPM for a warm engine.

Check fuel pressure to rule fuel delivery issues first.

There should be a paper label on the cover of the ECM - Service number.

//RF

wgirnius

Update: My uncle, who I bought it from, paid 300 for a fuel pump, which is why we didn't go that direction originally. We did a fuel pressure test, it eventually got up to 12psi, but it took 30 seconds of cranking. Fuel volume test confirmed it was the pump. Only made 3 oz after 15 seconds.

Removed the skid plate using a distributor wrench an extension and a break over bar, dropped tank, cleaned up the rust, painted and installed a new bosch fuel pump. The pump that was in there was an actual AC delco, and the hose looked original, but there was an old fuel sock in the bottom of the tank outside the baffle. I think they guy just ripped him off, or put in a used pump.

Starts immediately now, power is back, idles good. Small hesitation while first accelerating from a dead stop, but we'll work on that.

wgirnius

Okay, I'm stuck again. But significant progress has been made.

I'm now only fighting with the stalling at 1/8th throttle. If I just drive like I mean it, you can't even tell. It is no longer throwing any codes. New plugs wires, filter, distributor, IAC, TBI rebuild kit, new tires, fixed all the locks and power windows. No longer throwing any codes. Power seems normal except at 1/8th throttle. Set timing to 0, idle to 650 with the thingy (EST?) disconnected.

So here is what happens. Starts right up, every time, even after this happens. Doesn't matter if it's hot or cold.
Slowly depressing the accelerator it starts to just engage the converter and move the vehicle. Then it stumbles, acts like it's running on 5 cylinders, lots of engine vibration, the whole truck shudders. If you let off, sometimes it will idle down to normal, but it's like it has to clear itself out. If you punch it, it recovers, but since I bought it to put boats in the water, that isn't going to work.

When it dies, it starts up immediately and idles normal, no codes. This symptom is repeatable, every time, all the time. It's not something you necessarily would notice during normal driving, just when you are trying to go slow under load.

What do you all think?

RFmaster

wgirnius

It maybe a TPS giving a problem - Get A DVM and back probe Pin B - dark blue wire. At idle it should read 0.55 Vdc and as you move throttle the voltage should increase nice and smooth to 4.5 Vdc at WOT. Any jumps in voltage may cause ECM to alter fuel mixture.
The other possible culprit is a leaky EGR valve. Check EGR valve digraph with a hand pump.


//RF

wgirnius

Okay, we've made some progress. The TPS is smooth throughout it's range of motion. The EGR valve however, is another matter, it does some weird things. Disconnecting it's vacuum line makes the slow speed issue go away, my mechanic friend doesn't think the one that is on it is the right one. He says it responds to retract too fast, but closes too slow.

Anyone have any idea what EGR valve is supposed to be on this, he doesn't think it's the right one, he thinks the orifice is too big. It appears to be a factory one. But this truck had a motor swap by a moron. He is thinking that the ECU mapping might not match the egr valve on the engine.

RFmaster

EGR - is tricky one to troubleshoot since there are different versions used... Do you have EGCV solenoid inline between EGR and TB vacuum outlet?? It may defective or it has its bleed off port restricted.

//RF

wgirnius

Yes, mine has that solenoid. On the scantool at idle the map was reading only .72 - .80 manifold pressure, should be 1.0 or better. So here is the ultimate question.... is the Map sensor bad, tripping the egr too soon, or the solenoid leaking, or is the egr leaking or is it the wrong one. The EGR appears to hold a vacuum, it's just opening too far, to soon.

RFmaster

I am not sure what your scan tool is configured to report, but here is a basic skinny. MAP sensor, at idle, on stock engine which has about 18 in-Hg at idle should report about 1.1 to 1.8 Vdc which roughly corresponds to 20 to 16 in-Hg or about 30 to 40 kPa. ECM uses multiple inputs to determine when to activate EGR - this really determined by BCC (EPROM calibration). In some application EGR is disabled at idle, in some it is not. There are just too many variables, but generally you want that thing active above idle, while cruising. I hope this helps.

//RF

wgirnius

I don't know what measurement it's using either. It's an old Snap-on red brick ODBI scan tool, borrowed from a friend. Everytime I need it, I have to have him come over so I don't have it at my disposal all the time. The onboard menu's tell us what the reading is supposed to be, it says that map reading should be no less than 1.00 and it's sitting around .76. I'm guessing it's volts. We changed the vacuum line to the Map and got the same reading, so the line itself is good.

wgirnius

Okay, new request for help. I'm stuck, and I've noticed something new.

First of all, the snap on scan tool was used with a brand new AC Delco MAP sensor from the dealer. We are showing 27KPa at idle at .88v Still does the bogging with 1/8th throttle and dying. Watching the scan tool the 02 sensor pegs at 920 with the throttle in this position, the truck does it's thing and the IAC opens to 140 to try to compensate. Unplugging the EGR solenoid electrical connector makes it run great at this throttle position.

Further examination of the scan tool data, shows the prom ID as a 9931, according to my book, that's for a freaking 305.

For all I know, the engine mr badwrench put in is, a 305, I'm not sure. Here is what is on the engine.
V0826FBM
TS705455

HELP!

Thank you.

RFmaster

wgirnius

OK - lets break this down into manageable work areas:

1) According to one source engine code V0826FBM comes back to

V = Flint (Engine)
08 = August
26 = Day of the month
FBM = Engine Suffix Code

FBM was used on a 1987 350 CID truck V8. I have no idea what TS705455 comes back to - probably part of VIN.

2) EPROM ID 9931 means very little - take a look at the broadcast code printed on ECM label cover or on EPROM chip - it should a four letter combination -ASDU, ASDZ, ASAX, or similar. You should have ECM with service number 1227747. It is not unusual for Mr. bad wrench to swap ECM blindly without concern to calibration. BTW, ASDU calibration was used in CA suburbans (I pulled one out JY burban), and ASDZ was used with 305 truck.

3) 27KPa with 0.88 V at idle is very good. That engine probably idles at 500 RPM without you knowing. When O2 hits 920 mV means that for what ever reason ECM is dumping excess fuel (very rich ) at that throttle position. When EGR opens up it tends to lean out intake mixture by allowing some of the inert exhaust gases into intake manifold. It is possible that EGR in your engine is dumping too much exhaust charge into intake - leaning out mixture until O2 reports it and then ECM adds fuel, and keeps on adding fuel. Can you record both TPS and MAP values with EGR connected & disconnected?

//RF.

wgirnius

Okay, here are all the details:

The Vin: 1GNEV16KXHF002007
The Information on the Plastic Bracket that holds the ECM under the glovebox
16069931 ACSU
869931m628759

ECM Sticker (GM Re-manufactured)
Number 7-7747
DC Code 1105YG

Prom: ACSU 0024

Sticker on ECM Motherboard
07774700052980050 REMFG

EGR Disconnected, Idling Closed loop in Park
RPM 800
TPS .66v
IAC 40
MAP 31KPa 1.12v

EGR Disconnected, Idling Closed loop in Drive
RPM 650
TPS .66
IAC 30
MAP 36 KPa 1.4v

EGR Disconnected in Park at Stumbling point
RPM 1100
TPS .92
IAC 45
MAP 44KPa 1.84v

EGR On Park at Idle Closed loop
RPM 700
TPS .66
IAC 20
MAP 32KPa 1.2v

EGR in Drive at Idle Closed Loo
RPM 600
TPS .66
IAC 20
MAP 37KPa 1.46v

EGR in Drive, accelerated to Stumble Point
RPM 800
TPS .94
IAC 38
MAP 79KPa 3.64v

RFmaster

wgirnius

1)
EGR Disconnected in Park at Stumbling point
RPM 1100
TPS .92
IAC 45
MAP 44KPa 1.84v

EGR in Drive, accelerated to Stumble Point
RPM 800
TPS .94
IAC 38
MAP 79KPa 3.64v

MAP sensor is seeing a much lower vacuum when EGR is operating. Couple of reasons for that. Do you have MAP sensor vacuum line going to the back side of TB body to pick up vacuum???? MAP should the only line connected to that port - between fuel inlet and outlet. EGR and AIR diverter valves should be feed from the front vacuum tap. Another remote possibility is a leak in EGR circuit.

2) Your truck is running BCC ACSU, and your ECM (remfg) is 1227747. According to Diy-EFI ACSU calibration was used 1987-90 truck 5.7 V8 TBI “K” L05. Snap-on info is not correct.

//RF

wgirnius

Yes, we have a vacuum connection on the back of the TB that goes to the MAP sensor. We tried putting a new hose on their before we replaced the MAP.
On the front of the TB, we have three ports, the drivers side goes to the canister, the center goes to the PCV, the passenger's side goes to a special line that y's, one going to the egr solenoid, the other to the air pump system.

We did a physical test on the egr valve with a vacuum line and a brake bleed pump to test the response time on how much it took to retract it, and how fast it released. We then went to Napa and performed the same test on a new delphi unit. The results were identical, so we did not purchase a new egr valve.

We just came back from a test drive, it's slightly better with the new MAP in place. but it still does it. Normal city driving doesn't display the issue clearly, the best way to display the problem is when I try to backup into my driveway which is about 7deg grade, at those slow speeds, it bogs and dies every time. Power braking the vehicle in gear, will produce the same effect, which is how we attained the readings we provided.

We have absolutely no idea what is causing this, we think that the ecm or more specifically the programming on that prom is simply commanding egr on via the solenoid way too early.

If anyone would like to come by, and scratch their head and have some beer, we'd love to entertain them.

RFmaster

Your vacuum connections are right on the money. I wonder if you have a vacuum leak between intake and head right where EGR crossover passage. Or possibly mr. Bad wrench used a universal intake gasket without crossover restriction plate. When EGR opens up it just allows to suck in too much of exhaust into intake manifold.

//RF

wgirnius

Would I be able to verify this with a bore scope by any chance?

wgirnius

Quick question. I just remembered something that might be important. Apparently, I just remembered this, the FIRST thing Mr Badwrench charged my uncle for that was supposed to fix all this, was removing the cat.

The cat was removed by mr badwrench, the exhaust otherwise seems intact, cast iron manifold, single 02 on the drivers side, then they two go into one, and that shiny metal where the cat used to be.

Or, I'm thinking outloud here, could the run to the air system be leaking... or perhaps what it hooks to. Something to check bright and early tomorrow.

RFmaster

Yes, bore scope could be used to see if there is a restricter plate - all it is a thin shim of metal with small hole to keep amount of gas flow in check.

Otherwise I would start addressing EGR activation point through EPROM changes.
//RF

wgirnius

Well, I went to the junkyard to pick up a few things for the suburban, and snagged two more computers for 15 bucks a piece. One was coded the same, the other different.

I tried both, it's not the computer. Does anyone have a pic or a diagram of what the restrictor looks like?

wgirnius

It was the EGR valve itself. Even though it opens and closes, responds to a pulse, holds a vacuum, the spring must have been broken inside and rusted. Who would think a 20 year old spring would die before a 20 year old diaphram.

It runs like a top now, all issues addressed, except the comfort level stuff.

Now.. on the AC.

Thank you each and everyone for your assistance. I have learned a great deal from all this.

vette gator

Glad to hear that it's fixed. This has been a great thread to follow and learn things. It will be very satisfying to drive the Suburban past Mr. Badwrench's shop and listen to the sweet sound of a fine-running motor, no thanks to him.

RFmaster

I am glad that you got your problem solved. And actually I would like to thank you for posting what was the root of the problem - broken spring in the EGR valve! I have never seen a broken spring before - all failed EGR's that I have replaced were for leaky diaphragms - hence a better question for the future would be: "Can you see your EGR diaphragm moving back on forth when vacuum is applied and removed". Sorry, but AC systems are all Greek to me.

//RF

K5JMP

I have an '88 that drove me nuts for a bit...

wgirnius

Just for fun, we were so mad at the old egr valve we dissected it. The spring looked brand new, but obviously, the tensions on that spring, coupled with the age of the diaphragm apparently is enough after 21 years to cause this problem even though, in all appearances it looks ok. I sure learned this lesson.
Oh, and then we smashed the stuffings out of it right before we round filed it. Yes, Childish, but, very rewarding
Drove out of town today on dirt roads and got to throw her in 4wd. It's a happy truck. And, I have three computers to play with (All good), can you say it's time to do some tweakin
I think one of the computers was an AJAK not sure, but that's what I left in it because it compensated better even with the bad egr. It also appeared to run a little leaner, I'm hoping for more mileage. I'm going to take her to work with the AJAK computer and check the fuel mileage and then perform the same test on the stock one. Could be good information for everyone.

wgirnius

The first test has been done. AJAK ecm with my stock 350 tbi went on a 100 mile trip today with a full tank and two occupants, outside temp was 90deg, made 15.6 mpg running the stock tires. I'm really ecstatic about that.