ECU connundrum

[70chevrolet]

VEHICLE IS 90 CHEVY K1500
5.7.LITER
5- SPEED MANUAL.

I have an ECU connundrum..




My EGR system is totally inoperative. The ECU for whatever reason is not commanding the egr solenoid. Using the factory manual Ive diagnosed the problem as fIollows.

Connect test light between harness connector terminals. Ignition ON, engine OFF. Test light should light.

If test light OFF, connect test light between harness terminal "A" (pink/black) and ground.

If test light OFF, repair open circuit 439. If test light ON, repair open circuit 435. If not open, ECM faulty.

Circuit 435 is the gray wire between the EGR solenoid terminal B and connector A4 on the ECM.

Circuit 439 is the pink/black wire from the EGR solenoid terminal A through the ECM/IGN circuit powered by the ignition switch."

I have 12 volts at terminal A, and terminal B is not showing ground as it should with ignition on, engine off. Ive traced back the the terminal B to the ECU (circut 435/pin a4/gray wire) and determined that the wire is not broken or severed and that the ECU, which commands ground to activate the EGR solenoid is not working. Ive also back probed all 4 grounds at the ECU using the following diagram (system ground and sensor grounds located at pins a11, a12, d1, d2) confirming that the ECU does not have any bad grounds.



Ruling out a ground issue and by matter of deduction, I am assuming the ECU is bad. However in my days, i have just never seen an ECU act so quirky. To the untrained eye, the truck runs decent, it just does NOT have EGR. it pings like holy hell under load at low rpm and throws copious soft code 32's at speeds above 35 mph.
Any opinions if my issue is likely in the ECU or perhaps the eprom. I am not farmilar with how these things work and not sure if it is logical that perhaps the EGR function was somhow ommited from the eprom.. also, Can I swap an eprom from another truck? They are easy enough to come by in automatic flavor, but mine is a 5-speed, does that make a difference?

thanks in advance.
Ive posed this over a full size chevy also but feel like I may have more luck here.

questions, commentary, argument, opinion?

oh yeah, here is my ecu and eprom for whatever that is worth.

[EagleMark]

Nice diagnostic work!

There should be 2 main ground wires from ECM to engine, usually front of intake and rear intake or head. They have 2 wires each, check them for continuity to ECM and also good ground to engine.

But I don't think you'll find ground on pin B unless EGR is commanded on? Which it won't at idle or parked, only under driving conditions. Would have to find a way to check that ground circuit when EGR is enabled.

It is rare for something to go wrong with ECM at this age, they went out usually when new and had a cold solder or? Chips never go bad and yes the BCC code does make a difference.

Your symptoms do sound like EGR not funtioning but ECM programming takes away fuel and adds spark during EGR operation, so yup, pinging is common.

[70chevrolet]

Nice diagnostic work!

There should be 2 main ground wires from ECM to engine, usually front of intake and rear intake or head. They have 2 wires each, check them for continuity to ECM and also good ground to engine.

But I don't think you'll find ground on pin B unless EGR is commanded on? Which it won't at idle or parked, only under driving conditions. Would have to find a way to check that ground circuit when EGR is enabled.

It is rare for something to go wrong with ECM at this age, they went out usually when new and had a cold solder or? Chips never go bad and yes the BCC code does make a difference.

Your symptoms do sound like EGR not funtioning but ECM programming takes away fuel and adds spark during EGR operation, so yup, pinging is common.

your right. I hooked up meter to egr solenoid and drove around watching for voltage. I do have EGR function it just pings like crazy and throws codes everyday.. thanks for jumping in anyway. I need to take more time and reflect upon this.

[EagleMark]

What codes?

What is fuel pressure? When it is low you will be lean and cause PING! Along with other lean codes...

[70chevrolet]

What codes?

What is fuel pressure? When it is low you will be lean and cause PING! Along with other lean codes...

Code 32.. Every day. And pinging under load below 1200 rpm.
Fuel pressure 14psi. I've been through the fuel system.
Only mods are. Edelbrock intake (the tbi one) and true dual exhaust.
i am wondering if the reduced back pressure is causing this. The plugs are reading a gorgeous chocolate brown color so the 02 sensor is working.

[EagleMark]

Yes, reduced back pressure will cause this. There's also a couple differant EGR valves that look identical that will cause the error 32. Look into this thread:
http://www.gearhead-efi.com/Fuel-Inj...BI-EGR-code-32

I also added the parameters to $42 XDF so when the EGR test is run, it can be changed to pass because of dual exhaust.

[70chevrolet]

Yes, reduced back pressure will cause this. There's also a couple differant EGR valves that look identical that will cause the error 32. Look into this thread:
http://www.gearhead-efi.com/Fuel-Inj...BI-EGR-code-32

I also added the parameters to $42 XDF so when the EGR test is run, it can be changed to pass because of dual exhaust.

Pardon my ignorance but what is $42 XDF? I've tried a few different EGR valves, the one in there now is ac delco with part number that was dealer supplied. Do you think if I put a factory y-pipe back on the truck then I would be able to get by without a cat or is the cat needed for additional back pressure? I only ask because a cat adds $200 to the price of a new exhaust system. Thanks again for your help with this.

[ony]

if this happen all at once I would try some better fuel, the egr wont work if it don't get the right readings for hydrocarbons.make sure inical timming is 0 degrezz. I have a v6 and it got carboned up bad and I couldn't run a 195 thermostat with out pinging ,after running some chevron cleaner though it I lowered the timming table above 75kpa on the map 2 degrezz helped a lot kind of waiting on out side temp to go up to 90 - 100 before if I really no if it fixed it. it was the same way but even at hyway speed it would knock bad while data loging at low rpm I could here it spark knock.

[70chevrolet]

if this happen all at once I would try some better fuel, the egr wont work if it don't get the right readings for hydrocarbons.make sure inical timming is 0 degrezz. I have a v6 and it got carboned up bad and I couldn't run a 195 thermostat with out pinging ,after running some chevron cleaner though it I lowered the timming table above 75kpa on the map 2 degrezz helped a lot kind of waiting on out side temp to go up to 90 - 100 before if I really no if it fixed it. it was the same way but even at hyway speed it would knock bad while data loging at low rpm I could here it spark knock.

Not sure what you mean by happen all at once. I've been chasing the EGR code for months. The pistons could have a carbon buildup, however when I pull the EGR plunger at idle, the engine coughs. Indicating that the EGR passages are clear. My timing is dead on at 0 degrees. I will try some high octane just to see what it does. That's a good idea. I'm prob gonna put the exhaust back stock or at least put back the factory y-pipe.

[jim_in_dorris]

I might be wrong here, but it does sound like your egr works, are you sure the electric vacuum switch that the ecm uses to control the egr is working properly? The second thing to look at is the thread that mark referenced. There are 2 types of EGR, a negative pressure and a positive pressure EGR. Almost all TBI trucks IIRC use a negative pressure EGR valve, a positive pressure EGR might work at idle, but not under load.

[EagleMark]

Pardon my ignorance but what is $42 XDF? I've tried a few different EGR valves, the one in there now is ac delco with part number that was dealer supplied. Do you think if I put a factory y-pipe back on the truck then I would be able to get by without a cat or is the cat needed for additional back pressure? I only ask because a cat adds $200 to the price of a new exhaust system. Thanks again for your help with this.

$42 XDF is the file you need to adjust the chip... this is a tuning site you know.

IF EGR is working, then your pinging is from another issue. Check fuel pressure!

The code 32 can happen when changing to dual exhaust as Jim has mentioned and the other thread. You'd be cheaper to buy a chip with the error 32 tests fixed so they can pass. You'd also get some power modifications like fixing what GM had to do rather then what they want to do. All that exhaust work sounds expensive as well as may not fix the issue?

[ony]

I have seen the blead off on the electric egr selonoid hooked up wrong so that when it opened it took a long time to close, I would have eagle mark burn you a chip . I have one v6 bin that throughs the egr code and it just not a good bin lots of weird % correction and bpw than most bins. some thing else is I had a coil to cap spark wire that was reversed making it jump spark in the cap, one end of the wire was to short buy 1/2-5/8 of an inch at low lugging rpms bad pinging.

[70chevrolet]

I have seen the blead off on the electric egr selonoid hooked up wrong so that when it opened it took a long time to close, I would have eagle mark burn you a chip . I have one v6 bin that throughs the egr code and it just not a good bin lots of weird % correction and bpw than most bins. some thing else is I had a coil to cap spark wire that was reversed making it jump spark in the cap, one end of the wire was to short buy 1/2-5/8 of an inch at low lugging rpms bad pinging.

Im on my 2nd New AC Delco EGR, new solenoid, new O2. New TPS. Thanks for the suggestion of the spark wires. I haven't double checked them yet and I will go through the wires for sure.
To me, at this point, I feel as is a chip is a bandaid. I'm not saying I won't go that route...eventually. But the chase is on. I'm gonna get this sucker in the can. I just dropped $325 at summit racing on new factory y-pipe and converter. Im gonna go back to factory restrictive exhaust from my true dual setup and see if that fixes the problem. I just ordered all the stuff today. I will post back once it is all installed.

[70chevrolet]

[EagleMark]

Nice truck!

Chip changes are not a bandaid. If done properly they are the solution to many issues. Now some companies are known to just disable EGR or even just turn off the CEL for that error. What I am suggesting is to change the EGR error 32 test so it passes with new exhaust flow.

Before you waste money on something that may not work? Stuff a towel in one side of exhaust, clear codes, go for a ride and see if error 32 comes back?