Engine hesitates and stumbles after installing new wiring harness

[BruceHislop]

Hi All

I thought I had the issue solved when I measured the voltage on the spark advance control wire going to the electronic distributor.  The Electronic spark control is disabled when starting the engine.  When the RPMS hit ~400 RPM, the ECM sends 5V to the distributor module to enable ESC. When I started the engine it would go to 5v then drop to zero.  However when I plugged the connector back together and probed the wire, the voltage stayed at 5V.

I have now re-installed the old HEI mechanical distributor with the 12 to 5 V level buffer, as it was before and working fine.  The engine still stumbles and hesitates.

I monitored the power to the ECM with a scope and it is clean and stable.  I then ran a separate power wire direct to from the battery to the HEI for clean power, still the same.

It seems to be more an electrical (spark) issue as it occurs and clears abruptly.

The fuel pressure gauge is steady at 15psi.

JimH, the engine temperature as monitored by the EBL is 80 degrees C, so coolant is reaching the sensor.

I loosened the gas cap in case the Evap system was faulty and not allowing air into the fuel tank causing the fuel pump act like vapour lock.

I flashed your 2024 BIN for the Olds 455 into a bank, same issue.

So now I am wondering if the harness is faulty. The harness came from Speedway PN 91008592 Speedway 1985-1992 GM TBI Engine EFI Wiring Harness   .All the required sensors seen to work fine per the WUD.  It does have additional wires for EGR control, torque converter lockup etc, and they have been left disconnected.

It also has a plug for an oil-pressure sensor which it says Must Be Connected.  This appears to bypass the fuel pump relay, but I've never needed to do this.  It seems the EBL holds the fuel pump relay ON as long as the engine is running, or did I miss something here?

I plugged in another 7747 with EBL with Bins for this engine and it still stumbles, so its not a ECM issue.

How is Valet mode enabled in the EBL?  I'm wondering if some stray voltages induced into these unused wires are causing some weird operation?  Grasping at straws now.

Oh, and while out on a test drive this morning, suddenly the transmission would not shift from first to second... speedo is dead... faulty governor gear. We have a replacement gear, and this thing has headers!!

Any suggestions are welcome.

-- 
Bruce Hislop

[Bill Van Vlack]

Seems like the next thing to check is the harness distributor wiring.

What is this 2024 BIN of which you speak?  (It's too bad the Google Drive associated with this site is no longer available)

Here's the fuel pump/oil pressure portion of EBL's ECM wiring diagram.

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[Bruce Hislop]

Bill,

Changed back to the original HEI that was working on it. So no connection with the EBL.

Powered the distributor with power directly from the main power stud under passenger hood.

Only thing I don't have is an oil pressure switch across the fuel pump relay contacts. Never needed one before. EBL always held the fuel pump relay closed.  But I am going to jump the relay once the engine is running and see what happens.

Bruce Hislop

To view this discussion on the web visit https://groups.google.com/d/msgid/gmcmh-efi/CA%2BX-fMdYp2mEAWuk3F4gjmedge4i4m4O%2B%2BwbmPm_wvenHpSmSA%40mail.gmail.com.

[BruceHislop]

We changed the distributor back to the mechanical HEI because it was working fine, so a known good and eliminates spark control system.  Still stumbles and hesitates

I jumpered the fuel pump relay contacts after starting the engine, simulating having the oil pressure switch in place... still has the same issue.

Last thing we did yesterday was leave the hatch off and remove the air plenum while driving down the road.  When it started to stumble I noticed the passenger side injector wasn't spraying a nice cone.  More droplets and the spray pattern was full of blank areas.  I could not see the driver's side injector as clearly for the air plenum.  So his next step is to have the injectors cleaned.  Its a Holley TB with 80pph injectors which are no longer available.

Anyone know of a Rochester TB from a 454 available for sale?

Bill,  I've attached the 2024 BIN (5 EBL_F2024 BLM INJ 0.bin) which was supplied with the EBL for the Old's 455 from Dynamic EFI.  I thought I'd try a clean slate in case there was some corruption in the BIN file.  Still did the same thing.

Generally the engine will run fine until it gets up to running temperature (but has been known to act-up soon after starting).  When the stumbling and hesitation start, it is usually intermittent, getting worse, the clearing up.  I'm wondering if the new wiring harness is delivering more current to the injectors and pulling the pintiles up further into the injector where they have not been moving to before and getting stuck in built-up gum... maybe.

Bruce Hislop

To view this discussion on the web visit https://groups.google.com/d/msgid/gmcmh-efi/CA%2BX-fMdYp2mEAWuk3F4gjmedge4i4m4O%2B%2BwbmPm_wvenHpSmSA%40mail.gmail.com.

[Jon Roche]

I was thinking it had to be something goofy with the tbi itself or injectors.  

Todd snyder I think posted in the last month or so about a rochester tbi that might of been for sale.   

Otherwise ebay seems to have them but for big $$. 

On Jun 6, 2024, at 6:07 AM, BruceHislop <bhis...@gmail.com> wrote:

 We changed the distributor back to the mechanical HEI because it was working fine, so a known good and eliminates spark control system.  Still stumbles and hesitates

I jumpered the fuel pump relay contacts after starting the engine, simulating having the oil pressure switch in place... still has the same issue.

Last thing we did yesterday was leave the hatch off and remove the air plenum while driving down the road.  When it started to stumble I noticed the passenger side injector wasn't spraying a nice cone.  More droplets and the spray pattern was full of blank areas.  I could not see the driver's side injector as clearly for the air plenum.  So his next step is to have the injectors cleaned.  Its a Holley TB with 80pph injectors which are no longer available.

Anyone know of a Rochester TB from a 454 available for sale?

Bill,  I've attached the 2024 BIN (5 EBL_F2024 BLM INJ 0.bin) which was supplied with the EBL for the Old's 455 from Dynamic EFI.  I thought I'd try a clean slate in case there was some corruption in the BIN file.  Still did the same thing.

Generally the engine will run fine until it gets up to running temperature (but has been known to act-up soon after starting).  When the stumbling and hesitation start, it is usually intermittent, getting worse, the clearing up.  I'm wondering if the new wiring harness is delivering more current to the injectors and pulling the pintiles up further into the injector where they have not been moving to before and getting stuck in built-up gum... maybe.

Bruce Hislop

On 05/06/2024 3:18 p.m., Bill Van Vlack wrote:

Seems like the next thing to check is the harness distributor wiring.

What is this 2024 BIN of which you speak?  (It's too bad the Google Drive associated with this site is no longer available)

Here's the fuel pump/oil pressure portion of EBL's ECM wiring diagram.

<image.png>

To view this discussion on the web visit https://groups.google.com/d/msgid/gmcmh-efi/012da30d-86fb-4fef-837a-decbce225736%40gmail.com.

<5 EBL_F_2024 BLM INJ 0.bin>

[BruceHislop]

Thanks Jon,
I sent a message to Todd about the Rochester.

Bruce Hislop

To view this discussion on the web visit https://groups.google.com/d/msgid/gmcmh-efi/778DF702-FCEB-4552-AA24-C3513172FF68%40gmail.com.

[MICHAEL ORLANDI]

If your Holy TBI body is good you can use a Rochester TBI fuel pod and injectors. It is a little fabrication to fit the pod and to then drill and tap for s carburetor stud.

Sent from my iPhone

On Jun 6, 2024, at 4:07 AM, BruceHislop <bhis...@gmail.com> wrote:

 We changed the distributor back to the mechanical HEI because it was working fine, so a known good and eliminates spark control system.  Still stumbles and hesitates

I jumpered the fuel pump relay contacts after starting the engine, simulating having the oil pressure switch in place... still has the same issue.

Last thing we did yesterday was leave the hatch off and remove the air plenum while driving down the road.  When it started to stumble I noticed the passenger side injector wasn't spraying a nice cone.  More droplets and the spray pattern was full of blank areas.  I could not see the driver's side injector as clearly for the air plenum.  So his next step is to have the injectors cleaned.  Its a Holley TB with 80pph injectors which are no longer available.

Anyone know of a Rochester TB from a 454 available for sale?

Bill,  I've attached the 2024 BIN (5 EBL_F2024 BLM INJ 0.bin) which was supplied with the EBL for the Old's 455 from Dynamic EFI.  I thought I'd try a clean slate in case there was some corruption in the BIN file.  Still did the same thing.

Generally the engine will run fine until it gets up to running temperature (but has been known to act-up soon after starting).  When the stumbling and hesitation start, it is usually intermittent, getting worse, the clearing up.  I'm wondering if the new wiring harness is delivering more current to the injectors and pulling the pintiles up further into the injector where they have not been moving to before and getting stuck in built-up gum... maybe.

Bruce Hislop

On 05/06/2024 3:18 p.m., Bill Van Vlack wrote:

Seems like the next thing to check is the harness distributor wiring.

What is this 2024 BIN of which you speak?  (It's too bad the Google Drive associated with this site is no longer available)

Here's the fuel pump/oil pressure portion of EBL's ECM wiring diagram.

<image.png>

[Bill Van Vlack]

Bruce,

 That BIN has very high VE values - 99's in low speed table, and 100's in high speed - so there's little to no room to add fuel. When I was working with Randy on my setup, he took that BIN and reduced all values by 10 percentage points, raised the former  100% cells to between 90 and 100, and reset the BPC to 148. I ran learns from there, and it's running great.

It's too bad Applied is still sending out this BIN; I understood Randy was going to give them a corrected one to distribute.

Bill

To view this discussion on the web visit https://groups.google.com/d/msgid/gmcmh-efi/012da30d-86fb-4fef-837a-decbce225736%40gmail.com.

[Bruce Hislop]

I never thought about doing that.  Will keep that in mind.

Thanks 

Bruce Hislop

To view this discussion on the web visit https://groups.google.com/d/msgid/gmcmh-efi/62792535-D29F-4A11-8EA0-A9E0564544F2%40sbcglobal.net.