1989 Silverado 454 ECM Bad Ground?

Tim Rif · 03-10-2006, 07:35 PM

Has anyone out there heard of the possibility of a bad ground (to the engine) that can affect the computer (ECM), and cause the engine to intermittently run rough and cause an occasional SES light? I have had the truck to 2 different shops and they can't find anything wrong. The engine only has 50 miles on it (rebuilt 454 long block). I had the injectors rebuilt, all new tune-up parts, EGR, O2 sensor, it has good fuel pressure, and the thing still doesn't run right. It idles rough, throws an occasional 44 code (lean exhaust), and acts like it has a bad accellerator pump, but it has TBI. The only thing I can think of is maybe an electrical problem such as a bad ground, because other than a rod knocking, the truck ran pretty good before the engine swap. Would the dealer be able to diagnose the problem? Thanks....Tim

Hammer59 · 03-10-2006, 10:28 PM

Check the ground on the back of the cylinder head. Also check your tps for
.65v. you will need an ohm meter to check it. If it's out of range it will throw the 44 code an run like crap.

Hammer59 · 03-11-2006, 11:25 PM

Have you checked for vacuum leaks?

Tim Rif · 03-12-2006, 01:03 PM

I don't see any vacuum leaks. I sprayed carb cleaner all around the engine and the idle didn't change. Is the voltage on the TPS .65v? I read somewhere it should be .45-.55. Right now it is at .51v

Hammer59 · 03-13-2006, 09:29 AM

Are you using the tbi unit that was on the truck before you rebuilt the motor?
Is the motor popping when you accelerate. Give us more info on the motor rebuild.
Stock cam and heads? It could be a bad ground but you're not giving much info.
What's you're timing set at?

Hammer59 · 03-13-2006, 09:32 AM

Quote:

Originally Posted by Tim Rif

I don't see any vacuum leaks. I sprayed carb cleaner all around the engine and the idle didn't change. Is the voltage on the TPS .65v? I read somewhere it should be .45-.55. Right now it is at .51v

The best way to check for a leak is with a vacuum gage.

Tim Rif · 03-14-2006, 08:44 AM

It is a rebuilt long block from S&S engines in Spokane, WA. I had them put an rv cam in it, but other than that, it is stock. It is the factory replacement for that year and truck model. It may have came stock with the rv cam because it is the same engine GM used in the motorhomes for those years. I keep getting a 44 code which is lean exhaust, or low O2 sensor voltage. I'm not sure what the voltage is suppose to be at the sensor (I heard around .5v-.8v), but I am only getting .1v. Even when I unplug it and check the voltage I'm only getting .1v. I suspect the low voltage is causing a problem, so I need to determine why the voltage is low. Bad ECM ground or bad ECM? When I checked the voltage at the O2 sensor, I just grounded to exhaust manifold, so maybe the exhaust manifold is not grounding properly. I will try grounding right at battery and see if I am still only getting .1v at O2 sensor, and post the results. Feel free the provide suggestions in the meantime. Thanks, Tim

Tim Rif · 03-14-2006, 08:48 AM

I forgot to mention that it is the stock TBI. I'm not sure what the timing is set at (I had a shop set it), but I will double check that too. Tim

Hammer59 · 03-14-2006, 11:07 AM

Do you have the specs on the rv cam? It may require a custom chip to make it run properly. Contact Brian at www.tbichips.com

Rs051802 · 03-18-2006, 10:36 AM

Quote:

Originally Posted by Hammer59

Check the ground on the back of the cylinder head.

This will cause the engine and ecm to perform very poorly. If you have not checked it, I would highly recomend

Tim Rif · 03-18-2006, 04:14 PM

I checked the all the grounds and tugged a little on the one going from the firewall to the back of the engine ( to see if it was tight), and it broke off the back of the engine. I assume that ground wasn't working and it definitely isn't working now. The grounds from the battery to the body, engine and frame appear to be good, so I don't know see how the wire from the firewall to the engine could cause a problem, but then again, why would it be there if it wasn't necessary? Right now the truck is in another shop. Once again, they noticed a terrible spray pattern with the injectors. I had them rebuilt, checked and re-checked, and Doctor Injector swears the injectors are fine (atleast when they leave his shop). The shop where it's at now says when they sprayed propane into the TBI the engine smoothed out. They did a smoke test and noticed a small vacuum leak around the TPS solenoid. Also, they mentioned the fuel lines to the TBI looked a little rusty inside. Then again, maybe this is just info they are telling me to justify there $72 an hour. I replaced the fuel filter after I swapped engines and I could not blow through the old one, so I assume it was plugged. Other than the rod knock, the old engine seemed to idle pretty smooth, but then again, I didn't drive it, or run it very long. What it boils down to, is the engine is starving for fuel and throwing a 44 code (lean exaust). Whether or not it is caused by the vacuum leak or dirty fuel lines or a confused computer remains to be seen until the vacuum leak is fixed.

Hammer59 · 03-18-2006, 05:38 PM

The rates these shops charge are down right robbery.
I hope it doesn't cost you much.
take care.

Rs051802 · 03-20-2006, 09:49 PM

The wire from the head to the firewall is an ecm ground. If the fuel lines were rusty on the inside you would get some rust spraying into the injectors. If the line was clogged or even collapsed the truck would not run at all. I would fix the vaccuum leak on the tps solenoid and see what that does. Get a can of Berrymans Chemtool carb and injector spray and while the truck runs spray it all around the intake, all vaccum lines and fittings. If the truck has a vaccuum leak it the Chemtool will bog the motor down when it touches the leak. If the tbi has rust in it pull it off and clean it out definately! If you have access to a timing light check your timing. The shop that set it may not have unplugged the advance. This will cause the truck to run rough. Good luck and keep us posted.

failfree · 08-19-2018, 08:53 AM

Were you able to get your vehicle fixed? What was the solution? I am dealing with the SAME issue. The last straw is to replace the ECM.....thoughts?

fast68chevy · 12-26-2018, 11:33 AM

bad ground wires connection yes, also vacuum leak intake or TB unit base etc. bad sensor TPS or EGR or such, check voltages and grounds 5volts and grounds at sensors. and for .5 to 4.5 volts at TPS full range, closed to open WOT, and wiring connector pins connections and so on also.. failed ECM ix last thing to happen and rare, most rare especialyl the 7747 ECM, they are really sturdy reliable, unless a circuit gets ground or hot shorted. or a capacitor blows(usually/typically can visually see a damaged or burnt or expanded blown up cap) happens on the 90s ford trucks injector modules alot.. burnt blown capacitors there are three caps on those fuel modules in the ford trucks. and they love to burn up and cause stall and no start. but this isnt a very common GM issue at all.

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