Need Help w/ SBC 350 TBI

[nicholastheczar]

I'm so f'in pissed. In case you missed the first sentence, I'll repeat it; I'm so f'in PISSED!

Cliff notes version:
SBC 350 w/ TBI with mild RV cam. Has been running rough on start up and rich from day 1. Once warmed up, would run like a top but still rich. Took it to a local mechanic. He told me I needed a new ECM. I bought new ECM. No different, actually ran worse. He told me I needed a new PROM, bought a new PROM from Howell Fuel Injection. I had the wrong PROM in my 7747 ECM. Howell fixed me up and shipped me a new PROM. Installed it and it idled like a freakin' champ, super smooth, like a brand new engine. Take it for a test drive, and it is now backfiring out of the throttle body. Take it back to the shop and tell them what's going on. They call today and tell me its fixed, they adjusted the timing, so they say. Runs great down the road now, but idles rough as hell, and is crazy jerky after you let off of the peddle. The tach is bouncing at idle 300-400 RPMs and will hesitate, and sometimes just die. I hooked up my scanner and all my values are within range EXCEPT for my MAP, it is showing around 10 IHg and the range is 29-48 kPa. Fuel pressure is about 11.5 psi.

I'm pissed that I let these yahoo's work on it because it was running so much better before I took it to them AND I'm leaving for Moab in 2 weeks! Any help is appreciated. And they charged me $300 to make it run worse.

Nick

 

[allan man]

https://forum.ih8mud.com/40-55-series-tech/474702-finally-figured-out-my-sbc-tbi-problems.html

I thought everything went ok......

ohhh ok i get it..... shouldve read the full story.....bummer i would ask for the $300 back

 

[nicholastheczar]

Yea, I thought everything was ok too. I went from excited a few days ago to pissed off today!

Oh, and, yes, I am still f'in pissed.

 

[76 PTO]

You need to datalog and send the data to Brian at TBI chips.com. He will look at the data and burn you a custom chip. Then you will install it and datalog some more. He will keep burning you new chips until it is right. Got mine on the second try perfect.

 

[nicholastheczar]

On my MAP sensor, it reads out in IMg (inches of Mercury) and gives the range in kPa (kilopascal). When I converted it, my 10 IMg is equal to 33.83 kPa and the range is 29-48 kPa, so I am within range. Don't know what else to look at.

I'll call Brian tomorrow and see what he can do. Thanks.

nick

 

[Martytheretireeeee]

Sounds like you may have an ignition problem. You did'nt mention year of engine or type of distributer. If it is electronic your pickup coil may be shot.

 

[Elbert]

do you have a timing light...? what is your base timting set at with the jumper wire disconnected?

Assume you have not check engine light on, no trouble codes either?

 

[nicholastheczar]

Best I can guess is the motor itself is out of a 78-79 chevy 5.7L. My throttle body is from a 88-89 chevy suburban 5.7L. My distributor is from Napa for the same year (89 chevy 5.7L w/ TBI). How do I test my coil?

nick

 

[Martytheretireeeee]

Sorry it took so long getting back to you but I lost service due to a rain storm.

Remove the distributor from the engine.
Remove the rotor and disconnect the pick-up coil leads from the module.
Checking
Connect an ohmmeter to each terminal of the pick-up coil connector or wire and ground (one terminal at a time). The ohmmeter should indicate infinite resistance. If it doesn't, the pick-up coil is defective.
Connect the ohmmeter between both terminals or wires of the pick-up coil connector. If a vacuum advance unit is attached to the distributor, apply vacuum from an external source and watch the ohmmeter for indications of intermittent opens (if no vacuum unit is used, flex the wires by hand). The ohmmeter should indicate one steady value within the 500 to 1500 ohm range as the wires are flexed. If it doesn't, the pick-up coil is defective.
If the pick-up coil fails either test. replace it.
Replacing
Mark the distributor shaft and gear so they can be reassembled in the same relationship.
Secure the distributor shaft housing in a bench vise and drive out the roll pin with a hammer and punch.
Remove the gear and tanged washer, then check the shaft for burrs. If none are found, pull the shaft from the distributor.
Remove the three attaching screws and separate the magnetic shield.
Remove the C-clip and detach the pick-up coil assembly.
Install the new pick-up coil assembly and make sure the C-clip is seated in the groove.
Install the shaft. Make sure that it's clean and lubricated.
Install the tanged washer (with the tangs facing up), the gear and the roll pin, using the mark you made earlier to put it back in the same position.
Spin the shaft to make sure that the teeth on the distributor shaft don't touch the teeth on the pick-up coil pole piece.
If the teeth touch, loosen, adjust and retighten the pole piece to eliminate contact.
Install the distributor in the engine.

Hope this helps!

 

[nicholastheczar]

I do have a timing light. I'm going to check my timing today. Last night I rebuilt my fuel pressure regulator in my throttle body hoping that would help. Nada.

I do not have any trouble codes.

Nick

 

[nicholastheczar]

I spoke w/ Howell fuel injection this morning and they ran through all my readings with me on my scanner. The only thing they said that is out of spec is the Block Learn, which at idle during closed loop is 108. As soon as I give it gas, it jumps up to 124-128ish, but if I let of the gas, it drops to 108. All my other sensors are where they should be according to my scanner range and Howell. They told me to set my timing at 10* before TDC, which I did.

Howell had me restrict my fuel to about 9psi to see if that improved my block learn, but it did not.

I thought SBC TBI motors wanted around 12psi of fuel delivery? Maybe a new fuel pump? Its only a year old. I just hate throwing money at something when I don't know if that is the problem or not.

Nick

 

[Martytheretireeeee]

Your ECM is the brain of your TBI system but the pickup coil in the distributor is the nerves of the system. The pickup coil (not to be confused with the ignition coil) sends a signal to the ECM telling it which cylinder to send fuel to and fire. If the pickup coil is "faulty" the ECM gets confused and can send fuel to the wrong cylinder and tell another cylinder to fire. I use the word "faulty" because sometimes it won't just stop working. Over time the wires in the coil will overheat and the paper coating around it will bubble and then the wire starts to break or fuse together and the problems start. This is a cheap fix, about $15 to $20 for the pickup coil and the distributor control modual both and most people replace them both at the same time.

 

[nicholastheczar]

I guess I don't know which one is the pickup coil vs. the ignition coil. I have a pigtail that comes from my tbi harness. This plugs in to a coil next to my distributor. one of the wires from the distributor goes to this coil. Is this the pickup coil?

I've also taken my timing to about 12* BTDC and my idle has smoothed out somewhat and my block learn numbers have gone from 108 at idle in closed loop to around 113. Getting closer.

nick

 

[nicholastheczar]

Is this my pickup coil with the red label?

 

[GreaseMonkey]

Hum, this may not be relevant, but I had similar symptoms on my brothers 4.3 with TBI. And I thought at first that the timing had skipped as I had just replaced the timing chain and a lot of other goodies. Then I noticed that the EGR valve (which is an old vaccum biscuit on his '93 Chevy) was in the open position when the engine was off and there was no vaccum. Grabbed needle nose pliers and gently persuaded it to close, and then soaked it with ZEP 45. Problem solved. Something to check anyways.

 

[nicholastheczar]

Hum, this may not be relevant, but I had similar symptoms on my brothers 4.3 with TBI. And I thought at first that the timing had skipped as I had just replaced the timing chain and a lot of other goodies. Then I noticed that the EGR valve (which is an old vaccum biscuit on his '93 Chevy) was in the open position when the engine was off and there was no vaccum. Grabbed needle nose pliers and gently persuaded it to close, and then soaked it with ZEP 45. Problem solved. Something to check anyways.

I don't have an EGR valve. The PROM that I ordered from Howell was for sbc's w/ the EGR removed. I have 2 ports on the front of my throttle body that are capped. I'm assuming one of those was used for the EGR.

nick

 

[Martytheretireeeee]

No, the pickup coil is inside the distributor and it is round with a hole in the middle. The distributor shaft runs through the hole and it is about the size of a 50 cent piece 1/2 inch thick with two wires and a connector. Autozone or any parts store should have a diagram showing the part and its location, if you take your distributor # to napa they should be able to help you out. As far as I know the contol module can't be bench tested. Good luck. Sorry about my last post, I mixed a little multi port info in.