TBI has me ready to blow it up

[Element]

Only GM could design a fuel injection system that NEVER works right.

So, new problem with the pile of junk GM calls an engine in my truck. Idles fine. Runs fine. Come to a stop, it feels like it only runs on 2 or 3 cylinders. Drop it in idle, rev it a bit, it comes back to normal and idles fine. This comes after the truck runs fine for 3 weeks, no changes to ANYTHING on the truck, starts doing it out of nowhere.

I'm really, really close to finding a 5.3L or a 6.0L (LQ4 or LQ9), pulling the 4L60E out of my old S-10, and dropping that into the Blazer. This TBI s&%$ is just ridiculous.

New parts? If you ask, it's probably been replaced, and with as much as I've put into this gutless engine, I could have had a 6.0L sitting in my garage.

 

[ryoken]

my tbi runs great... has for years... it's not rocket science...

 

[Cricket]

How old is the fuel pump, could it be getting weak? Do you have a fuel pressure gage inline near the throttle body you can watch while having somebody put it in drive at idle?

 

[Jason4x4]

Bad Booster? sucking air, making it run too lean?

 

[Element]

How old is the fuel pump, could it be getting weak? Do you have a fuel pressure gage inline near the throttle body you can watch while having somebody put it in drive at idle?

Brand new fuel pump, sending unit, and filter. Pressure was checked when the pump was put in and it was good.

 

[Element]

my tbi runs great... has for years... it's not rocket science...

My SFI car runs high 11s, I can work on it fine.

This thing? Replace part after part (because the archaic computer won't flash a code when the damned thing won't even run right) and it still doesn't work right.

I don't get it.

 

[Element]

Bad Booster? sucking air, making it run too lean?

No vacuum leaks, nothing like that I can hear. It just started doing this out of the blue one day - ONLY when coming to a stop. Any other time, it runs fine.

 

[Cricket]

Hmm...well I feel for you. I've had a code 32 for 2 years that no one can figure out.

It can be pretty frustrating. Without a scanner or WinALDL your just guessing most of the time. If you have the ability to get a cheap laptop and hook up WinALDL you might get lucky and record the glitch while driving.

 

[Element]

Hmm...well I feel for you. I've had a code 32 for 2 years that no one can figure out.

It can be pretty frustrating. Without a scanner or WinALDL your just guessing most of the time. If you have the ability to get a cheap laptop and hook up WinALDL you might get lucky and record the glitch while driving.

Well, I've got a code thing (plastic handle with the 2 little prongs) but the truck isn't throwing any sort of code at all, nothing. All the problems I've had with it, it's NEVER thrown a code. I'm just a lot more used to working on OBD2 cars that toss a code as soon as the most minor sensor has a fluctuation.

With this thing, as soon as I get one issue fixed, something else comes up.

 

[sarasotausmc]

Mine throws intermittent codes all the time. Other day, I got a 13/42, cleared it, then a 24, cleared that, then 42, said f it and left it. Came back, cleared that, and came back with a 13.

Replaced the O2 sensor and all is good.

One other thing I did is disconnect ALL of the sensors, cleaned the contacts and plugged them back up. Checked my grounds and plug wires. It's running like a champ now.

It's frustrating and sometimes confusing, but can be done. I feel your pain.

 

[dyeager535]

Does it idle bad in park/neutral as well as drive, or only with the load on the engine?

How is idle quality when it's running "right"? Perfect, or RPM varies, lopes a bit, etc?

 

[Element]

Does it idle bad in park/neutral as well as drive, or only with the load on the engine?

How is idle quality when it's running "right"? Perfect, or RPM varies, lopes a bit, etc?

The idle, when I come to a stop and it starts screwing up, does it regardless of what gear the truck is in - park, neutral, drive, reverse.

It idles a bit weird when cold, but I expect that, it's an old engine - some surging and about 1100rpm until it's run for 3-4 minutes. When it's idling "normally", it's fine - typically stays right at 600-700rpm, flat, no surging or anything.

 

[nad]

You mean you can read engine codes on these old trucks? How about carb'd motors?

 

[Thunder]

You said you dont get any trouble codes? You should always get a code 12 when you check trouble codes. If you dont get a code 12 there are probabally problems with the ECM. Does the check engine light operate? Does the CEL come on when the key is on but engine is not running?
Have you checked and cleaned the IAC and EGR valve ?

TBI is a good, simple, and reliable FI system. GM used it on millions of cars and trucks from 1982 to 1995. Gutless??? TBI makes more horsepower and torque in trucks than the eariler carbed trucks. I find TBI very easy to work on and trouble shoot. But you really need Win aldl or a good scanner that gives you real time operating data. Those cheap little code readers you buy are worthless. You can do the same thing they do with a paper clip for free.
You cant work on most modern SFI OBD2 cars without a good scanner. TBI/OBD1 is no different. Buying a scanner is a lot cheaper than needlessly replacing good parts and sensors

 

[Element]

You said you dont get any trouble codes? You should always get a code 12 when you check trouble codes. If you dont get a code 12 there are probabally problems with the ECM. Does the check engine light operate? Does the CEL come on when the key is on but engine is not running?
Have you checked and cleaned the IAC and EGR valve ?

TBI is a good simple FI system. I find it very easy to work on and trouble shoot. But you really need Win aldl or a good scanner that gives you real time operating data. Those cheap little code readers you buy are worthless. You can do the same thing they do with a paper clip for free.
You cant work on most modern SFI OBD2 cars without a good scanner. TBI/OBD1 is no different. Buying a scanner is a lot cheaper than needlessly replacing good parts and sensors

I get code 12; I had to pull the dash and replace the little bulb socket previously, but it works now. i just don't get any error codes, other than the generic 12 code.

IAC and EGR are both new. EGR was giving me issues previously, but I replaced it.

TBI is to me nothing more than a computerized carb. SFI and MPFI does require a good tuning program, but they're also a lot more advanced and tuneable. Don't know, I just don't like the system at all.

 

[stockk5]

i understand your pain with tbi.. for about a month after i swaped in my new engine.. my truck came w/ tbi original and was putting a new motor for tbi in.. i thought everything was fine, but the injectors were not getting pulse.. went nuts finally just wiggled the wires behind the block one day.. fixed it.. then would stall randomly, it pissed me off for ever, took months and months, replaced tons of things, ingition module, coil, tps, everything. ended up being my fuel pump relay wasnt completely plugged in.. this is after so much harassment from all my friends saying to just put a carb on it. so yes.... i hated my truck for a while.. and yeah tbi wasnt so fun. runs great now.

 

[oldtoyboyd]

Get a scanner hooked to it so you can look at O2 sensor data and see what fuel trim looks like to know if the computer is going rich or lean.
Daniel

 

[Thunder]

Its hard to diagnose stuff over the net. But for idle problems many times there is a problem with the TB. The TB base gasket is a common problem. They get old and leak. I have replaced mine on my K5 twice.
Injectors get worn out. IMHO If you have over 100K on injectors of any kind they should be replaced for best performance.
I put a flow matched set on my K5 and it made quite a bit of diference. Even tho my truck ran good with the orginal set, the new injectors smoothed out the idle and gave better overall performance.

The throttle shaft bushings wear out and can affect the idle but usually the IAC can compensate for that small of an air leak.

You can try to reset the base idle. and check the TPS voltage.
heres how.
• Jumper pins A&B on the ALDL (Assembly Line Data Link) connector under the dash. Pins A&B are on the upper-right-hand side. These are the same two pins to jumper to read codes from the ECM.

• Now turn the key on (the Check Engine light should be lit) and leave the key on for at least 30 seconds. The computer will extend the IAC plunger all the way out to allow adjustment of the idle speed.
• After the 30 second wait, unplug the IAC (square 4-pin connector on the throttle body) WHILE THE KEY IS STILL ON. This prevents the ECM from adjusting the idle speed while you make your adjustments.
• Block the drive wheels, set the emergency brake, and start the engine. Set the idle speed by adjusting the idle speed screw. The engine should be at operating temperature for this. The exact setting is on the emissions label on the radiator shroud, but in general, the idle speed should be about 500 RPM in Drive, 700 in Park / Neutral, or if you have a manual transmission, somewhere between 600-800 RPM. Remember that the truck is running during this adjustment, so stay clear of the fan, and make sure it can't roll or otherwise be put into gear while this is done.
• Once the minimum idle speed is set, turn the engine off, reconnect the IAC, and remove the jumper from the ALDL connector. • The TPS minimum voltage must now be set. Turning the idle-speed screw may have moved the TPS idle voltage away from the specification, so it should be adjusted next. Connect a voltmeter between pins A (usually black) and B (usually blue, or green) of the TPS, and turn the key on. Don't start the engine. Loosen the two torx screws holding the TPS in place, but don't remove them. Rotate the TPS until the voltmeter reads between 0.45 and 0.55 volts, with 0.50 being ideal. Tighten the mounting screws (carefully, they thread into soft aluminum) and re-check the voltage to make sure it's still within range.

Hope this helps a little.