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Author Topic: TBI fuel injection "how to fix common issues"  (Read 1884 times)

zorproducts

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TBI fuel injection "how to fix common issues"
« on: July 22, 2013, 07:20:23 PM »

I will post up a lot of the tricks I have learned on 8v TBI systems. This is how I am writing my repair book. I have no problem with anyone reading this but please do not print without my permission. I am looking for an illustrator to help with this repair book. Ultimately I would like to publish it.
« Last Edit: July 22, 2013, 08:14:13 PM by zorproducts »
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Re: TBI fuel injection "how to fix common issues"
« Reply #1 on: July 22, 2013, 07:35:22 PM »

Problem: Idle is good for awhile but idles down to low after driving for awhile.

Idle screws are not to be adjusted on 91 to 95 TBI systems unless you are prepared to get out the ohm meter and feeler gauges and reset the TPS per book specs BECAUSE you moved the idle screw.

I have an 89/90 bastard EFI (half smart, half dumb ECU). This type has no problem with messing with the idle screw a little. So I turned the idle up and the problem repeated itself. The idle was so slow the oil light would come on. No way the idle screw was moving that quick.

So remembering the most basic cause of idle change is fuel flow change,  I needed to check the injector.

Taking a look at the injector in slow motion. The best way to inspect an injector is to use a timing light. Hook it up as normal and remove the air ram horn so you can watch the injector spray. In my case I was correct. Extra fuel was escaping the injector chamber and slowing the idle way down. In the strobe effect I could see the injector spray was perfect but huge drips were visible coming from the cone. Removing the injector is simple. Just remember that the chamber is high pressure so even with the engine shut off you need to be careful removing the injector from the chamber. Gas in eyes is a bad thing. Once removed the bottom O-ring had a visible crack. Once replaced and back together on start up I had to back off all that idle screw I had added. Got lucky on this repair as no need to readjust TPS.
« Last Edit: July 22, 2013, 07:39:40 PM by zorproducts »
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zorproducts

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Re: TBI fuel injection "how to fix common issues"
« Reply #2 on: July 22, 2013, 08:07:29 PM »

Problem: Idle rpms are going up and down all by itself.

There is a lot of WW2 history here between how much the Japanese learned from the German mechanical engineers. Not sure who invented the variable air leak solenoid but it was a German company. The Japanese applied the technology into what they called "idle air controller" or  IAC. This little bad boy is referred to as the wax plug adjustment. Where the term came from and what it means was lost for all time when Suzuki Dealerships stopped servicing cars.

Math will be required so make sure you know how many rpms you are adjusting. I have seen this issues cause 50 to 400 rpm swings, 800 to 1200 to 800 to 1200 etc.

When you have an idle that goes up a few hundred rpms and then back to where it should be and this repeats, it is time to adjust the IAC spring. Looking at the front of the TBI look for electrical wires to the left that are held down with flexible metal finger tabs. Unbend the fingers and look at the screw holding the tab down. You will notice a Phillips head screw. There are two more in a circular pattern holding a metal cover. Remove all three screws and carefully pry off cover then the paper gasket. Inside is threaded hole with a thread plug. The plug has a special tool to turn it clockwise but you would be surprised to know you have something your box that will work. Adjust it two full turns in or CW. Now put it all back together and check the math to see how the idle changed so you can figure out how much more pressure to apply to the internal rubber plunger/spring.

Math time. Before change idle was 800 to 1100. I adjusted IAC 2 turns and now idle variance is 800 to 900. Math says I need to adjust 1 more full turn.

You should not start engine with the plug cover and gasket removed.
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zorproducts

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Re: TBI fuel injection "how to fix common issues"
« Reply #3 on: July 29, 2013, 08:39:45 PM »

Problem: midrange rpm is adjusting by itself and surging vehicle up and down rpm changes. Most noticable when driving slow.

This issue happens when you have a dead spot in the TPS and the ECU is seeking a signal. I fixed a number of these exact problems by checking the TPS per ohms on A,B,C and D.  Discovering it was bad and replacing the TPS. However, one particular car gave me fits. At 2400 rpm it would stop spraying the injector and turn it back on at 2000 rpm. After 4 attempts of setting  replacement TPS to specs and not getting anywhere. I solved this issue by ever so slightly rotating TPS CW from factory feeler gauge settings. Problem immediately dissapeared.
« Last Edit: July 29, 2013, 08:41:22 PM by zorproducts »
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Re: TBI fuel injection "how to fix common issues"
« Reply #4 on: April 01, 2014, 07:26:59 PM »

Problem: code 31 flashes on very first start up on a used TBI system. Engine was not timed, adjusted, checked just started. Idle poorly and poor acceleration. Removed battery to reset code while I replaced MAP sensor (C-31). Make sure you get black plastic check valve flowing in correct direction when replacing MAP. Started the car and proceeded to fine tune because no code was displayed. Would not rev up. So seeing as I just replaced MAP the component replacement started happening as I was looking for the fix to rev it. I realized I had an issue with idle in that with normal timing engine would stumble and die. So I went back to what causes a 16v to start everytime you turn key but engines stalls on its own (will run if gas pedal tapped). Well that is a defective MAF. A TBI has no MAF but it does have a MAP and even though I had no code I replaced it with another and zoom zoom. Not all components throw codes. So remember, starts up but just dies- What measures M manifold A air P pressure or M mass A air F flow and sends a signal to ecu? MAPs and MAFs fit that bill.
« Last Edit: April 01, 2014, 07:30:01 PM by zorproducts »
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