TBI wouldn't start, but now does?

[scorp1us]

I've been tuning my TBI system and it's been good. I added some timing to the lower end and she dieseled (very, very brief) after I turned her off last night after a short run. An hour later I went to start her and nothing. She'd crank over but it was like there was no spark. She had fuel and air, but didn't have time to pull a plug before I had to go with a back up plan and be some where. About 2 hours later I come home and crank her some more, one spark in a few cranks and closed it up for the night. This morning I go out and she starts right up.

I'm thinking this is from the ignition module. Is this how they go up, or was she just too hot to run with my current program?

[Bill usn-1]

Ignition module is possible but it doesn't sound like it if you said you have fuel.
You won't have fuel spray without having spark.

Sounds more like you were flooded and needed to hold the pedal down for clear flood mode.

How much timing are you running at idle? 10-15* is about all you need.
So normally the timing remains the same from 400-800 around the idle map so the idle stays constant.

The 7427 also uses adder tables to adjust the idle timing to help maintain a steady idle.
The tables and when they are applied can be adjusted.

[Eric VanBuren]

Why would you have to pull a spark plug to check for spark, that won't really tell you anything. To properly check for spark you need to pull the coil wire and hold it with a minimum 1/4" gap to a good ground.

What coil are you using the GM TBI unit? If so it is not uncommon for them to develop internal shorts that reduce their potential output considerably. Sometimes they'll do it when hot and be fine once they cool back down.

As Bill mentioned if you have fuel spray the pickup and module are working however that does not mean that you have spark that is strong enough to start and run an engine. To verify spark that will start and run the engine see the test above.

[scorp1us]

I verified fuel and air by unscrewing the IAC and looking at the injectors as I cranked. They sprayed and I could hear the sucking sound from the IAC.

The last time I held a plug wire it hurt a lot.

I'm using the used GM coil that came with my kit.

I was running 15.1, but as part of my low-end tweaking I bumped it to 16. Basically for any cell that had enough samples and 0 knock retard, I bumped the timing 1degree, and was going to keep doing that until I was getting a little knock in every cell, then back it down a tad. (.5 degree or so)

[Bill usn-1]

I feel you plan for timing is a little flawed.
i don't think you will ever see ping under no load conditions.
So you basically need to cut your timing table in half and only work on 60-100map and 1000rpm and up.
If you have an auto then the stall speed is about 1600-1800rpm so there will be very little load till then.

If you go too high in the no load areas it will just increase heat as the spark fires before the piston reaches the optimum hieght in the cylinder.

If you have the GM ignition and GM coil then you will get at least 1/2" of blue spark.
As long as the spark can jump to ground you will not get shocked.
If you pull it too far away then it will look for the shortest path to ground. So hold the wire father back from the tip.

[Eric VanBuren]

Originally Posted by Bill usn-1

If you have the GM ignition and GM coil then you will get at least 1/2" of blue spark.

IF the coil is working properly if it has an internal short they I've seen them only able to jump about the gap of a spark plug which in free air is not enough to start and run the engine.

Originally Posted by Bill usn-1

As long as the spark can jump to ground you will not get shocked.
If you pull it too far away then it will look for the shortest path to ground. So hold the wire father back from the tip.

Personally I try to position it someplace where it will lay with the gap and not hold the wire directly when checking for spark, if the insulation is weak where you are holding it your body may be a better ground than that 1/4" air gap.

[Bill usn-1]

I have my son hold it and then tell him to move it farther away until he yells!!

[Eric VanBuren]

Originally Posted by Bill usn-1

I have my son hold it and then tell him to move it farther away until he yells!!

That's one effective way to do it. The louder he yells the stronger the spark?

[scorp1us]

Bill, thanks a million for the info! Some questions remain.

Originally Posted by Bill usn-1

I feel you plan for timing is a little flawed.
i don't think you will ever see ping under no load conditions.
So you basically need to cut your timing table in half and only work on 60-100map and 1000rpm and up.
If you have an auto then the stall speed is about 1600-1800rpm so there will be very little load till then.

If you go too high in the no load areas it will just increase heat as the spark fires before the piston reaches the optimum height in the cylinder.

Done. I backed out most of my changes. (Which were under 50map and under 1000rpm) I swear I was seeing more torque off the line though...
I thought that was knock? What about being under load makes it different?
What is a fair amount of knock? I'm using the knock retard average value? I'm shooting for 0.1, so I just see some. can i safely go more?

Sounds more like you were flooded and needed to hold the pedal down for clear flood mode.

How would this happen on an EFI? The vehicle sat for ~2-3 hours. This should have been long enough to clear the intake, no?

[Bill usn-1]

Your timing below 1000 may be helping your initial launch a little.
What you need to do is start really looking at the data avail.

If you use the monitors to display rpm, timing, map, knock/retard then you can play the recording and watch the values together.
Then watch your spark adv or knock table as it fills in.
You should be able to see a pattern how the highlighted cell moves as you hit the throttle.
It normally travels in a diagonal from idle to the lower right.
So that will show you exactly what cells you are actually using during acceleration.
If you do that with each type of driving, you can adjust the timing for each specific are instead of just adding timing everywhere and seeing if it's better.

Add into the mix PE mode depending on how you have it set, adds timing and fuel.

You will need to compare the knock counts in those specific cells after each adjustment.

Keep in mind that WOT 100 map is about 32*
your highest timing will be under light cruise where you normally drive down the hiway at 60mph. Most bins are set max timing at 41*


EFI can flood when something is not right!
With the condition you described the IAC could have also got lost. So it could have been completely closed giving the engine all fuel and no air or completely open giving too much air.

If you have driven the IAC closed then you know the next time you try to start it takes longer until the IAC resets.