Checking TBI injectors

00fxd

00fxd

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Can anyone help me? I have a late style Holley 502-6 TBI on my sb400. Driving the car the other day it ran rough for a few minutes then cleared up. Today I was going out in the car and it ran crappy right away. With a lttle looking I could see that the left injector wasn't injecting. Can I check continuity between the terminals of the injector to see if it's ok? Can I run it and check for voltage at that pigtail. Any idea's what else I should look for?
Thanks, Frank.
 
Look for resistance between the two terminals of the injector. I think a high impedance injector should be ~10-14ohms. Anything more that that and the injector is probably toast.
 
Thanks for the QUICK reply Shark. Been unpluging and checking connections. I went out and checked the resistance, it's the same for each injector. I flamed her up and checked the voltage at the offending injector pigtail - 6ish volts. Plugged it all back in and it's all fixed. Nice cone. Whats with that?...... Guess I won't go too far from home for a while.
 
Dirty connection most likely, the injector driver in the ECU triggers the ground, the 5V is constant. Usually the 5V is fused somewhere.
 
Thanks for the reply twin turbo, Sorry I didn't respond, the site didn't notify me.

So I go to go out today to go for a ride, the cars starts and warms up ok and then begins to car miss on that injector again.
Any idea's anyone?
 
It may be a soldering break in the ECU resulting in the driver being cut off.

Swap the 2 connectors and check again if this time the other injector craps out
 
Wow, fast reply again as well as a great idea. I was just looking for a spare ecm that I have but I can't find the g.d. thing anywhere.
Thanks again
I should also note, no codes.....
 
Twin Turbo - I switched injector plugs and the offending injector worked and the other one quit. Thanks for the suggestion.
So where the hell is my spare ecm ?? I'll go buy one tomorrow so I can find my missing one the next day.
I hate that......:lol:
 
So, when the injector is not firing, you do have 5V? If that't the case, and the error being unpredicatable as it is, I'm betting it's a soldering break on the board near the injector driver.
 
So..... Just for fun I'll follow up. Lots of responsibilities to do at work today so I got up and was at the auto wrecker when they opened. That didn't go well, they couldn't find the one they thought they had so we dug though old shit till we luckily[?] found one. I took it home, went to work and put out needless unexpected fires all day. Big problems but it all worked out thank God [so far]....
So I go ahead and installed the replacement ecm with my custom prom and got check engine light flashing crazily. So I check codes, code 51 - bad or improperly installed prom. Disconnect batt to clear codes. Try again, flash crazily, code 51. Re install and check, flash crazily, code 51. Try orig ecm with stock prom, flash crazily, code 51. Try running car, batt dead. Charge batt, take car for drive, runs like shit, limp home mode I think, light flashing crazily. :sos:
Install original ecm with my original custom prom, runs great, no check engine light, put car through paces, off season mods working great, corners beautifully,....... get speeding ticket, come home and write this report and go to bed. :censored:
 
Thanks T_T we posted at the same time. Every time I've checked voltage at the injectors I've had the 5-6v
 
Guys, all my ECM design experience is with PFI/SFI systems, but there are a couple of older TBI ECM items mentioned above that appear different than my recollection.
TBI injectors are generally driven by a ramp and hold circuit, rather than a saturated switch circuit like in high impedance (injector) systems such as PFI systems. BBShark is correct that high impedance injectors are around 12-14 ohms (roughly an amp of current through the injector coil). TBI injectors are, IIRC, low impedance, about 2-3 ohms. The ECM drives the injector from a battery (12v) source. Once the TBI injector current hits about 4 amps (assuring quick, complete opening), the ECM driver circuit will then reduce the current level to a holding value of about 2 amps, reducing the power dissipation in the injector.
I don't know what specific ECM the OP is using, but I welcome any correction if I have misstated anything here.
 
Thanks 69427, I really appreciat your input. I am using the most common ecm, the7747 and all of the sensors from a '90 chev 4x4, manual trans. I modified the harness very correctly myself I belive, retaining the aldl plug. I added a speedo cable driven 2wave speed sensor. The tbi is the holley large bore that is the same size as the 454 truck tbi. With a mail order prom, it runs very well. This was ment as an exercise to get this old guy into the world of modifying efi and I had intended to get into prom tuning. Now my direction is to move up to an LSx engine shortly.
Do you have any comments on my above mentioned 'symptoms'?
 
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Wait a minute, it's a holey TBI, I only noticed TBI at first. Doesn't the holley system use the chrysler style (egg) injectors?

The Chrysler TBI injectors are peak & hold units also if I'm not msitaken. 1227747 is a commonly used hacked TBI ECM, also a peak & hold (of course) system, much like the GM 1225550 and later TBI ECMs
 
Twin_Turbo said:
Wait a minute, it's a holey TBI, I only noticed TBI at first. Doesn't the holley system use the chrysler style (egg) injectors?

The Chrysler TBI injectors are peak & hold units also if I'm not msitaken. 1227747 is a commonly used hacked TBI ECM, also a peak & hold (of course) system, much like the GM 1225550 and later TBI ECMs
Click to expand...

Hi T_T. Yes the early Holey tbi's of that model used the Chysler style injectors. They had problems with them. Mine is the later model that uses injectors that interchange with the GM units I belive.
 
00fxd said:
Thanks T_T we posted at the same time. Every time I've checked voltage at the injectors I've had the 5-6v
Click to expand...

I'm confused about the 5-6 volt reading. I'm guessing that is the voltmeter averaged reading at the injector low side (ECM side) when it's running. (Correct me if I'm wrong about how you measured it, as there should be 12 volts at both injector terminals when the injectors aren't firing.) Just curious.
 
You're right, it's 12V

Here's the complete mapping of the 1227747 connectors & voltages

2482f3f27e4865.gif

Here are the 84 C4 ECM and the 82 1225550

2482f3ff62b6cc.gif

2482f401159be1.gif
 
When I had one 1 injector firing I checked the pigtail on the other one for voltage when the engine was running. When T_T gave me the good idea to swap connectors I checked the other when the engine was running. That was several days ago but I expected 5v so I wasn't supprised when I thought I saw my digital meter show 5-6v. I could check again later.
Thanks again, Frank
 
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