Pablo

iTrader: (1)

may sound like a dumb question but how do I do this? I have a DMM that supposedly measures duty cycle but im not exactly sure how to hook it up. Do i put the "+" lead on either side of the injector and the negative just to a ground or do i put both leads on there one before and one after the injector.

this is on a 7747

reason I ask is because I am once again trying to figure out why my injectors arent firing during crank. Now im tackling it like a science project.
The one thing I know for certain is that the power to the injectors is there. Now for whatever reason I suspect the ecm isnt telling them to fire. But I want to know for sure it isnt some fluke thing like the injectors are bad and require alot of voltage to fire that they arent getting during crank but do get during run.

Grumpy

Duty cycle is the same as taking a dwell reading, your reading the period of time when the points are closed or in this case injectors grounded, by the ecm.

Whithout knowing the sampling rate of what you have, it might be too slow to catch the injector firings. Best/easiest thing to do it find another EFI car, and see what sort of readings, if any, you get on it, then try it on yours.

A analog *needle* type meter should catch it at cranking speeds.

A Noid light is handier, IMO.

onebinky

iTrader: (1)

What about a logic probe? Or is that the same as a noid light? I know you can get a decent logic probe for about $20 from radioshack. It's real time and has high internal resistance so it wont fry the injector drivers

jeepguy553

Would a DVM set in BEEP continuity mode do the same thing? I am assuming you have TBI...have you checked the fuel pressure regulator to see if it is delivering fuel to the injectors? A $20 rebuild kit may be in order here. I wouldn't be so quick to blame the ECM for the lack of fuel.

dimented24x7

iTrader: (2)

Another thing you could do is use some LEDs w/ resisters in series and then hook them in alongside the injectors. Should be able to see them blink quite brightly when the injectors fires and there is the full 12 volts.

Pablo

iTrader: (1)

theres alot more to this story than what you see here, I had a long thread about it a couple months back. Basically the car will run fine with the TBI if i can get it started. It will not deliver fuel in crank but it delivers fuel in run, and sometimes as im turning the key from on to crank it will squirt fuel and as im letting off it will squirt fuel. This has been enough to start it and once it starts it runs fine. Its not a power problem to the injectors the power is there (8.5 volts at the injector terminal during crank) either the ecm is just not grounding them or the injectors wont fire at 8.5 volts. I dont think theres anything wrong with the ecm or proms i have tried several proms and have two ecms.

The car runs fine with the carburetor and the ecm controlling the spark. I am just tired of the carb and want my FI back.

I just want to rule out injectors at this point (btw the resistance across both injectors is within spec)

As far as a noid light is concerned, I take it that is a slang name for a specific tool because I went looking for a "noid light" and could not find one. I found a solenoid tester of some sort which I suppose is probably what you are talking about but it didnt look like much more than a fancy test light. I was figuring it would need like an LED to react fast enough... do they react fast enough?

ben73

You need to use a dmm that has a frequency (Hz) scale.
This will tell you the rate of injector pulsing.

Grumpy

A Noid Light is a specific tool. Around here, AutoZone carries them in the diagnostic tool area.
It's basically a large bright LED.
It's just convient to use since it has the injector type connection on it, they have them for TBI, Port, injectors, and IACs.

Grumpy

Pablo

iTrader: (1)

ahhh that clears things up. I will look for one. thanks

JPrevost

I can't find your old post but have you checked the ecm pin for cranking? When you crank the car the ecm needs to know you're cranking (digital in) and then it commands the richer AFR. Just an idea. Like grumpy said, get a car that has a running TBI and plug in your injectors, if they fire... then switch out your ecm, your eprom, etc. Check all the pins on the ecm. Might also want to check the "min TPS to clear flood." I don't know if it were set at zero if it would always be commanding the clear flood AFR but it's just an idea. Good luck.

Pablo

iTrader: (1)

well the crank input coming off the crank fuse (D9 i think on the ecm) wasnt getting power during crank, I fixed that and now it gets like 6 volts while cranking (dunno if thats too low) its not a digital signal its just voltage. It didnt change a thing as far as the injectors were concerned, the problem still persists.

Are you maybe talking about another pin on the ecm?

dimented24x7

iTrader: (2)

Hmm... good question, is the signal just a voltage? I cant remember. One thing, though, 8.5 volts is a bit low under crank. You might want to consider a new battery. Granted the voltage will drop a bit but getting around 8 makes for hard starts.

Grumpy

What kind of voltage are you seeing at the battery during crank?. Some codes basically shut down at 9 volts. You need a good 200 RPM, at like 10.5v for a consistant clean, good start.
Do you normally have to pump the gas a couple times to start the car with the carb?.

And this is beginning to sound like I deal I just ran into where the ignition module was bad, and during crank, under 400 RPM there was no spark (or refence pulses), but the instant the engine hit 400 RPM and the EST went active then the engine would run. It was only with Lockers and data logging a start-up that I caught there was no cranking DRPs until 400 RPM. And then for grins wound up with 2 modules that did the same thing. But with enough cranking the engine would hit 400 and then start. You might check to see if you have an intial spark, when first spinning the engine over.

Pablo

iTrader: (1)

I havent checked the voltage at the battery but I suspect my lower than average voltage has to do with the fact the battery is in the trunk and has alot of wire to travel through.

I cant really give you a good answer on the carb because it doesnt have a choke so startup is hit and miss. It will fire right up without pumping it (depending on temp) but i have to give it some gas to keep it idling once it fires.

I am pretty sure the spark is good, to keep it cranking i have just been disconnecting the secondary coil wire from the dist cap and i have to isolate it or i get one hell of a spark underhood while cranking, Ill check it anyways with a timing light to be absolutely sure though. It would seem to me that a problem like this would affect the spark too.


I also replaced the module and i tested the pickup coil, pickup coil was good and the module didnt do anything.


Im gonna have to pick up that noid light

thanks
Pablo

JP84Z430HP

Sorry, but close (or pretty sure) only counts in hand grenades and horse shoes.

Seriously, grab a spark tester and noid light. Should be less then $20. If you have enough spark to jump the gap in a spark tester, you have enough to start it. If you get a noid light, the injector should fire (unless it's bad)

In my day to day life of a driveability tech, the most important thing to remember is to make sure you have enough voltage. When diagnosing a no-start, or any driveability problem, the first thing we do is grab a scan tool, look at battery voltage, then look at all the other info on the tool. From there, start the engine (If it will!) then look at charging volts, then continue on to all the other stuff. As a rule for stock applications, anything less than 10.5 volts is not good enough, and I would think that in our higher performance vehicles we would be more critical!

I really think you're having problems due to the low voltage. At the very least, even if that is not you problem, I would do something to get that voltage higher to keep from having other issues.

You may also want to do a voltage drop from the battery to the injector connector with it running (would take some really long test leads!)

One more note, based on an experience from this week:
Check your grounds!
I had a 2000 S-10 land in my bay this week. the thing just didn't pull at higher RPM's like it should. Fuel pump was on it's way out, proved it with a lab scope (very cool way to check a fuel pump, if you've never seen it!). Replaced pump module (about $300 shop's cost, plus labor!) and started to go for a drive. The thing died twice on the way out of the driveway. Got it back into the shop, and I noticed that every time I hit the brakes, the sound of the pump would change (slowed down). I accidentally found that the turn signals would also, which helped in the diagnosis. I pulled the connector off the pump (hard to get to, but not impossible) and checke the resistance to ground. It was like .1 ohms, which is pretty good. Fromw there, I dug through some wiring diagrams and finally found the fix. It seem the truck had been in a body shop, and they had connected 2 of the 3 ground wires from the battery to the body, when 1 of them should have been to the frame, where the fuel pump and rear lights get their groud.

I know this is a long story to reinforce a point, but I hope it will help someone, sopmtime!!!

Pablo

iTrader: (1)

you might be right JP,

I will be going over the car with a fine toothed comb tomorrow, I really want to have TBI track times before I head to japan for the rest of the year. Not many muscle cars there