No Injector Pulse

[Project96]

I have a fresh built 1994 TA LT1 M6 that has been a long project for me. I bought the car with a bad engine & swapped in one that I built/had built. I have a new opti with spark at all the plugs. I have bypassed the VATS system with the resistor method. I have power to all my injectors. The security light comes on & goes off after a few seconds of the key being on. I have fuel pressure (44 PSI). I want to hear this thing run before I pull my hair out. I went throught this weekend & about pulled my engine harness out just making sure everything was hooked up. The only things not hooked up are the EGR (deleated), air pump (deleated), & the A/C (deleated). The engine has a CC305 cam installed & P&P heads with 0.020 over pistins. I know I need a tune but I should still be able to start it. There is 1 very small grey wire by the PCM that I am not sure where it goes, if anywhere. I know the PCM gives the injectors the ground to turn on, but what tells the PCM its time to fire them & I will start checking there. Where does the PCM gets its ground from? Thanks in advance for any help.

[Project96]

I figured out where the PCM gets its ground from. Is is bolted to the bottom of the oil pan next to the passenger side motor mount. Any ideas???

[Alex94TAGT]

Few thoughts:

1) Don't forget the little things: Check your injector fuses in the underhood fuse box. As you said, the injectors are always supplied +12 VDC, but the PCM decides when to ground them out. Check for power on every fuel injector's electrical connector (might need someone to crank over the engine while you test -- don't remember if they get power at all times or only while cranking/running).

2) Not saying this is what's going on in your car, but I had a similar problem that had me puzzled for weeks. I had spark, but the fuel injectors just sat there doing nothing. The problem ended up being a bad pin in the Optispark electrical harness connector along the passenger-side intake manifold. Can't remember if it was the low- or high-resolution signal's pin that was bad, but the Optispark's signals are used by the PCM to fire the injectors. Weird thing is that it didn't ever throw a diagnostic trouble code -- I'm still not sure why it didn't. And I had spark, which threw me off the trail. Once I fixed that connector, it started right up.

Sooo, I'd set your multimeter to continuity check and test the Optispark wiring from the Optispark all the way to the PCM pinouts. If you don't have it already, I'm pretty sure Rob/Shoebox has the PCM pinout files on his website -- or I could look the pins up for you. You can also use that to verify the PCM grounds are getting grounded, as well as to test the wiring from the fuel injectors to the PCM.

3) Wouldn't rule out the possibility of a buggy Optispark. Wouldn't be my first assumption, but you never know. Something has to be causing the problem.

4) The loose gray wire by the PCM, if you're referring to the one near the passenger hood strut with a plastic connector on the end, is most likely the fuel pump prime connector. With the car off, you can kick on the fuel pump by supplying +12 VDC to that wire.

[KLaBZ28]

I figured out where the PCM gets its ground from. Is is bolted to the bottom of the oil pan next to the passenger side motor mount. Any ideas???

I had the same problem with my A4 95 Camaro. I had fuel pressure, injectors were getting no pulse. I buzzed out all the wires from the PCM and the opti; the opti was sending the optical signal to the PCM but the PCM wasnt sending it out to the injectors(???). I know the VATS can disable the injector pulse but mine was ok. All grounds good. I ended up getting a spare 94 PCM from the junkyard and swapped it in to try fired right up. Car is bolt on only AIR EGR delete and flashed a tune a couple times with my laptop or tuner cats. I'm think either A. something damaged the PCM during flashing so many times or B. when it bounced off the limiter tuning my shift points it did something. Just my thought if you have a spare pcm around or can get your hands on one I'd try that. I still have to diagnose the 95 pcm and see what really went wrong.

Good luck :)

[firebird_1995]

another thing to try is unplugging the MAF sensor and see if it will start.

[Project96]

I just got back from ATL this evening & will be doing some more trouble shooting this weekend. The injecors have power all the time when the key is on so I know the fuses are good. I have tired unplugging the MAF to no avail. I will be checking the pin out & the opti connection this weekend as well. So Alex94TAGT, if you have that pinout handy I would really appreciate it. If not its cool I can find it on shoes site. I have used his site for other checks as well. Just been bugging me for a while & had to take a break & rethink my approach. Thanks for leading me in another route to check. I will keep you updated.

[joelster]

If you spray a little starter fluid it will fire right up since it has spark. It may even keep running too. My friend had an IROC that would never start when it was cold. He would spray starter fluid and it would start right up, and it would restart if it was hot. It ended up being the injectors were at fault.

[Project96]

I have a spare whole top end, intake, heads, fuel rail, throttle body & injectors. If I need to swap the injectors I will. I just need to get the PCM to send the ground signal first. Didn't know the grey wire was the fuel pump prime. Learn something new everyday!!!

[Alex94TAGT]

So Alex94TAGT, if you have that pinout handy I would really appreciate it.

Sure. You'll have to pull the "Black" PCM connector.

1. Optispark Red/Black wire --> Pin 2 on PCM black connector
2. Optispark Pink/Black wire (Mine actually looks Orange/Black from fading) --> Pin 3 on PCM
3. Optispark solid Red wire --> Pin 14 on PCM
4. Optispark Purple/White wire --> Pin 20 on PCM

[Project96]

The car is at a guys house getting looked at. We are going to swap some labor. I worked on his 4wheeler & he is going to look at my car. Hopefully it will be figured out soon so I can get this thing on the road.

I want to get a program to tune & edit the PCM in the car. Is there a specific one that you guys recommend? I have been looking into tunercat but not sure which one to get. There are 2 kits available. The LT1 tuning kit & the LT1 pro tuning kit. Is the pro tuning kit worth the extra $100, or is the reg kit ok?

[Alex94TAGT]

The car is at a guys house getting looked at. We are going to swap some labor. I worked on his 4wheeler & he is going to look at my car. Hopefully it will be figured out soon so I can get this thing on the road.

I want to get a program to tune & edit the PCM in the car. Is there a specific one that you guys recommend? I have been looking into tunercat but not sure which one to get. There are 2 kits available. The LT1 tuning kit & the LT1 pro tuning kit. Is the pro tuning kit worth the extra $100, or is the reg kit ok?

The "regular" kit provides tuning software/hardware, but you'll be tuning blind. Need some form of feedback to work with -- whether it be datalogging the stock PCM, aftermarket wideband O2 sensor readings, EGT/pyrometers, etc.

The only difference is that the "Pro" kit includes Datamaster -- a datalogging program to record all engine parameters. Very useful program. You can technically download Datamaster for free and run it for 20 free trial sessions before having to purchase. I'm a little rusty on what else is available -- there is also Freescan LT1, but I don't recall if it has datalogging capabilities (never used it myself) -- might only report live/instantaneous sensor readings.

At any rate, there doesn't appear to be any big pressure to buy. Tunercat charges $100 for the Datamaster program separately, so you could buy the regular kit, try the Datamaster free trial, then purchase Datamaster at a later date if you so choose. It's effectively the same price in the end.

[Project96]

Thanks for the reply. I was wantin to get a wide band as well if funds ever come up. I'll go ahead & get the "regular" kit & download the trial version of datamaster. That might put a few bucks toward something else for now.

[blazing blazer]

hi im new to posting on forms, and i have a 94 lt1 i pulled from a camaro and i put in to a 98 blazer. i got it just about done but now it wont start. i got good spark and fuel press but no inj pulse. im going nut

[Tyler Wheat]

Do you have a VATS bypass wired in? Does the car start at all?

[blazing blazer]

It cranks, I got good spark good fuel press but the pcm is just not firing the inj. If it was the vats it would start for about 3sec and shut down. I call a shop that works on these motors a lot and they said if one or more inj short out it will shut them down or my pcm is bad.

[Tyler Wheat]

Yeah, sounds like bigger problems than the VATS.

[Project96]

I should have updated this a while back. The reason the car had no injector pulse is because the 4 pin plug on the passenger side of the intake manifold was broken when I got the car. I had the pins in the wrong location. Once they were installed in the correct location the injectors had the proper pulse. However, upon trying to start the car it shot a flame out the TB about a foot long. WOW!!! Out of time… I had to pull the timing cover off & check the timing. The cam timing was correct, but the pin that drives the dizzy was about 180* out. I had to remove the cam gear & drive the pin out from behind. Once I cleaned the splines up the pin went into the cam gear like it was suppose to. I guess that’s what I get for having the damn machine shop assemble the bottom end for me. Once it was finally put back together...it ROARED to life. WOOOHOOO!!! IT’S ALIVE!!! Granted it has an exhaust leak & its only running on 7 cylinders, but it is definite progress. I have been waiting for that moment for so long. Now I can start messing with it a bit more as my enthusiasm has been rejuvenated. I don’t think I will be able to drive it to the shootout as planned as $$$ is pretty tight for me right now & it still needs some work before its ready to drive. Hope this helps anybody. As for the Blazer, I would start by checking that all the pin locations are correct to the ECM. Do you have power to the injectors? Make sure that all the grounds are good, not just the one from the battery to the block.

[blazing blazer]

All grounds are good. And I have power to the inj. And plus ill my wiring is brand new by current performance, this guys are awesome!! I don't think it would be the wiring but I will look it over. If its not the wiring would you have any other ideas? I just want my beast to come alive!

[blazing blazer]

I got it!!!! All this time it was just a tps. It was telling the pcm 100% I replaced it and she fired right up!!

[Fastbird]

I got it!!!! All this time it was just a tps. It was telling the pcm 100% I replaced it and she fired right up!!

Flood mode. That would do it. Nice job finding that.

Posted from my Rooted and ICS'd Rezound

[The SRZ]

Nice find! Glad it was something small for you.

[blazing blazer]

Got to love the dumb things. Thanks for the help guys.:)