48jeep

I have added a 91 tbi setup to a 82 camaro 305. when a try to start the car I it just turns over and it appears as the engine never gets primed. I have wired my fuel pump strait to the battery and reprogrammed the chip(removed the VATS). if I add a little fuel(prime the engine manually) it will start and run. Thinking it might be the reprogramed ECM I bought a 7747, and still have the same problem. I know the ECm is suppost to turn on the fuel pump for 2 seconds, when should the ecm prime the engine and how does it know when to do it.

Thanks Ed

RBob

iTrader: (1)

There isn't any real priming of the engine via the injectors. During cranking the commanded AFR is lowered to add additional fuel. Couple of items to check for hard starting: fuel pump pressure needs to be between 9 and 13 psi (low pressure == hard starting). Coolant temperature sensor (CTS) reading wrong, and check that the TPS isn't wired backwards. Center wire measured to engine block should be around .5 volts with the throttle closed.

RBob.

48jeep

Thanks for that info. What does the crank signal do? witch lead does it connected to on the starter?

RBob

iTrader: (1)

Crank signal is used by the ECM for the fuel pump relay malfunction diagnostics. Goes the 'hot during crank' terminal on the solenoid.

RBob.

48jeep

Checked my sensors and they seem to be fine. Fuel pressure is good @12 psi. My injectors never seem to squrit fuel except for a very quick pulse when I stop cranking the engine. Some post suggest the ESC module can inhibet the injectors while starting, is this true. I will have mine tested, does this mean the ECM uses the ESC and distributor to know that the engine is spinning?

That last last question sounded like I might be stupid. What I'm really trying to find out is why my injectors are never adding fuel to my engine during cranking? I know an engine needs three things to run Spark, compression and fuel. When should the injectors start adding fuel when starting and/or what conditions must be met for this to happen? Again if I manually prime the engine it starts and then the tbi works as advertised.

Ed

RBob

iTrader: (1)

Ahhh, BTDT, lots of fun. Either the ignition coil + feed, or the injector + feed, or the ECM IGN+ feed is not hot during cranking. Not all circuits are hot during cranking. Some are only hot when the ignition switch is in the run mode, then turn off during cranking.

Note that the ESC module is for knock detection and reporting. Can run without it. The ignition module is in the distributor and is part of the EST system.

RBob.

CamaroRider

Everything apparently works correctly during the RUN phase but not everything works correctly during the CRANK phase.

I guess you are asking:

''What are the differences between the CRANK and RUN phases as far as electrical circuits firing the fuel injectors ?''

I do not have a problem right now but I have interest in the same answer.

48jeep

RBob you were right. while my ignition is in start my injectors were not getting power. I simple rewire and I'm up and running.

On a separate note - My 8746 ECM doesn't not run my fuel pump when power on. I have a 7747 ECM, when I plugged it in it ran the fuel pump at turn on. both ECM seemed to work fine besides the fuel pump running at startup, any sugestions. I have added a new prom to the 8746. if I have to go with the 7747(it is programed for a 5.7) can I just add a new prom with a 5.0 program?

RBob

iTrader: (1)

The fuel pump problem is an easy fix. There is a small transistor in the ECM that pops on a regular basis. Real easy to do as it supplies power, so even a quick short to ground and the transistor is bad.

Open the cover and right near the harness connectors, opposite side of the heat sinks are two small transistors. This is in the corner of the board. The larger of the two is the one to replace. Can use a 2N2907 (small metal can transistor, PNP). Goes back in the same lead orientation as the original.

IIRC I've posted a picture of these here on this board or the DIY_PROM board.

For the '7747, yes, using a 5.0l PROM will work for your setup. Many trucks used the L03 with the '7747. Although, the '8746 with a Camaro PROM in it would be the better setup.

Although, is the 305 motor stock for an '82? The L03 engines used swirl port heads which don't require as much spark timing. So using a calibration for those heads you will lose power and mileage with a L03 tune.

Good to hear it's running.

RBob.

48jeep

I am a electronics/computer tech in the Air Force, and will attemp to repair the 8746. The 305 has the stock heads with a mild edlebrook cam. Now that I have the engine starting, I'm going to start to learn how to tune the ecm to my engine, I have a burn 1 and this site has some great forums.

Thanks again,
Ed

latinpro771

hey what did u do 2 fix it cause i have the same problem. and where can i find that pic at of the ecm

RBob

iTrader: (1)

https://www.thirdgen.org/forums/dfi-...hlight=picture

RBob.

48jeep

I just wanted to confirm this did work for my ecm. Although you say to purchase a metal cap transistor, I ask why a metal one? my ecm had a non-metal one to start. the metal one was only a dollar (and the non-metal 50 cents) and I can afford that but, does it matter?

On another note: where should I mount a knock sensor on my 82 block? does it matter if I have a pvc valve on one, both , neither?

Ed

RFmaster

In the old days when everything was discrete metal can transistors were used in extended temperature environments - mil spec temperature ranges or extended industrial. It was not unusual to test an electronic assembly from -50C to about 95C or even higher. I did not know any better at the time.
Transistor metal can provides hermetic seal and additional thermal path - generally found in high rel JAN, JANTX spec'd parts.

FWIW in car operating environment is on a par with some worst extended industrial spec!


//RF

RFmaster

Knock sensor should be mounted instead of one of the two drain plugs - just above oil pan rail. Prepare a pan to catch antifreeze since this is the lowest pint of the coolant inside block! Also, Drain plugs are known to break off! Get easy-out and drill handy, just in case. Removing header or exhaust manifold aids ease of operation.

PVC valve is mounted through a valve cover - wrong place for KS (One is enough)!

//RF