Leo101010101

Hi everyone so i have an 89 rs with a 305 tbi, stock tbi and stock injectors. the car starting running rough and then stopped starting all together. i narrowed the problem down to the injectors not getting a signal to spray fuel.

things ive tried: new ecm (same prom), new pick-up coil, new ignition control module,


also the engine will start and run on starting fluid

monkihead

How did you check for signal?

Leo101010101

used a noid light

i also tested every wire involved for continuity and made sure i have power going to the ecm. both checked out ok

Leo101010101

someone also told me it could be a faulty sensor telling the ecm to cut off fuel. what sensors would do this?

ASE doc

The oil pressure fuel cutoff switch shuts down the fuel pump, not the injectors. Stupid question but are you sure you have power? The ECM controls injectors using a quad driver which turns the injector on by grounding the low side. There should be 12v at the high side with key on. Also, the system could be in flood clear. When TPS voltage goes over 80% whlie cranking, the ECM shuts down the injectors to clear fuel from a flooded engine. Check tps voltage. Should range from .5 at closed throttle to 4.5 at WOT. Hope this helps.

Leo101010101

with key on there is constantly 12v going to one prong on each injector, the other wire has no power.
ok ill check the tps thank you

ASE doc

Also, if TPS checks okay, use a test light and look for injector pulse at the ECM connector while having a helper chank the engine. Its good you checked power to the ECM, also good to check all grounds and signals such as PIP(primary ignition pulse) from the ignition module and TPS voltage at the ECM connector. You can do this by carefully back probing the terminals. Double check connector terminals for tension.

dawb

I just had to do a distributor in my 305 tbi a week after doing a solid tuneup. I never did test the injectors for power, but since I have a truck, I could get at the connector for the fuel pump. Checked that I had power with a simple test light @ 'ON' (I did, and could hear the pump) but on 'CRANK' had no power to the pump... If the ECM doesn't get a solid ignition spark signal, it won't send signal to the fuel pump... so POSSIBLY, it might not send signal to the injectors either at that time? I didn't check into it, as I had a spare disty and threw it in... fixed er right up. This was only last week. It may not necessarily just be the ignition control module, and could be the disty itself. Mine was pretty corroded (didn't even notice when I changed cap/rotor lol).

Just something else to check...

Leo101010101

just to add.
the engine will start right up and run beautifully on starting fluid and im assuming it will run all day if i keep standing there and spraying more and more into the throttle body

ASE doc

Hey Leo, Are you still having issues? no word from you in a while. If its fixed, let us know what did it.

Leo101010101

still issues, ive tried whats been said on this thread but no luck so far. havent had time for this in a while bc another project fell on my lap but ill let you know.

ASE doc

When you get a chance, double check ECM grounds as these are needed for the ECM to ground the low side of the injector. Also, check injector impedance. Each injector should test at 12-17 ohms with an ohmmeter. Testing TPI injectors can be a bear. One way to do it without pulling the plenum is to test at the ECM connector. Identify the injector circuits(D15 & D16) then, with the ECM disconnected, Test between D15 and injector fuse 1, then between D16 and injector fuse 2. Impedance will be single injector impedance/4. Or about 3-4.5.

Leo101010101

thank you for the advice

ASE doc

I just caught on to something in your original post. You say you have 12v on one side of each injector. You should have 12v on both sides of each injector. The ECMs pulls the low side to ground to fire the injector. When the low side is open, as in when the injector is not actually firing, you should see 12v on each side of the coil.

You may need to look at the strength of your 12v supply. Try testing the injector circuits by quickly grounding the low side of each injector. The injectors should of course click.

Also in post #12, I was mistaken and thinking you had TPI. Your TBI injectors are low impedance(about 1-2 ohms each). They still have two seperate drivers but each driver just controls one injector.

Napster134

Ever find the problem to this? Having the same issue... somewhat... lol

Keoman

iTrader: (3)

Any luck Leo?
After rebuilding my engine I am having the same problem. Runs like a charm if you stand there all day and squirt starter fluid in the Pleum. I have not check the Voltage on the injectors yet as I am not at home at the moment. I have TPI however.

gregv92c

any answers yet ? I just went to start my 89 RS and if shut off and won't start ! Will fire with starting fluid but that's it !
Thanks

Napster134

Check all grounds and concentrate on checking the grounds at the rear of the engine (Normally bolted to the back of the passenger and drivers side heads)

Also check the INJ1 & INJ2 fuses (tbi) But im sure TPI probably has injector fuses as well? maybe...?

I know that some of the ignition system sensors and modules are related to the injector's pulse.

I would say that the main ones are the pickup coil and ICM. But maybe the ESC could be related as well.

gregv92c

So are you saying a new distributor fixed your problem ???
Thanks

swabhammer143

iTrader: (1)

I'm having this same issue. Did you ever solve it?

Schurkey

IF (big IF) the vehicle is wired like my 92 and 93 Luminas, and like my '88 K1500, the oil pressure switch CAN NOT shut down the fuel pump.

It can keep the pump RUNNING if the fuel pump relay fails. It can not STOP the fuel pump if the pump relay is still providing power.

roryamacnish

Same issue, 89 305 tbi. No pulse when cranking but when I spray starting fluid, starts right up and idles fine. Injectors work fine after start which leads me to believe voltage and impedance is fine. Any ideas on why they won't prime for crank but will pulse for idle? Also car will start again if I attempt again within 10 mins as long as motor is warm.

RFmaster

Check your ignition voltage supply at ECM during cranking - you may have a bad ignition lock cylinder. Distributor is getting power since engine is able to fire once your spray some fuel. Check voltage during cranking at ECM interface connector pin A6 - 11.5 to 12v should be present.

//RF

Schurkey

Does the fuel pump relay engage when you turn the key from "Off" to "Run"?

If the fuel pump relay doesn't engage properly, there'll be no fuel pressure until the engine has been cranked long enough to build oil pressure, then the fuel pump runs off the oil pressure switch. Depending on engine condition, you could crank it quite awhile before the oil pressure built up enough to trigger the oil pressure switch to supply power to the fuel pump.

roryamacnish

When I turn key to "on" fuel pump kicks on and stays on which I thought was due to a bad oil pressure switch (don't know if relevant to relay). Will check fp relay tomorrow. Also want to check crank voltage at ECM interface but am not sure how to access interface itself. Want to get you guys some data!

roryamacnish

Okay did a little looking around and went to check fuel pump relay AND THERE WASN'T ONE! There wasn't even a harness just the loose wires hanging around. The tan/white which feeds pump was tied to another wire nearby which explains why the pump was running non stop. Pulled it off of the other wire and tried to start but oil pressure switch didn't feed pump even after oil pressure was well over 6 psi. Sign of bad OP Switch? Anyway pulled fuel pump relay harness off of my other Camaro and ordered another relay which should come tomorrow. If OP switch turns out to be shot but replacement relay works should I even bother replacing OP switch?

Schurkey

Fix it RIGHT. Clearly the last person to work on that system didn't bother.

Six_Shooter

iTrader: (2)

On a TBI, if the injector is unplugged to check for voltage, only one side will show voltage, since the other wire is only connected to the ECM, and no other injector. It's only because there are usually other injectors connected, like an MPFI set-up where voltage is seen on both sides of the injector, when checking for voltage.

Have you tried simply unplugging the TPS and starting it?

In one conversion I did many years ago, I somehow missed hooking up the ground for the TPS sensor, so the ECM thought the throttle was being held open, and put it into a "clear flood mode". Discovered this, and unplugged the TPS, it fired up right away.

Juve88GTA

Any luck finding the problem?
I'm having the same issue. My car only starts with starting fluid, Fuel pump is new, 40psi of fuel at shredder valve, I tested the injectors and they're at 18 ohms, connector pulsate when cranking and the injector also tic…

roryamacnish

Sorry Schurkey, definitely owe you and the forum an apology for that one! Best words of wisdom right there. We're on this forum cuz we love these awesome machines and we gotta do right by them. If you know it's wrong and it's within your means to fix it, FIX THE DAMN THING. Btw tried unplugging the tps and starting but injectors still didn't prime during crank until oil pressure got to about 20 psi. Fuel pump was running the whole time too.

goliath88

yeah man, these guys are awesome on here, Schurkey also helped me with my ride recently, along with Tunedperformance.

check out my thread if you need help identifying those wires. i had to replace the connector to the fuel pump relay, and forgot the order of the pinout. they helped out. explained what each wire does.

just curious though, whats your fuel pressure at?

James Hart

Similar problem on my 91 rs,
305 tbi.. Randomly doesnt start, no spray at crank but usually i walk away for a few minutes and then it fires right up but sometimes it stays dead for a while.
Its been this way for a cpl years and its getting to be frustrating lately.
2 years ago the car sat dead for about a month due to do this same issue.. I replaced the distributor, rotor, ecm, plugs and wires, rebuilt throttle body and almost replaced the injectors but they tested fine. I then found that the wires off the ecm for the vats had been cut and reconnected to bypass the vats, after rewiring the car finally worked again for a while but then started doing the same thing again.
Everyone sais fuel pump but once it starts it runs fine, never bucks or stalls and after 3 yrs of being this way, if the fuel pump was bad it would have failed by now.
After reading this post im wondering if the TPS or oil pressure switch could be the problem.. It does hold good oil pressure though.
I might add that it does seem to run rich and smells likeunburnt gas alot which makes me think its flooding itself out...
So would i most likely be looking at the TPS for it?

Tuned Performance

iTrader: (92)

When it happens check b6 of your ecm. The passkey module should put out 2.5v or 30-50 hz at 50-60%. If you don’t have this signal it’s the passkey module.