back with new problem on 90 camaro 3.1 v-6

[cocobolo95]

Have a fuel related problem with my 1990 camaro 3.1 v-6 auto trans car. Drove car to library last Monday. Came out and engine would start & run for about 4 seconds then die. Would repeat this behavior on repeated start attempts.

First thought was security system failure. But when key turned on security light cycles on then off like it should. Used scanner and security checks out with it also.

Ignition system is fine. Good spark. Pulled fuel rail, attached spare distributor which I hand turned with ignition on. All fuel injectors spray with a good spray pattern when dist is turned. Fuel pump also runs for key on prime and when dist is turned. Fuel pressure at key on prime is 43 psi.

Can run engine if I spray gas into throttle body. With scanner hooked up in data mode, all sensor readings are within normal limits except injector pulse width. Normal pulse wdith at idle usually runs about 1.7 to 1.9 . With engine not wanting to run unless gas sprayed into tb, pulse width is running at 1.1 to 1.2 .

Here's the crazy thing. Last Thursday, I came out started car and it ran normally, including inj pulse widths running in the normal 1.7 to 1.9 range at idle. Had not done anything to engine to account for this change. Engine ran and car drove fine.

Went out the next morning, started engine and it was back to dying after 4 seconds run time.

I've installed new spark plugs, swapped in known good iac, 2 other ecm, with no change. Checked power supply wires and ground wires and all is good. Engine still starts and runs for 4 seconds and dies.

I need some ideas on where to take my investigation next.

[1320_john]

What is the fuel pressure doing? Is the pump priming with key switched to on and the car is running on that initial prime? With many GM vehicles, the fuel pump runs off the oil pressure switch. When the key is first turned on, it primes the pump while the motor has zero oil pressure, then relies on the oil pressure switch to continue to run the fuel pump while there is oil pressure. My guess about the pulse width being so low might be that the pulse width is calculated from RPM and since it isn't running the RPM is lower than idle. Good luck! Let us know how it turns out!

[cocobolo95]

Fuel pressure is 43 psi @ key on prime. And when idling it is 36 psi, just as it should be. There's no problem with fuel pump running when engine is running. It's just that pulse width of injectors are too low to keep engine running without spraying gas into tb. I have the carpet rolled back from gas tank area, trap door for pump area is removed. I can actually hear the pump running with engine running.

[cocobolo95]

Have a question. Are the injector drivers in this ecm part of a quad driver circuit? And if yes, what other components are on this quad driver?

The injectors of 1990 camaro 3.1 are batch fire with 2 circuits, 1 for each side of engine.

[1320_john]

Is it possible to get a datalog of the car starting up and running, then a datalog of the car trying to start? Are the injectors batch fire on that engine? Maybe putting a scope probe on the ECM side of the injectors to make sure they have full voltage swing? Does the car have VATS?

[cocobolo95]

My scan tool reads sensor data but does not save it. I have read data when car is running normally. Have read data when assistant sprayed gas into tb. Big difference is pulse width of injectors. When normal pulse width is 1.7- 1.9 @ idle. When you open the throttle pulse width increases.

When car starts, runs, dies, pulse width is 1.1- 1.2 @ idle and stays there when throttle is opened. Injectors are batch fire.

Car has vats. It cycles normally when key turned to on. And scan tool reads vats as being good.

I asked in post # 4, if injector drivers were part of a quad driver circuit in ecm. And what other drivers share the same circuit.

Have scoped the injectors and wave form doesn't change when car is in start, run die period.

As stated in original post, last thursday, came out car started & ran normally. Drove car, off and on, all that day. Data on scan tool was normal. Went out the next morning and car did start, run, die again.

Car starts easily. One chug of starter and car runs. This is both when normal and problem occurs.

[steveo]

if it was a quad driver issue; you wouldn't have a predictable failure mode like 'starts for 4 seconds then dies'.

just a theory, but it's on prime cycle (for initial startup) in a primitive fueling mode based just on temperature/tps/rpm, then dies when it switches to speed density or maf or whatever. does it even have a maf? i don't know much about the 3.1...

[cocobolo95]

Engine has no maf, runs speed density, and uses batch fire injector strategy.

[RobertISaar]

with the MPFI 60V6 code, unless you disable a certain flag, idle and coastdown fueling is actually done more like a hybrid alpha-n calculation. TPS and IAC are absolutely critical to proper operation in this mode. I would take a look at those two items to make sure they're operating properly.

[cocobolo95]

Tps is functioning correctly, I will take a look at readings new iac gives. But when I have an assistant spraying gas in tb to keep running, if I press throttle down, fuel injectors still don't increase pulse width. I've had engine up to 3500 rpm in park by increasing the sprayed gas amount.

As stated in earlier post, last thursday car ran fine all day. Injector pulse widths were back to normal # idle and increased as throttle was opened. Next day car again started, ran, died.

[RobertISaar]

you have an intermittently bad sensor. opening the throttle should have increased pulsewidth through more than one function(higher MAP/higher TPS, both of which should have been read as a large increase in airflow and require more injector on-time to keep the desired air/fuel ratio.

[cocobolo95]

When my assistant sprays gas in tb, and I open throttle, tps gives smooth change in open %, map reading change with change in throttle position also. What doesn't change is injector pulse width. And 3 different ecm's show same symptoms.

Checked iac counts, around 30 at idle, increasing a little as throttle opens then drops down in counts when throttle opens wider. Goes back up in counts when throttle closes.

[cocobolo95]

Decided to check my injectors again. Last time all 6 had great spray patterns, didn't leak when closed. This time I had 2 that dribbled when closed, 1 that wouldn't close and sprayed all the time, and 1 that wouldn't spray at all, wtf. Here goes another $300 for parts that I'm 95% convinced won't solve the original problem.

Going to try cleaning my 25 year old oem injectors. Have an ultrasonic cleaner that I will use. After cleaned or new injectors installed and car still won't stay running, will start tearing the wiring out looking for opens & shorts.

Any member have a set of new 15lb injectors for sale at a reasonable price?

[CFI Z51]

I had similar problem with a subaru years back, would run for 5 sec then die ,instant restart ,5 sec die...
the short story ; after 5 sec voltage source (for what i don't know) changed from batt to alternator, which was toast.
Just something to check off the list.
Nice test with the spare dizzy , I'll have to remember that one.

[cocobolo95]

System voltage shows normal reading at gauge and scanner. I thought about alt putting such a heavy load on engine and making it die. So I unplugged alt, car still died. Removed drive belt also to see if power steering was killing engine. Won't run more than 4 seconds with accessory drive belt off.

Good suggestion, however. Keep those ideas flowing.

[cocobolo95]

Am currently cleaning my fuel injectors. Soaking the bottom part of injectors in my special blend injector cleaner. Will soak for a week. The first soaking changed the clear fluid to a orange brown color so they must have been pretty gunked up. The 2nd soaking, the fluid has a light orange/brown tint to it, so injectors are still dirty.

Will change fluid 1 more time and soak 2 more days. Then I'll put them in the ultrasonic cleaning machine for a final cleaning. Will power up the injectors during the final cleaning using an ac power source. That way injector will open & close 60 times a second. This will help break up any last bits of varnish built up. Will back flush while in last cleaning cycle.

[RobertISaar]

as long as your AC supply doesn't exceed about 15 or 16 volts peak, you should be fine(or is just current limited to about an amp). above that and you start risking damage to the injector coils.

I think ideally, you would want to drive them with a square wave to build/hold the magnetic field fast, seems like it would be more likely to break free anything that might be holding onto the pintle.

[cocobolo95]

Voltage runs just under 12 volts when hooked to injector. If I would have had a square wave source at hand, I would have used it. But I used what I had.

Hit one injector with the ultrasonic machine, while powering up the injector and back flushing with a mity vac brake bleeder. The discolored stuff just poured out of injector. I'm hoping to get some more life out of the 25 year old parts.

But still 95% that clean injectors won't solve my original problem. But hope is still there. I'm betting on the 5%.

[billygraves]

In this era the injectors shorted out internally. Methanol, Ethanol and MTBE eroded the internal injector wiring coating. Have seen where the splice for the injectors within the harness had a highly corroded splice. The splice connects the two injector drive wires together. Try to temp 2 wire a jumper from the car injector harness to the ECM injector driver.
If it has a distributor, the base will corrode and do some very odd things. Remove it and insure it's clean. Test the strength of the magnet and if the pick-up coil connector is slimy or corroded ar sticky, replace it. Regrease the module with silicone grease. Install a new dist o-ring or oil will leak.

[cocobolo95]

Car has brand new distributor. Checked it out and everything in dist is top notch. Old dist had cracked magnet.

Thing about the dist in relation to injectors. If I pull dist out and turn by hand, the injectors will fire for as long as I turn dist shaft. Same with ignition coil wire off and engine cranked. Injectors will fire for as long as engine cranks.

It's only when engine actually runs that it goes for about 4 seconds and dies. I can do this all day long also. Start-run-die.

I will try rewiring the injector wires to ecm and power supply and see if that makes a difference. This is if cleaning injectors makes no difference. I've ohm ed the injectors and all is well there. Will check again to see if resistance changes after injectors have been pulsing for a while.

Keep the ideas coming.

[billygraves]

You say "All is ok there" with the resistance of the injectors. What was the ohm reading at what temp was this done?
All is OK with the distributor? What does this mean? Does the magnet on the shaft have a strong pull when the poles line up? What does the block look like, was it cleaned? It has a bearing on the Reference out to the ECM signal if the base or grd is corroded. Ask a shop in the rust belt.

You can try this: I use niod lites for the injectors because this will fill up the cylinders very fast. I place a ST-125 spark tester on the secondary coil wire to take the spark load instead of having the spark go to unknown cyl inside the cap
Using a Weller 550 soldering gun, get it close the the dist pick-up coil and pull the trigger on the soldering gun. This pulses the pick-up coil at 60 hz. You can calculate your 6 cyl RPM it well simulate. It is easier to test electrical items this way rather than run down the road til it fails. Wiggle wiring, connectors or spary H2O on wires to test for failures.

[cocobolo95]

I have the 90 Camaro factory service manual to get my specs from. It was about 80 degrees when I tested the injectors. They all ohmed within factory specs. I tested the pickup coil for dist using ac volts on multimeter. Turned dist shaft, voltage was within specs even with shaft turning slowly.

When I say I disabled ignition system, what I did was swap coil wire for a longer one and use my st-125 on the coil wire. This way it was a long way from the gas being sprayed when my fuel rail was out of engine being tested. There are no ignition problems as my engine will run as long as gas is being sprayed into throttle body. This is when engine is put back together for testing. I can open the throttle and rev the engine to 4000 rpm, as long as amount of gas sprayed matches engine speed.

While my assistant is spraying gas into tb, I have wiggled & pulled on wires to see if engine would run without spraying gas. But every time the gas spay quits, so does my engine.

And I've read the data from sensors & actuators while engine was being run with gas. The only readings that were off, besides fuel trims, were the injector pulse widths which stayed around 1.2 - 1.3 no matter how fast engine was turning. So the problem seems to be the ecm not commanding the fuel injection pulse width long enough to run engine.

My normal pulse width at idle runs 1.7- 1.9 with increasing pulse width as throttle opens up.

[cocobolo95]

Finally had some real progress today. Decided to test the 30 hertz fuel enable signal again. Last time I tested it was good. This time signal started out at 30 hertz then went crazy. Anywhere from 20 to over 100 hertz. Think I've found the smoking gun.

I am going to order a 30 hertz bypass module from baker electronix. For those with problems with newer models, they make a 50 hertz module also.

[JP86SS]

Do you mean the VATS signal?
It can be anything from 33-66 Hz IIRC.

You can change the min and max parameter in some of the bins.

[cocobolo95]

It's always been right around 30 hz but I"m getting a signal now that is unstable and going way higher hz. Changing the bin file would be a good idea, but I'm not set up to burn chips. That's why the 30hz bypass module. I could buy a new tdm, but they start at about $240. Too much.

An used one would make me find which of the 15 key resistances it's programed to. And being as old as the one in my car, I have serious doubts about how long it would last.

If I did burn a chip, I'd just eliminate security altogether. Don't believe thieves are hanging out waiting to steal my 25 yr old 3.1 v-6 bomb.