tonydee64

This is kind of a long shot, but I thought if anyone would know the answer it would be you guys. I have a 96 TA with a 383 6M, cam, headers, ported heads, ported intake, bbk throttle body..etc.. anyway the other night I'm driving the car and out of nowhere it starts mssing real bad. Backfiring out of the exhaust...almost didn't make it home, smoke everywere, it was bad! Anyway, my ecu threw a MAF code so I replaced it as it has been doing that alot lately (the car will not start with either the new old MAF). I is still getting good spark at the plugs, and the motor shows good compression across all cylinders. The fuel pump is priming ok, but as soon as it stops priming the fuel pressure at the rail drops from 42psi to 0 pretty quickly (I think its always been like that). It's a Walbro 255 in-tank pump. I am not getting any injector pulse, which as I understand it can be caused by lack of oil pressure, a bad tps sensor, or a bad Vats system. My car will crank just fine, and acts like it wants to start, but won't.. it has thrown no codes. I also just installed a brand new AC Delco optispark and it made no difference whatsoever.... and help you guys can offer is much appreciated... DO I have a bad ECU?

LT1-DAN

Fuel regulator?

tonydee64

I was kind of heading down that path, maybe a fuel pump, relay, etc., but I don't think that would cause no injector pulses... Does anyone know where the fuses are for the injectors? although I do have 12 volts going to each injector... I think it might be a oil pressure sensor that is faulty, causing the ecm to not send pulse signals to the injectors. When the car started acting up, the gas pedal basically went dead... I had to gently feather the throttle just to get home...

fast92lt1rs

Injector fuses are in the fuse panel under the hood. I believe they are the 2 brown 7.5A fuses. There is power to all of the injectors at all times. The ECM fires each injector by completing each injectors ground at the propper time. Pull the vacuum line off of the fuel regulator. If there is fuel there then it is leaking inside.

Pete

tonydee64

I only have one fuse underhood labeled "inj". But, it all of my injectors are getting 12 volts, I'm guessing it's not my fuses as they are triggered by the ECU grounding each individually. I have tried to start it by having the new MAF plugged in and unplugged, it made no difference. I also think that if it was a oil pressure issue the motor would start and then die... but I'm not getting any injector pulses whatsoever....

djjab57

iTrader: (17)

x2 I would check the fpr Its sounds like what mine was doing when it went out. When i replaced it i also noticed my fuel rails were dirty It would be a good time to clean them if thats the problem

tonydee64

Would a bad fuel regulator cause the ECM to not send injector pulses? For some reason I am getting no injector pulses. I know that if your motor fails to make at least 4psi of oil pressure you will not get any impulses. If your VAT is faulty you will not get any pulses. My car has an aftermarket pan that does not have provisions for the low oil level sensor, so it's not that. I am getting power to all injectors, so my fuese are not bad. Can anyone else think of a reason why I would not be getting injector pulses? When I hook up my Actron code reader I am able to read the sensor data. I have no idea if this means my ecm is good... My car has been down for about two weeks... It looks like it might be time for a trip to a garage...although I'm not sure to where...

tonydee64

I just went out and tried to use some either to try and start it, no luck. I am getting spark like crazy, but I think it's still my opti. I just bought supposedly a new AC delco from Ebay and I think it might be dead. I am seeing 5 volts from both the low and high res reference wires coming from the ecm. I sounds to me like the motor is definitely trying to start, but won't....

96capricemgr

iTrader: (1)

Try unplugging the MAF and then try and start it. I wonder if it was MAF wiring that was the cause not the MAF itself, and if the MAF is faulty but the pcm does not yet know it then the engine may not get proper fuel.

tonydee64

It doesn't seem to make any difference if the MAF is plugged or unplugged. I just think I bought a bad ahem "new" opti... darn.. I seem to have power in all of the right places... I have heard people say that the vented opti can be installed in three positions. As far as I can tell the dowel from the cam can only engage in the one alongated slot that is "squared" off...

96slow6

Are you getting the 12v to the pink wire going into the maf? If not take a look at your o2 sensors. The maf and the heater for the o2 have the same power supply. If you cook an o2 the maf will die. Usually it wont kill the car completely but its another place to look.

bobdec

Tonydee, You may have a couple of problems, First your fuel pressure should Not go to 0 rapidly after priming. Every time you turn ign key to on position a PCM output signal runs the pump for about 2 seconds (direct wire). It should get the rails pressurized after a couple of those cycles and stay there for at least 10-15 mins. If you are loosing pressure rapidly it could be a bad regulator or leaking injector(s). The check valve in your fuel pump should keep the supply line full of fuel and the regulator keeps the pressure regulated, they should both work together. After engine starts a different signal from the PCM (requires Opti Pulses & 5-10 lb oil pressure) picks the fuel pump relay and that keeps the pump on when the engine is running.
As far as injectors picking check your tach carefully when cranking the engine it should register 100-200 RPM if not suspect the low res Opti signal not getting to the PCM. When you checked the hi & low Opti resolution you saw +5 volts, those lines are pulses not DC voltage the low res should be 8 pulses per camshaft revolution and the high is 360 pulses per cam rev. Try the AC multimeter settings if still at +5 something is weird. Also .. See shbox's web site for checking out the opti... and fuel regulator http://shbox.com/1/4th_gen_tech2.html#opti_test http://shbox.com/1/4th_gen_tech2.htm...essure_testing
Good luck....

tonydee64

Thanks for your reply, yep.. sure thing, I have 12 volts at the red MAF wire. Thanks for your $.02!

tonydee64

Thanks Bobdec, although the check valve in my fuel pump is most likely bad, it is a Walbro 255 and I'm pretty it's been that way for a long time (I remember it being that way when I replaced the last opti). Anyway, I've ohmed the injectors and they all came back at about 146 ohms. My plugs are not wet all with fuel. All of the injectors are receiving 12 volts with the key in the "on" position.

My engine does not have an oil pressure switch that would prohibit the ecm from firing the injectors as the ecm always thinks it is receiving oil pressure (there is actually a pipe plug in the sensor hole).

I'm starting to think that I have a bad ecm.....oif course there's no way to check it. Is there anything else you can think of that would prohibit the injectors from firing? Even if my fuel pump is bad I would still think that the injectors would fire.... The new opti is doing exactly the same thing as the opti I just removed. I can plug the old opti in and (while laying on the intake) and spin it by hand.... you can hear the spark and fuel pump continuing to pump.. I give up..... this one's gotten the best of me...

bobdec

Correct the oil pressure keeps the fuel pump running, nothing to do with picking the injectors. This is getting hairy, did you check the tach to see if the PCM is seeing the opti output when you spin it by hand? Also (this is not first hand, maybe one of the experts can chime in here) I have read that during cranking if the TPS voltage is above a certain level the computer reacts by cutting the injector pulses. It's the electronic version of sensing the old fashioned process to clear a flooded carburetor engine by holding the accelerator pedal open while cranking. Could be a long shot to check the TPS voltage. Man if you got opti pulses and voltage the darn ECM should fire (ground) the injectors about 4 ms during cranking. To bad you don't have access to another ecm to swap in there.

tonydee64

Thank you for the response. Well, I have a tip for everyone.... Do no trust a test light to determine if you have injector pulses. I have no idea why, but my test light failed to pick up the pulses, but I was finally able to purchase a noid light this morning and low and behold, I now have injector pulses. I dug in deep into the ecm harness last night and I don't know if I happened to unground something... dunno..

Anyway, I took out all of the old (non-premium) fuel and put premium in its place. It made no difference. Now the car starts sometimes (I still think the new opti is bad as intermittently produces no spark) and will idle perfectly..... BUT.... the second you give it gas it falls on its face....pop, backfires.... and shuts off.. Sometimes I can get it restarted... sometimes I can't. The other thing I wondered about was perhaps my O2 sensors are bad. I know the previous owner disabled two of the O2 sensors when he added headers and removed the cat. converter...the wires for the removed cats has been puklled from the ecm harness, and they show a constant .445 volts... (they've always been like that since I've owned the car).

Anyway.. I am getting the following O2/fuel trim readings:

O2S12V .445
O2S21V .720
O2S22V .445

ST FTRM1% -1.0
LT FTRM 1% 7.8
ST FTRM 2% 1.5
LT FTRM 2% .8-3.4

Although I'm not surem, it looks like maybe a lack of fuel is causing the LT FTRM 1% to try and add fuel to comensate... although I'm not sure.

alaureano

I Cant Remember Where I Read This But I Think The Fuel Pump Relay Does Have
Circuit That Controls The Injectors. My Wifes 1994 Z28 Had The Same Problems. I Found Out It Was The Pump Relay Because I Kicked The Driver Side Kick Panel Were The Relay Is Located. But A 1996 Ta May Have A Different Set Up. I Could Be Wrong But Give The Simple Stuff A Try. The Oil Presure Sensor Will Not Cut The Engine Out On 1994 Camaros.i Know This For A Fact When I Was Helping Someone Remove The Transmission And Something Got Caught In The Harness And Reipped The Whole Connector Out Of T He Sensor. Disconnecting The O2 Sensor Wont Shut It Down But Just Keep It In Open Loop. Rear O2 Sensors Only Monitor The Cats. I Would Think That If You Having A Problem With The Vats System Would Leave A Code. Not All Scaners Are Able To Read The Bcm Section Of The Car. Only A Gm Tech 2 Scanner Will Give You The Info You Need On Body And Srs Systems Of The Car. Can Your Scanner Acces The Vatts System.

alaureano

Also I Dont Remember The Vats Being In Constant Comunication With Pcm And Can Shut The Car Down While You Are Driving. If You Do Have A Problem With Vats Your Security Light Should Stay On Indicating A Problem And The Starter Wont Even Turn On. This Can Happen If You Get Grease On The Keys And You Try To Turn The Car On. The Resistence Value Being Read Has Changed Due To The Grease Covering The Resistor. Another Fine Example Was When I Had A Customer Show Me That It Was Able To Remove The Key. From The Ignition On A 1994 Z28 And The Car Ran Fine And Would Never Shut Off.

tonydee64

No, my little Actron scanner doesns't scan much... I'm still thinking it might be my fuel pump.... When I was draining my tank today of the 87 octane gas, I disconnected the fuel filter and shot the hose into a shallow bucket.... I don't know, I just didn't think the gas was GUSHING out of hose end ... it was coming out pretty good, but not gushing.... Can anybody see anythoing wrong with my O2 readings.....?

Oh, and I bought a brand new $53 fuel relay today from the Chevy dealer today... made no difference whatsoever. My security light has never flashed or stayed on through all of this.

alaureano

O2s22v .445 This Is The Sensor After The Cat On Bank 2. Was This A Stable Reading? If So Its Fine. If Your Car Has Cats This Reading Should Stay Stable Indicating The Cats Are Doing There Job. O2s22v .445 This Should Also Be An O2 Sensor After The Cat. If You Dont Have Cats Then Dont Worry About Those Readings. O2s21v .720 This Should Be An O2 Sensor Reading Before The Cat And Should Not Be Stable. It Should Rises And Fall Fairly Quickly.