Replaced Opti,timing chain, plugs/wires, coil, icm. Car STILL stumbles on face
07-30-2009, 07:20 PM
#1
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Replaced Opti,timing chain, plugs/wires, coil, icm. Car STILL stumbles on face
Hey Ive been dealing with this problem for three years now, and i finally got around to replacing parts. The car (94 z28) stumbles and will stall on hard acceleration of the throttle from a stop, or when car is running hot. Once the car reaches around 2500 rpms you can mash the throttle to the floor and there is no stumble. But at idle if you give it more than 1/3 throttle the car will buck and the rpms will drop and sometimes stall. So ive searched tirelessly on the forums for the last few years as to a solution, and have been told its my optispark. So this week i replaced the optispark with a new unit and replaced the fuel filter, spark plugs & wires, water pump, and timing chain. Have also tried different coils and icms, albeit from chevy vans.
But with no avail, car still stumbles at low rpms, and hard to start (cranks alot when engine is warm or just turned off recently). I also hollowed out the catalytic converter. One really weird thing is that we checked the ohms on the fuel injectors and they are all at 15 ohms, but they are not receiving an injector pulse, but car still starts and runs. The optispark i installed has a small tube on the bottom, not sure if that is a vaccum line since i should have a nonvented unit I really need to get this thing fixed cause its sitting in my friends shop on a lift for almost the whole week and hes loosing business because of it, We are just at our wits end, we really cant figure out what could be causing the problem. I really would appreciate it if anyone could chime in with any ideas, I'm up to try anything at this point to get this car running right. Thank you and sorry for the long post.
Dan
(p.s. sorry for any grammatical errors I've been up far to long lol)
But with no avail, car still stumbles at low rpms, and hard to start (cranks alot when engine is warm or just turned off recently). I also hollowed out the catalytic converter. One really weird thing is that we checked the ohms on the fuel injectors and they are all at 15 ohms, but they are not receiving an injector pulse, but car still starts and runs. The optispark i installed has a small tube on the bottom, not sure if that is a vaccum line since i should have a nonvented unit I really need to get this thing fixed cause its sitting in my friends shop on a lift for almost the whole week and hes loosing business because of it, We are just at our wits end, we really cant figure out what could be causing the problem. I really would appreciate it if anyone could chime in with any ideas, I'm up to try anything at this point to get this car running right. Thank you and sorry for the long post.
Dan
(p.s. sorry for any grammatical errors I've been up far to long lol)
Last edited by 9T4Z28; 08-01-2009 at 11:40 AM.
07-30-2009, 08:50 PM
#2
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Find a way to monitor fuel pressure - put a gauge on the schrader valve - and see if it drops when you mash the pedal.
Also, get your car on a scanner and see what's going on.
You also might try disconnecting the MAF sensor in case that is an issue.
Also, get your car on a scanner and see what's going on.
You also might try disconnecting the MAF sensor in case that is an issue.
07-30-2009, 09:01 PM
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hey ive tried it with and without the MAF sensor attached. Ill run it for codes again tomorow, but i think i remember a DTC 16 from years ago low resolution pulse code, not sure tho. As for the Fuel pressure we checked it and it read 39-40 when key on, engine off. and with engine running it was around the same, as for WOT i will test tomorrow.
07-31-2009, 03:59 PM
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So i cleared the codes and this came back:
83- torque converter quad driver module
36- High resolution pulse failure
48- mass air flow system failure
18- crank signal open or no signal
As for the MAF sensor we have tried it unpluged and it makes no difference. One weird thing is that the voltage on the PCM ignition fuse fluctuates up and completely to zero while cranking the car.... Really need to get this thing fixed im driving a 78 Datsun 280z right now cause of it lol HELP me please
83- torque converter quad driver module
36- High resolution pulse failure
48- mass air flow system failure
18- crank signal open or no signal
As for the MAF sensor we have tried it unpluged and it makes no difference. One weird thing is that the voltage on the PCM ignition fuse fluctuates up and completely to zero while cranking the car.... Really need to get this thing fixed im driving a 78 Datsun 280z right now cause of it lol HELP me please
07-31-2009, 04:42 PM
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Clean Connections
You could start by cleaning all the positive and negative connections under the hood that you can. Disconnect the neg bat cable and remove all the wires from the + junction box , clean and re-install. Do the same with any ground connections that you can get to. Just a thought but may help out.
08-01-2009, 09:11 AM
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Ive checked pretty much every ground i could find. My friend thinks it may be the PCM which is bad but hes not sure. I really need help cause no one around here has any experience or real no how of the LT1. And the codes I posted before, when i search for meanings or solutions to them, I find that the codes have more than one meaning. Especially when i look at Shoebox website. So confused and the car is just sitting in the shop. I do have an exhaust leak on the driver side exhaust manifold, sounds like its from there, that gets faster the more you hit the throttle. This car is depressing me... Please someone help.
08-01-2009, 10:46 AM
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Hey have been on the boards all day searching things, and the optispark i installed looks like it has a vaccum tube on the bottom of it. The non-vented opti, other than then the connections to the plug wires and harness connection, is there any tubes?
08-01-2009, 11:21 AM
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I just realized i made a mistake in my first post, i was under the belief it was an AC Delco Optispark we installed, and its not. I believe its aftermarket. It doesn't bear any logos but does have a small tube on the bottom.
Another question, lol i have lots of questions and no answers, could the o2 sensors cause hesitation and bogging while hard acceleration from idle or slow speed. My problem exists when car is just started (cold) and when it is at operating temperature, more so when the car is running hotter than normal (i.e. lots of traffic or hot humid weather).
Someone please put me out of my misery, my head is churning and I cant solve anything on my own.
Thank you guys for reading this, any (i mean any) ideas are gratefully appreciated.
- Dan
Another question, lol i have lots of questions and no answers, could the o2 sensors cause hesitation and bogging while hard acceleration from idle or slow speed. My problem exists when car is just started (cold) and when it is at operating temperature, more so when the car is running hotter than normal (i.e. lots of traffic or hot humid weather).
Someone please put me out of my misery, my head is churning and I cant solve anything on my own.
Thank you guys for reading this, any (i mean any) ideas are gratefully appreciated.
- Dan
Last edited by 9T4Z28; 08-01-2009 at 11:37 AM.
08-01-2009, 12:31 PM
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Ive been told the EGR valve, if it is shot can cause such problems, is this true?
And if the coil is sufficient would it cause the sputtering and hesitation at low rpms, even though acceleration is fine at higher rpms?
And if the coil is sufficient would it cause the sputtering and hesitation at low rpms, even though acceleration is fine at higher rpms?
08-01-2009, 01:11 PM
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Ive been told the EGR valve, if it is shot can cause such problems, is this true?
And if the coil is sufficient would it cause the sputtering and hesitation at low rpms, even though acceleration is fine at higher rpms?
And if the coil is sufficient would it cause the sputtering and hesitation at low rpms, even though acceleration is fine at higher rpms?
08-01-2009, 01:22 PM
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Start by using the correct code list for an LT1. Your 94 does not have a "quad driver module", 93 was the last year. Shoebox has it online, but it appears you didn't use his definitions:
http://shbox.com/1/Dtcs.htm
DTC 83 = Reverse inhibit system (manual transmission)
TCC PWM Solenoid Circuit Fault (automatic transmission)
Since you have an automatic, you have a problem with the torque converter pulse width modulation solenoid.
DTC 36 = Distributor ignition system (faulty high resolution pulse or extra low resolution pulse detected)
That means the PCM could not find the high res pulse from the Opti. Did you ever check or replace the short harness from the gray connector on the bracket on the passenger side of the intake manifold, to the Opti? Corrosion or damaged pins are possible. If the "clip" that locks the connectors together is broken you will have problems.
DTC 48 = Mass Air Flow (MAF) sensor circuit
Check for 12V between the pink wire and the black/white wire in the connector. Check the sensor signal frequency between the yellow and the black/white wire. Substitute a known "good" MAF sensor.
DTC 18 = 18 Injector circuit(s) (nothing to do with the "crank signal")
One or more of the injectors has a circuit fault. You've already verified 15ohm across the injector pins, so the injectors are not the problem. Now look for 12V on the pink wire at each injector connector, when measured to an engine ground. There is no way the injectors will fire without the ground pulse from the PCM. How did you determine you are not getting a ground pulse to each injector? You need to use a "noid" light. Set will cost about $15. The light will pulse as the ground is provided and the circuit is completed.
If your EGR is stuck open, it will cause a rough idle, and stalling. At idle, either pull a vacuum on the connection at the EGR valve, or reach through the base of the valve to the diaphragm and force it open. If the engine runs worse, its not likely the EGR valve. If is doesn't change when you open the valve, and is running rough, but exactly the same as with the valve "closed", you may have found your problem.
Have you ever checked your air inlet elbow (bellows) for tears (the elbow between the MAF and throttle body)?
Have you ever tested the coolant temperature sensor, mounted in the water pump housing? Shoebox has instructions.
Check the fuel pressure at WOT with the engine at full load/max RPM. Should not drop below 40psi.
Check the throttle position sensor voltage, to make sure there are no voltage dropouts or spikes as you slowly rotate the blades. Should be about 0.67V at closed throttle, and increase by about 4V at WOT.
http://shbox.com/1/Dtcs.htm
DTC 83 = Reverse inhibit system (manual transmission)
TCC PWM Solenoid Circuit Fault (automatic transmission)
Since you have an automatic, you have a problem with the torque converter pulse width modulation solenoid.
DTC 36 = Distributor ignition system (faulty high resolution pulse or extra low resolution pulse detected)
That means the PCM could not find the high res pulse from the Opti. Did you ever check or replace the short harness from the gray connector on the bracket on the passenger side of the intake manifold, to the Opti? Corrosion or damaged pins are possible. If the "clip" that locks the connectors together is broken you will have problems.
DTC 48 = Mass Air Flow (MAF) sensor circuit
Check for 12V between the pink wire and the black/white wire in the connector. Check the sensor signal frequency between the yellow and the black/white wire. Substitute a known "good" MAF sensor.
DTC 18 = 18 Injector circuit(s) (nothing to do with the "crank signal")
One or more of the injectors has a circuit fault. You've already verified 15ohm across the injector pins, so the injectors are not the problem. Now look for 12V on the pink wire at each injector connector, when measured to an engine ground. There is no way the injectors will fire without the ground pulse from the PCM. How did you determine you are not getting a ground pulse to each injector? You need to use a "noid" light. Set will cost about $15. The light will pulse as the ground is provided and the circuit is completed.
If your EGR is stuck open, it will cause a rough idle, and stalling. At idle, either pull a vacuum on the connection at the EGR valve, or reach through the base of the valve to the diaphragm and force it open. If the engine runs worse, its not likely the EGR valve. If is doesn't change when you open the valve, and is running rough, but exactly the same as with the valve "closed", you may have found your problem.
Have you ever checked your air inlet elbow (bellows) for tears (the elbow between the MAF and throttle body)?
Have you ever tested the coolant temperature sensor, mounted in the water pump housing? Shoebox has instructions.
Check the fuel pressure at WOT with the engine at full load/max RPM. Should not drop below 40psi.
Check the throttle position sensor voltage, to make sure there are no voltage dropouts or spikes as you slowly rotate the blades. Should be about 0.67V at closed throttle, and increase by about 4V at WOT.
Last edited by Injuneer; 08-01-2009 at 01:27 PM.
08-01-2009, 01:43 PM
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I apologize Fred, I wrote the first post before I looked at the true definitions provided by Shoebox, and as for testing the injectors I did you the "noid" light and it would not light up(checked on a different car and the light worked properly).
As for the elbow, I have a vortech(?) metal elbow from when i bought it. We have tried a MAF sensor from an Impala SS, which does make it start better, but nothing for the actual stumble. We tested the coolant sensor, before and after we flushed the system. It read negative 8 million something degrees, that was baffling to say the least so we changed it. As for the EGR valve, could it still be the culprit if the car dosen't stall while at idle. The idle does fluctuate some but usually it is around 900 rpms or so with jumps to 1000 rpms or down to 800ish rpms.
As for testing the maf sensor wiring and the injector wiring I will have to wait till monday, but do you have an ideas on why the PCM ignition fuse fluctuates voltage when the car is running, but it dosent while the key is on and engine is off.
Thank you for the insight at least now I have some where to go from, I trully appreciate it.
p.s. the DTC for the transmission what symptoms would that produce ?
As for the elbow, I have a vortech(?) metal elbow from when i bought it. We have tried a MAF sensor from an Impala SS, which does make it start better, but nothing for the actual stumble. We tested the coolant sensor, before and after we flushed the system. It read negative 8 million something degrees, that was baffling to say the least so we changed it. As for the EGR valve, could it still be the culprit if the car dosen't stall while at idle. The idle does fluctuate some but usually it is around 900 rpms or so with jumps to 1000 rpms or down to 800ish rpms.
As for testing the maf sensor wiring and the injector wiring I will have to wait till monday, but do you have an ideas on why the PCM ignition fuse fluctuates voltage when the car is running, but it dosent while the key is on and engine is off.
Thank you for the insight at least now I have some where to go from, I trully appreciate it.
p.s. the DTC for the transmission what symptoms would that produce ?
Last edited by 9T4Z28; 08-01-2009 at 02:11 PM.
08-01-2009, 07:33 PM
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Connections
So..you have taken all the positive cables loose from the junction box and given them a good cleaning? Just a thought that it could contribute to low voltage to your injectors if they are corroded in any manner.
08-02-2009, 06:42 PM
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I will try the junction box tomorrow when the shop opens, since its been closed all weekend. I downloaded Datamaster trial, could anyone tell me how to run it so that people on this forum would understand it? Is it self explanatory? Im going to export to an excel file, since Ive read thats easier to explain. Hopefully something there will help resolve the issues.
P.s. I havent been to the shop to test out what you've advised me Injuneer, and will do so tomorrow morning.
P.s. I havent been to the shop to test out what you've advised me Injuneer, and will do so tomorrow morning.
Last edited by 9T4Z28; 08-02-2009 at 06:47 PM.
08-02-2009, 07:26 PM
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Just another idea, I've been thinking about. Sorry guys i rant so much, but sitting here not being able to actually test things makes my mind go places. The question is when installing an 94 optispark, is it possible to place the dowel wrong and still have the car start and idle acceptable, but have the issue with the low rpm stumble as i have?