Engine Problems (Starting & Missing)
10-30-2002, 01:57 AM
#1
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Posts: n/a
Engine Problems (Starting & Missing)
I have a 1990 300ZX 2+2 with 86K miles. Over the last couple of months my oil pressure began dropping lower than normal for short times (would drop down to about 10 - 15 psi at idle from standard of just below 30 psi) but then would go back up shortly later. Later, the car began to idle rough and began missing. I replaced the air filter and all the spark plugs, and the 2 spark plugs nearest the firewall contained much more carbon than the other 4. I thought that would solve my problem however things became worse. The missing became worse and my mileage dropped by about 15% (as if one cylinder was not firing) and then the engine began to have problems starting. I left on vacation for 2 weeks and upon returning the car will not start (it cranks - the battery is fully charged). I tested each cylinder to make sure they are receiving sparks and they are. I then tested the compression on each cylinder and they are what I am told are too low. The compression was between 25 and 50 psi. depending on the cylinder and I was told it should be up over 100psi. I thought it may be because all the oil had drained off the rings so I took out all the plugs to make sure they were not flooded from cranking and sprayed WD40 in the cylinder to help temporarily seal them and then tried starting the car. It made one attempt at starting but didn't make it and then just cranked. My friend thinks that this indicates that my piston rings and/or valves are not sealing and I need to overhaul my engine however I am praying there is something else that someone can suggest I try first. It just seems like this is a bit extreme for only 86K miles. If it does require an overhaul do you think it was caused by this lower oil pressure (my oil pump)? Has anyone heard of anyone experiencing this fluctuating oil pressure at idle. There was never a standard time that the oil pressure fluctuation occurred (some times when the engine was hot and sometimes when it was cold). Any suggestoins on possible simple remedies to get my Z running?
Thanks for any advice you can give me.
Thanks for any advice you can give me.
10-30-2002, 07:51 PM
#2
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Re: Engine Problems (Starting & Missing)
sounds like it is toast. I just replaced my friends engine that did the exact same thing. Probably jumped time a little and threw a rod. So crank is prob bad and I bet you valves are wore out. Has the car had a hard life. Probably so. Alot of people abuse these cars more than taking care of them. Tr zxparts@mindspring.com. He is really great on rebuilt or used engines. This is were we got my friends replacement. We bought a 93 engine with 40k on it. Dropped it in and it woked great. I did have to replace the motor mounts and I went a head and replaced the rear main seal, timing belt, water pump and thermostat as a precaution. Only way to find out for sure is to tear it down. Goodluck.
10-30-2002, 08:19 PM
#3
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I bet 99.9%
It is your injectors. They are notorious to go out in Z's after 80k miles. Running rough and misfires are a sure sign of bad injectors. Than would also explain your poor compression. If I am correct compression is checked by pulling the spark plugs, right, to avoid the firing of the a/f mixture (and to have a place to check compression). Well if you have bad injectors , no fuel is entering the cylinder thus giving you incorrect compression readings. 2-3 injectors go bad, your Z won't run. All 6 of mine have gone bad and my Z has 104K miles.
As far as you oil pressure is concerned, don't worry about it. As long as you have oil in the engine and check and change it regularly your fine. The oil sender unit is also prone to go bad in Z's. Which just gives you inaccurate pressure reading but the oil pressure inside the engine is fine. On that note normal oil pressure reading are on a hot engine, 3-5 psi idling, 30 psi normal driving 60-80 psi hard driving.
As far as you oil pressure is concerned, don't worry about it. As long as you have oil in the engine and check and change it regularly your fine. The oil sender unit is also prone to go bad in Z's. Which just gives you inaccurate pressure reading but the oil pressure inside the engine is fine. On that note normal oil pressure reading are on a hot engine, 3-5 psi idling, 30 psi normal driving 60-80 psi hard driving.
10-31-2002, 12:22 AM
#4
Registered User
Join Date: Oct 2002
Posts: 13
Re: Engine Problems (Starting & Missing)
86,000 miles and your baby doesn't want to run...I hate when shnap like that happens.
In my opinion your engine still has life because you never stated that your plugs where caked with carbonized oil soot. As for the low compression issue, how was it done?
What type of compression tester did you use (screw in or push in)? If you screwed it then your testing should be fairly accurate if and only if you cranked the engine over enough times.
Each manufacturer bases compression testing on the amount of revolutions the engine is cranked or how fast the engine is turning over. Did you crank the motor the recommended amount of revolutions? Usually compression testing is to be done with a warm engine but it's obviously impossible to warm up an engine that doesn't run. Compression will be low if the tester was not completely snugged into the spark plug orifice. One way to determine if your rings are totally shot is to perform the leak down test. All you'd have to do is pour about a spoon full of engine oil down the spark plug hole screw the tester in and crank the engine let's say four times. If the compression increases in comparison to "no lube" poured into the hole (@four cranks) then you have ring problems otherwise the rings are fine. A healthy engine produces about 130-150 psi.
Have you checked the ECU for any trouble codes? This should be one of the very first procedures completed before getting your hands dirty. There are two ways to set the ECU into diagnostic mode.
#1 Remove the passenger side floorboard and turn the diagnostic potentiometer on the ECU clockwise then back, or counterclockwise then back. My memory is terrible but I know that it's one of the two.
#2 Use a jumper wire (20 gauge stripped at both ends or thin gauge paper clip) to join the #8 and #9 pins on the grey connector by the drivers side kick panel. Facing the connector #8 and #9 are on the left bottom half of the 18 pin connector.
It's great that you checked for spark but at the same time did you smell for fuel? Since your plugs do arch look for codes related to the fuel system such as the fuel pump or injectors. Double check all fuses related to the fuel system including relays. Test the fuel pump and make sure that it still operates and still pressurizes fuel to the injectors.
An engine with no spark usually pollutes the engine bay with gasoline fumes. Stl300z is on the right track. You stated that "WD40 was sprayed into the cylinder to help temporarily seal them" and upon the attempted start-up it sounded as if your VG was going to start but didn't. The reason your VG30DE did not completely start is because it ran out of fuel (WD40). I used to play with WD40 when I was a kid and boy was it flammable. I'm sure I'm not the only kid who has made a flame thrower out of their dad's chemicals.
Do you have access to a regulated bottle of propane? This will be your temporary fuel. Tapping into the PCV intlets on the intake hose would be the best place to feed the propane into the engine since it's right by the throttle bodies. You may want to fabricate some sort of "T" fitting so each bank of cylinders receives the "fuel". Have an assistant either crank the engine or turn on the attached regulated propane bottle while the engine is being cranked. This allows the motor to suck in the flamable gas. Be sure to close the regulator valve shut before the engine is stopped. Remember, this is a dangerous procedure if done carelessly. Any spark can ignite residual propane so USE EXTREME CAUTION! KEEP A FIRE EXTINGUISHER NEAR BY.
You may want to avoid using a propelled flammable liquid. Some chemicals will destroy O2 sensors, gaskets, seals, ect... Your engine should start or at the least stumble once the flammable agent enters the combustion chamber. The cause lies between the injectors and fuel pump. Since Z32's have documented injector problems your troubleshooting direction should aim towards the injectors. Just remember, fuel pumps die too.
As for the oil pressure issue, Stl300z is correct. Most Z32 owners I have spoken with have the same symptoms. If your oil pump really did take a [censored] your VG30DE would have seized or threw a rod by now or maybe it's lasting because your running "Prolong". Mail me with any further questions.
Good luck troubleshooting.
Deric
In my opinion your engine still has life because you never stated that your plugs where caked with carbonized oil soot. As for the low compression issue, how was it done?
What type of compression tester did you use (screw in or push in)? If you screwed it then your testing should be fairly accurate if and only if you cranked the engine over enough times.
Each manufacturer bases compression testing on the amount of revolutions the engine is cranked or how fast the engine is turning over. Did you crank the motor the recommended amount of revolutions? Usually compression testing is to be done with a warm engine but it's obviously impossible to warm up an engine that doesn't run. Compression will be low if the tester was not completely snugged into the spark plug orifice. One way to determine if your rings are totally shot is to perform the leak down test. All you'd have to do is pour about a spoon full of engine oil down the spark plug hole screw the tester in and crank the engine let's say four times. If the compression increases in comparison to "no lube" poured into the hole (@four cranks) then you have ring problems otherwise the rings are fine. A healthy engine produces about 130-150 psi.
Have you checked the ECU for any trouble codes? This should be one of the very first procedures completed before getting your hands dirty. There are two ways to set the ECU into diagnostic mode.
#1 Remove the passenger side floorboard and turn the diagnostic potentiometer on the ECU clockwise then back, or counterclockwise then back. My memory is terrible but I know that it's one of the two.
#2 Use a jumper wire (20 gauge stripped at both ends or thin gauge paper clip) to join the #8 and #9 pins on the grey connector by the drivers side kick panel. Facing the connector #8 and #9 are on the left bottom half of the 18 pin connector.
It's great that you checked for spark but at the same time did you smell for fuel? Since your plugs do arch look for codes related to the fuel system such as the fuel pump or injectors. Double check all fuses related to the fuel system including relays. Test the fuel pump and make sure that it still operates and still pressurizes fuel to the injectors.
An engine with no spark usually pollutes the engine bay with gasoline fumes. Stl300z is on the right track. You stated that "WD40 was sprayed into the cylinder to help temporarily seal them" and upon the attempted start-up it sounded as if your VG was going to start but didn't. The reason your VG30DE did not completely start is because it ran out of fuel (WD40). I used to play with WD40 when I was a kid and boy was it flammable. I'm sure I'm not the only kid who has made a flame thrower out of their dad's chemicals.
Do you have access to a regulated bottle of propane? This will be your temporary fuel. Tapping into the PCV intlets on the intake hose would be the best place to feed the propane into the engine since it's right by the throttle bodies. You may want to fabricate some sort of "T" fitting so each bank of cylinders receives the "fuel". Have an assistant either crank the engine or turn on the attached regulated propane bottle while the engine is being cranked. This allows the motor to suck in the flamable gas. Be sure to close the regulator valve shut before the engine is stopped. Remember, this is a dangerous procedure if done carelessly. Any spark can ignite residual propane so USE EXTREME CAUTION! KEEP A FIRE EXTINGUISHER NEAR BY.
You may want to avoid using a propelled flammable liquid. Some chemicals will destroy O2 sensors, gaskets, seals, ect... Your engine should start or at the least stumble once the flammable agent enters the combustion chamber. The cause lies between the injectors and fuel pump. Since Z32's have documented injector problems your troubleshooting direction should aim towards the injectors. Just remember, fuel pumps die too.
As for the oil pressure issue, Stl300z is correct. Most Z32 owners I have spoken with have the same symptoms. If your oil pump really did take a [censored] your VG30DE would have seized or threw a rod by now or maybe it's lasting because your running "Prolong". Mail me with any further questions.
Good luck troubleshooting.
Deric
10-31-2002, 01:23 AM
#5
Guest
Posts: n/a
Re: Engine Problems (Starting & Missing)
donkayroo, stl300z, & bjz:
Thanks very much for the advice!!! We will be trying some of your thoughts as we continue to work to determine my problem and I will continue to post what we determine for those interested.
As for the compression test, we used the screw in kind. Also, every cylinder is getting gas as we checked all the spark plugs after cranking and they were all very wet with gas. We performed a leak down test on cylinder #1 (as an indicator of all the cylinders) earlier tonight (without adding the spoon full of oil) and it held no pressure at all. We performed the test when the cylinder was at TDC (top dead center) on successive rotations so that we were sure we were getting it on the compression stroke and not the exhaust stroke. Our guess is that because the 70 psi of pressure we put into the cylinder dropped immediately (less than a second) that my timing belt has slipped a notch and the valves are open at TDC on the compression stroke but luckily the timing belt has not slipped enough to cause the valves to contact the piston. (The timing belt slipping hypothesis is the only rational explanation that my dad and I can come up with that would explain all the cylinders’ compressions dropping at the same time.) What are your thoughts on this? Is there a way to determine whether the timing belt has slipped a notch without going through all the crap to access the timing belt. Is there any way to do this with the diagnostics mentioned?
Thanks again for your time and knowledge!
Eric
Thanks very much for the advice!!! We will be trying some of your thoughts as we continue to work to determine my problem and I will continue to post what we determine for those interested.
As for the compression test, we used the screw in kind. Also, every cylinder is getting gas as we checked all the spark plugs after cranking and they were all very wet with gas. We performed a leak down test on cylinder #1 (as an indicator of all the cylinders) earlier tonight (without adding the spoon full of oil) and it held no pressure at all. We performed the test when the cylinder was at TDC (top dead center) on successive rotations so that we were sure we were getting it on the compression stroke and not the exhaust stroke. Our guess is that because the 70 psi of pressure we put into the cylinder dropped immediately (less than a second) that my timing belt has slipped a notch and the valves are open at TDC on the compression stroke but luckily the timing belt has not slipped enough to cause the valves to contact the piston. (The timing belt slipping hypothesis is the only rational explanation that my dad and I can come up with that would explain all the cylinders’ compressions dropping at the same time.) What are your thoughts on this? Is there a way to determine whether the timing belt has slipped a notch without going through all the crap to access the timing belt. Is there any way to do this with the diagnostics mentioned?
Thanks again for your time and knowledge!
Eric
10-31-2002, 05:30 PM
#6
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Posts: n/a
Re: Engine Problems (Starting & Missing)
Another thing that came to mind is some early 90s Z's had what is called soft valves. After wear the valve ends become razor sharp and brittle. Causeing the same effect as your theory with the slipped timing belt.
11-01-2002, 07:52 AM
#7
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Posts: n/a
couple things...
a) oil pressure. The oil pressure sending unit in the Z is notoriously bad. On my last one, and just about every other Z I've ever seen, they eventually go flaky. They are cheap, so get a new one before you think your oil pressure has completely died.
b) fuel. The plugs may be wet, big deal...are you getting ENOUGH fuel? Go buy a cheap inline fuel pressure guage and hook it up after the fuel filter. Check to make sure your fuel pressure isn't dropping right off after an initial charge up. If it does, there are several options. The fuel pump in the Z is near bulletproof, but the fuel pump controller is also pretty notorious. You can go to www.twinturbo.net and search in the Tech forum for 'my91z'. He posted a procedure to bypass the controller, basically hotwiring the fuel pump. If it starts then, that is your problem.
c) more fuel... have you changed your filter recently?
d) spark. You check all the spark plugs to make sure they are firing?
e) eletrical connections. Clean both harness connections to the PTU and the CAS.
91 300ZX TT. Lots of mods, check Rides under my Profile if you are interested.
b) fuel. The plugs may be wet, big deal...are you getting ENOUGH fuel? Go buy a cheap inline fuel pressure guage and hook it up after the fuel filter. Check to make sure your fuel pressure isn't dropping right off after an initial charge up. If it does, there are several options. The fuel pump in the Z is near bulletproof, but the fuel pump controller is also pretty notorious. You can go to www.twinturbo.net and search in the Tech forum for 'my91z'. He posted a procedure to bypass the controller, basically hotwiring the fuel pump. If it starts then, that is your problem.
c) more fuel... have you changed your filter recently?
d) spark. You check all the spark plugs to make sure they are firing?
e) eletrical connections. Clean both harness connections to the PTU and the CAS.
91 300ZX TT. Lots of mods, check Rides under my Profile if you are interested.
11-01-2002, 07:58 AM
#8
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Posts: n/a
one other thing. I assume you are in Austin, TX?
if so..my god man, you have one of the largest collection of Z32 enthusiasts anywhere! ...but they dont hang out here. Go to www.z32.org and post you need help. All the guys there are cool, and most of them are very knowledgeable. I'm sure some of them would be more than glad to help you. And they can come armed with the right equipment.
91 300ZX TT. Lots of mods, check Rides under my Profile if you are interested.
91 300ZX TT. Lots of mods, check Rides under my Profile if you are interested.
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