85c4 oil psi fluctuating higher than normal
07-29-2014, 08:34 AM
#1
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85c4 oil psi fluctuating higher than normal
So I am a new corvette owner for the first time. I've done a lot of work with it so far getting it to run decently without having to take it to a shop but having no mechanical expertise and a chev shop manual I'm getting only so far. Now my new problem is this. I changed the oil in it to a 10w30 conventional not knowing anything after is sat for about 8 yrs. I quickly changed it to compcam r 15w50 conventional for it had the correct oil supplement for the engine. It started worse and idled rough. So I brought it in and the Distributer was 8 deg retarded. Had a custom maf they replaced to a stock maf. After getting the paperwork on the car I found out it was using Mobil 1 15w50 so I recently changed it to that over the weekend. I used a Mobil 1 filter which is smaller then the normal ones but after calling Mobil 1 they said it would be completely fine. Well it's not. It has a small leak forming on the bottom of the drain pan still need to get it up and cleaned to find that but it only leaks when it's warmed up and running. When I park it I wiped off pan and put towel down to spot leak in morning but no drips. my pressure keeps fluctuating now. Normally it's says 65 start up. It drops to 32lowest at a stop light and then back to 65 like normal. Now that I changed the oil it's fluctuating from 50-70 psi and it drops when I accel and rises when I let off the gas. I can be at 1700rpm steady gas pressure and psi fluctuates from 66-52. It never drops below 40 when at a red light. It doesn't want to start till the third time as well and idles like crap and the rpms are bouncing and never staying steady. Also the rpm skyrocketed when I changed the oil to Mobil so I tried adjusting the idle screw to get it to drop but it's fine when it's cold but when it warms up it seems I adjusted it too low. I'm lost and figure it's time to maybe bring in and have a shop. Any ideas. Also only 49k miles.
Last edited by Bigpappawoowoo; 07-29-2014 at 09:09 AM. Reason: Bad word.
07-29-2014, 09:19 AM
#2
OK,
This is gonna be brief because of time allowed but it'll be straight forward and a little harsh....
OIL has NOTHING to do with how it idles or runs unless you are in Antarctica.
ANY oil is good oil as long as its clean. Older engines high miles can use a heavy oil like 15/50. Newer tighter engines should stick to 10/40 or 10/30.
The FACTORY SERVICE MANUAL (2 book set from GM) is the Bible ! using ANY other book like chiltons, or the other store bought crap is sacrilege. Sinful and will cause you problems. Those books contain ZERO C4 specific info.
Your oil psi bouncing around is caused by a dirty or lose OPS connection. This is an ELECTRIC sensor. The cleanliness of the contact is critical for accurate signals to the dash gauge. If that wire is lose or dirty the signal will only be as good as the contact. The sender may be faulty as well. OP is the big bulb sensor. The smaller 2 wire sensor is for low pressure for the fuel pump.....READ up on THAT system. You will need to....its a back up system for the fuel pump relay so the car can still start after the fuel relay has died. Learn it.
Default for a d/c oil press sensor is 80 psi.
The engine performance comes from MANY things ALL being set right.. TPS, MAF, relays air temp sensors, coolant temp sensors etc....ALL.
You have a unique trouble code system that tells you what to look at when there IS trouble under the hood. LEARN how to use that and learn how to work with it. No, it does NOT say "fix this or that"....it simply tells you what system is effected and that gives the knowledgeable mechanic a place to look.
What codes is the engine giving you?????????? If you do not know, FIND OUT. Learn Flash Codes.
Don't bother trying to work on this engine without the right test tools.......
fuel pressure test gauge
spark tester
noid lite
DVM (digital volt meter)
timing light
vac tester/pump
test lite
Some basic tips.....
clean and secure ALL electrical contacts/connections under the hood. ALL.
Make damn sure that the grounds are clean and tight. The grounds are how the ECM operates the engine....NOT the power or hot wires.
The most important grounds are on a bolt over the oil filter.
Use ONLY delco modules and coils in the distributor. Do NOT use gimmick wire sets. Use Delco if you want to be sure of the performance of the parts.
Learn about THIS high pressure fuel system. Learn how and WHY it runs the pump and WHEN. Learn what the gauge should look like. Hint: you should see 40 psi without the eng ever firing.
oil gets thin when it gets hot,. so psi goes down when hot. 25 psi idle is great,. 45-60 cruising hot is great. 12 psi hot idle is ok but that's as low as you want to go.
New leaks/ old leaks have nothing to do with the brand or wt of the chosen oil. They were there before.
Clean and secure ALL electrical connections from the battery area, behind the battery especially, and ALL the sensor plugs.
Trace ALL vac hoses and fittings. They are ALL necessary. It does NOT matter one fuc&ing bit what your last car had or used. This is a C4...different animal than you've ever worked on. It goes fast because of all this extra stuff. Respect the stuff !
Respect the FSM and what it has to say. Learn the flash code system and how to read it.
Above all else, understand that the grounds are the key to this engines running. NOT the hot wires.
If you need a REAL FSM book set, look on FleaBAy for your yr model and they have lots for sale, pretty cheap now. Under $50 for both books.
Half the fun of picking up a basket case is fixing a basket case. There is a great deal of satisfaction in that.
Have fun!
and,
welcome to Corvettes !
This is gonna be brief because of time allowed but it'll be straight forward and a little harsh....
OIL has NOTHING to do with how it idles or runs unless you are in Antarctica.
ANY oil is good oil as long as its clean. Older engines high miles can use a heavy oil like 15/50. Newer tighter engines should stick to 10/40 or 10/30.
The FACTORY SERVICE MANUAL (2 book set from GM) is the Bible ! using ANY other book like chiltons, or the other store bought crap is sacrilege. Sinful and will cause you problems. Those books contain ZERO C4 specific info.
Your oil psi bouncing around is caused by a dirty or lose OPS connection. This is an ELECTRIC sensor. The cleanliness of the contact is critical for accurate signals to the dash gauge. If that wire is lose or dirty the signal will only be as good as the contact. The sender may be faulty as well. OP is the big bulb sensor. The smaller 2 wire sensor is for low pressure for the fuel pump.....READ up on THAT system. You will need to....its a back up system for the fuel pump relay so the car can still start after the fuel relay has died. Learn it.
Default for a d/c oil press sensor is 80 psi.
The engine performance comes from MANY things ALL being set right.. TPS, MAF, relays air temp sensors, coolant temp sensors etc....ALL.
You have a unique trouble code system that tells you what to look at when there IS trouble under the hood. LEARN how to use that and learn how to work with it. No, it does NOT say "fix this or that"....it simply tells you what system is effected and that gives the knowledgeable mechanic a place to look.
What codes is the engine giving you?????????? If you do not know, FIND OUT. Learn Flash Codes.
Don't bother trying to work on this engine without the right test tools.......
fuel pressure test gauge
spark tester
noid lite
DVM (digital volt meter)
timing light
vac tester/pump
test lite
Some basic tips.....
clean and secure ALL electrical contacts/connections under the hood. ALL.
Make damn sure that the grounds are clean and tight. The grounds are how the ECM operates the engine....NOT the power or hot wires.
The most important grounds are on a bolt over the oil filter.
Use ONLY delco modules and coils in the distributor. Do NOT use gimmick wire sets. Use Delco if you want to be sure of the performance of the parts.
Learn about THIS high pressure fuel system. Learn how and WHY it runs the pump and WHEN. Learn what the gauge should look like. Hint: you should see 40 psi without the eng ever firing.
oil gets thin when it gets hot,. so psi goes down when hot. 25 psi idle is great,. 45-60 cruising hot is great. 12 psi hot idle is ok but that's as low as you want to go.
New leaks/ old leaks have nothing to do with the brand or wt of the chosen oil. They were there before.
Clean and secure ALL electrical connections from the battery area, behind the battery especially, and ALL the sensor plugs.
Trace ALL vac hoses and fittings. They are ALL necessary. It does NOT matter one fuc&ing bit what your last car had or used. This is a C4...different animal than you've ever worked on. It goes fast because of all this extra stuff. Respect the stuff !
Respect the FSM and what it has to say. Learn the flash code system and how to read it.
Above all else, understand that the grounds are the key to this engines running. NOT the hot wires.
If you need a REAL FSM book set, look on FleaBAy for your yr model and they have lots for sale, pretty cheap now. Under $50 for both books.
Half the fun of picking up a basket case is fixing a basket case. There is a great deal of satisfaction in that.
Have fun!
and,
welcome to Corvettes !
Last edited by leesvet; 07-29-2014 at 09:26 AM.
07-29-2014, 09:35 AM
#3
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Ok.
Ok. First I do have a Chevrolet dealer shop manual for it. The Hanes is crap for it. Second no trouble codes are present. I checked for that yesterday. The oil leak hasn't been there for the past 2 months and just started sat morn after I changed the oil fri night. Figured it might just be residual from the change but there's been a small spot after I stop driving 30 min later. So it's new.
07-29-2014, 09:52 AM
#4
Ok. First I do have a Chevrolet dealer shop manual for it. The Hanes is crap for it. Second no trouble codes are present. I checked for that yesterday. The oil leak hasn't been there for the past 2 months and just started sat morn after I changed the oil fri night. Figured it might just be residual from the change but there's been a small spot after I stop driving 30 min later. So it's new.
you're ahead of the curve.....
Heres a big clue.
the ONLY system on the car that has no system for a trouble code is the FUEL system.
IF you are positive the SES lite is actually working, then start going thru the fuel system, and test and confirm each piece. Pressures, pump run times, relays etc. Filters,. intake and external.
and finally, if no one else has said it, your stock fuel injectors are JUNK and cannot be counted on to do anything right. Ohms test and do leakdown test but while you do that have Jon at FIC ship you a set of Bosch-III replacements.
This is NOT a guess. The stock injectors are well known to be junk and a car that sat for years.....its a guarantee.
Go thru the fuel system tank to intake. Rebuilt the regulator. REPLACE ALL 8 Injectors,.
it'll run,. that's a promise !
Good luck !