Oil Pressure Problem-1990 Q45 replacement engine

[Q45denver]

I posted this on the Infiniti forum but thought I'd post it here as well-couldn't hurt.

zerothread?id=110508

[NISTECH]

I read through your post in infiniti, near the end it begins to make absolutly no sence. fisically it is impossible for that engine to have high[quite high] oil pressure at idle yet under accel, higher rpm, it drops below the idle pressure to the point it turns the light on. This is physically impossible, if anything your high rpm pressure should exceed 100psi with that kind of idle reading. Keep in mind I do not do alot of work on the Q since I am in the nissan dealer but on a max during cold start up the pressure exceeds 100psi on a gauge. I would assume the Q on could start up would have similar readings. I would really like to know what kind of pressure this car has on a stone cold start. The fact this infinit tech supposed master forced a tester into a whole it was not meant to be in gives me chills and makes me lean toward telling you to find yourself a more competant Tech.

[Q45denver]

Thanks for the information. The shop that i'm using says that the pressure spikes at 40 PSI at startup and quickly drops to 30. They suspect that it would drop even further as the engine heats up. I'm about ready to have towed to the dealer but the tech claims he has consulted with his tech friends at the dealership and they have never encountered a similiar problem either. I have not driven the car in over a month so some of the details are a little foggy. All I had to go on when driving it was the oil light and the noise. The oil light did not come on until operating temp was reached and the HLA did not quiet down until operating temp was reached. The shop attached a mechanical Snap-On gauge in lieu of the sensor after I towed the car back to them a month ago and found no oil pressure. I am in the process of installing an electronic gauge permanently which is how I found out about the thread. Apparently there is not enough difference in the thread count that the NPT fitting had to be forced in. Is there some kind of sealant that I could use on the sensor threads that would not effect the ground to the sensor? They said their gauge only screwed in part way so the thread further back may be ok.

About a month ago when they tested it there was no oil pressure at any RPM up to about 2500 RPM. The idle pressure improved to about 30 PSI about a week ago for some unknown reason (see my post 4/6/05) after the shop changed the oil and filter and now the HLA is no longer noisy but pressure still does not go up when revving the engine and actually seems to drop off. Their current readings show no more than about 30 PSI at any RPM except for that initial spike when they start the engine when it goes to about 40 PSI. That about where they left it. They don't believe that a motor flush will do anything. I plan to look at it Friday and will get more specific readings at various operating temps. I guess the next step would be to pull the pan again and check the bearing clearances and see if there are any damaged seals or o-rings. The initial tests indicate that the bearings and rings may be ok.

[NISTECH]

Question has any internal engine work to this car been performed?

[Q45denver]

Question has any internal engine work to this car been performed?

Don't know the history of this engine (third one for this car and maybe soon to be a fourth) but the guides had been replaced at some point. Supposedly it only had 50K miles. Is there a national tech support line that Infiniti or Nissan runs that could provide some help?

[NISTECH]

yes but the car would need to be in service with a work order to reffrence for repairs. The help desk is only for dealers.

[NISTECH]

btw my thinking about the engine work was if someone may have installed a bearing incorrectly this would make sence on the high idle oil pressure. but again the cold start reading should be through the roof.

[Q45denver]

The puzzler is the pressure seems to vary from day to day. The high idle reading may have had more to do with them not running the engine to operating temp for fear of further damaging the engine. I will try to get some readings at operating temp today. I'd like to take it to the dealer but already paid them for the installation of the engine and may be stuck with this shop for the time being. I think they do need to pull the pan and check the bearings before preceeding any further. Can't believe they haven't done this already since they had the pan off twice and knew there were oil pressure problems. Thanks

[Q45denver]

Just an update on the situation. I went to check on the car and get some pressure readings however, after running the engine to get it to operating temp it developed a rod knock so it looks like a writeoff. I wonder what the record it for the most engines in one car? Latter I went to look for engine number four at the local wrecker. All had rod knocks and the wrecking yard owner said it was very common in the Q45's.

[NISTECH]

Ouch. Is the engine rebuildable thats in it?

[Q45denver]

Probably not since it has no oil pressure. The last engine which is still at the shop was probably a better candidate in that it has good pressure but a severe rod knock. According to the experts, it is not practical to rebuild them due to high labor and parts and lack of expertise. Considering I could get a used engine for $750 or a new short block for double that, what would you recommend?

[NISTECH]

its a tough call. If I remember correctly the entire engine is all aluminum which makes cyl bore work a bit tougher and yes the cost is substantialy higher to rebuid verses used. Problem here though is your not finding a usable one. As a last resort you would have to build an engine, but if you can find a reliable used one definitly go that route.