Hey everyone. I'm getting ready to place an order for a replacement oil pump for my 86GT with a 3.4 PR that was freshly rebuilt by the previous owner. I've been getting some oil pressure issues, however no knocks in the car. I contacted the previous owner and it turns out a rod bearing went and that's why he got the car so cheap, then rebuilt it. He never bothered to replace the oil pump though so I'm wondering if something got in there and damaged it when the bearing went.

The sending unit on the car was a brand new 88 style one (although it died after a month on the car) The new sending unit should be in any day now and I had a shop hook up a mechanical gauge to see what was going on. They said it was running at 20psi idling and went down from there as the car warmed up.

Anyways on to the main question. What oil pump/pickup should I get to replace the old one? I'm thinking of going with a Melling one but have hear some conflicting things on which model to go. There was a post on here with pictures comparing the stock 3.4 pump to the Melling M95-HV. When I called up Melling though, they had no listing to use this pump for a 3.4... The Melling site suggest using the M134 pump and the 244S for the pickup. Any thoughts on this? I've read some horror stories of people revving Fieros with a HV pump and sucked their oil pans dry since it all went up top, blowing the engine. My gut feeling says just use the M134 but I'm totally inexperienced with stuff like this. Any help would be appreciated!

Stick with the M134 you don't really need the high volume one. You should be able to reuse the pickup tube.

Ok thanks! I think I'm going to grab a matching pickup tube too just in case. Previous owner had no clue if the pump was from a 2.8 or 3.4 and there must have been something that caused the rod bearing to go on an engine that supposedly has 70,000km's on it.

I used the M134 pump. I usually have around 25 psi idling, hot, right at 25K miles. While you have the pan off, plasti gauge that crank. Most of the time low oil pressure hot means loose clearance of the crankshaft bearings. Don't put it back in the car until you know.

[This message has been edited by josef644 (edited 06-26-2014).]

Yep! I have a semi-retired mechanic to help out with the oil pump. Going to check a few bearings, not sure if I should gauge them all or not. The previous owner that rebuilt the engine is a heavy equipment mechanic and said he followed articles here for the rebuild, so I'm hoping he did everything right apart from not replacing the pump when everything was out. Your post just reminded me of a few other things I've read here that I wouldn't mind getting cleared up.

-I saw a post somewhere on here that the oil pressure warning light goes on at 20psi. If so, don't people usually say 10psi/1000rpm? The car likes to idle ~800-1000rpm at idle so by that theory I can get down to 10psi without pulling the car over.

-What do you other guys usually idle at with a 3.4 PR? The only other mod that I'm aware of is a comp cam in the car.

-What is the proper connecting rod bearing clearance for a 3.4? The one thread I found here was pretty jumbled saying .008' then .08mm then .008" followed by someone saying 3.4's and 2.8's also use different bearing clearances.

Thanks for the help so far everyone!

I agree with Josef644 on both accounts. If your oil pressure is dropping that much after warm-up, chances are you have some loose tolerances in there somewhere.

Here are some bearing clearances (for the 3.4 V6) that I found online:

Main Bearings: 0.032 - 0.077mm (0.0013 - 0.0030")
Rod Bearings: 0.028 - 0.081mm (0.0011 - 0.0032")

Info was obtained from here: http://60degreev6.com/conte...-1%29-Specifications

Thanks for that 3.4 spec site, had no clue that existed!

So I finally got in the replacement sending unit from GM. I made sure it was an AC Delco part as everyone seems to say they read better. Turns out the dead one was some brand x one (died after less than two months in the car) and as it turns out never gave an accurate reading since day 1 (I'm assuming). Today was likely one of the hottest days we'll get here this summer and driving home with the new unit I had ~55psi cold idle and ~30psi hot idle.

Thing that's bothering me now is that the rad shop said I had 20psi cold idle and it went down from there which is even less than but somewhat consistent with what the old brand x unit showed. Wondering if they were trying to scam me into getting the oil pump changed for no reason... Still thinking I'll get someone different to do a mechanical test again or buy a guage myself just to be sure that the new unit is accurate.

Now to remember to see how the car starts with a warm engine with the new sending unit. It had low fuel pressure with car off/key on before, I'm wondering if the faulty sending unit was causing problems with the fuel pump.