Injector & runner re-install

[Qdog]

Deep into the plenum job, so far so good. Do the big rubber rings that seal the injectors to the intake runners need to be replaced ? They seem hard but not brittle. The runners all have an oily build-up around the top, is this normal ? I expected them to be clean due to the fuel wash. Can the valley hoses really be replaced with all the lower runners in place ? It looks like taking out the middle four runners would greatly improve the access. I've read opposing opinions about replacing or re-using the runner to head gaskets, what is the right answer ? 4 injectors are out of spec (one completely dead, that explains the miss), anyone have 4 good injectors you don't need ? Thanks for the help.

[Q451990]

I'm going to come down in the don't mess with the runners camp... as far as hoses, they can be replaced without pulling the runners - but I asked the same question when I had to replce them. If you're comfortable with the added expense of replacing the gasket, go ahead and remove them, but I wouldn't re-use the gasket! Also, I'd go ahead and replace the rubber rings you mentioned earlier.

Heath

[forecast]

The hoses can all be replaced with the runners in place. (with a just a little nashing of teeth)

I believe you can re-use the Plenum to runner rings.

However ... just as I hope you're taking the chance to scrub out the plenum (or getting it jet washed at a machine shop) if you pull the runners you could get them scrubbed really well too.

The runner / head gasket is a thin sheet of metal, it could be reused, but no one who makes a living by serviceing automobiles will recommend it. I think I would go ahead and pull the runners. It will speed up the hose replacement AND let me clean them really well.

[Q451990]

How much are the runner gaskets? I agree it would make it much easier to work and good for cleaning! I priced them in the late 90s at over $100 each if I remember correctly, but it's been a long time and that was locally... The benefits of easy hose replacement and cleaning would be nice! I think those gaskets are like the ones on the EGR valve, so it's not entirely metal - has some other stuff on there too...

Heath

[DAEDALUS]

I just spoke to Justin at Scottsdale...the runner gaskets are $55.14 each. He said the '90 only needs 2 of them, but I *thought* each head had 2 gaskets each for a total of 4 (???). Maybe they've been redesigned? Off Scottsdale's website they have a "engine gasket kit" IIRC that's about $300 and which I think includes those, along with a bunch of other gaskets (plenum, head, TB, EGR). Verify with them though if you're thinking of ordering.

[forecast]

The gaskets are entirely sheet metal. They do have some ridges stamped into them. Shinny blue. There's just one per head.

Check with a felpro gasket dealer, that might be less than the dealer price.

[DougQ45]

QDog: I have 4 spare injectors for 1st gen Q that were cleaned and flow tested at a shop here in So. Cal. They look almost new, and are in little plastic bags. Comes with the 2 new O rings. Email me for digital pics. Doug

[Qdog]

Got to the knock sensors, they test at 562 & 569K, but each has a small crack. Should I re-install them, seal the crack (permatex ?)or replace ? Original, I think, with 160K miles. Not that I would, but couldn't one replace a bad knock sensor with a 550K resistor and live dangerously, but fool the ECU ?

[forecast]

Got to the knock sensors, they test at 562 & 569K, but each has a small crack. Should I re-install them, seal the crack (permatex ?)or replace ? Original, I think, with 160K miles. Not that I would, but couldn't one replace a bad knock sensor with a 550K resistor and live dangerously, but fool the ECU ?

Replace it if it's cracked. Even if it ohm's okay, it won't work right and will likely be intermitant - sometimes it will be open and then ECU will go failsafe for the next 50 starts.

Change them unless and only unless the cost will be a severe hardship. Basically then you'll be trading drivability, performance and possibly gas mileage for the $300 you didn't spend on the sensors. I predict that if you don't change them, in about 6 weeks you'll have a gnawing sense that you'll wish you had.

[Qdog]

I had to press out the injectors. Can they really be pulled out from the top without breaking something ? The dealer did the previous injector replacements. Either they used no lube on the O rings or it is long gone. What about using a silicone spray on the O rings to re-install ? I'm worried that I will break the tops of the injectors if I try to remove them with the fuel rail in the car.

[DAEDALUS]

I think if you pry the injector up high enough, you can grab it's body and pull it out without breaking anything, though you will scratch it up a little. I made the mistake of grabbing the little metal stem (pintle?). It came right out. Luckily that injector was bad already.

[Dinkydow]

Qdog/ I am just curious, what type of fuel do you burn? I mean are you burning nonoxygenated or just premium?? How often have you had injector problems, or is this your first?? I live about 350 north of you and was wondering mostly if you have been using nonoxygenated fuel?? Wayne

[Qdog]

Wayne, I've noticed that when I go to northern Minnesota the pump fuel is all rated 91 octane for premium ethanol blend. In the Twin Cities, I always use Holiday premium ethanol blend rated at 93. The Q runs just fine on the 93, much better than the 91 in the north. I've wondered why the difference between the regions. I like the Holiday gas, it is advertised as low sulphur. Pure gasoline is hard to come by anywhere in this state, and it's only legal for older cars, and about .50 a gallon more when I've seen it. I think the non-blended fuel is often leaded, anyway.This is the first time I've had to replace injectors (at 160K), but all my injectors have been replaced at least once by the previous owner between 40 & 80K. Where can I get 93 octane unleaded between Duluth & Grand Marais that has reliably clean gas ? I wonder if there is such a thing as a gas quality rating service for stations across the country. It would be great to know where to go to fill up with clean gas wherever you are.

[Dinkydow]

Qdog, I got a listing from the MHRA (Minnesota Hot Rod Assoc), If you would like a list of a few stations I would be happy to send them to you. I always go to where ever it is nonoxygenated, I kept close tabs on it and I do get 2 more miles per gallon and have less to fear with the injectors. The Amoco in Two Harbors has it, the Super America in Grand Marais, there is a Sinclair in Forest Lake, and many more along the route, also in the metro area, where about are you located?? Personally I wouldn't use anything but, In my experience the price has been very competitive because the stations are usally next to those who don't offer it. Wayne

[Qdog]

Thanks for the info, Wayne. I'm in the SW corner of Mpls, near Edina. I've never tried non-ox fuel in the Q, didn't really know it was available. On the subject of lubricating the injector O rings, I'm going to use a silicone based assembly grease, rated for 400 degrees. I think this will hold up the best. Another bit of advice for you plenum virgins (or near virgins, like me). I'm finding applications for standard flexible hose in place of some of the (expensive) Infiniti moulded pieces. The heater hoses for one (two), can be replaced with four short moulded 90 degree bends, coupled with short brass fittings to standard heater hose. Beats $74 for a one piece molded. Infiniti parts wants $35 each for two moulded hoses that connect to the rear of the cam covers. Since they didn't include them with my hose order, I'll try a flexible hose to see if it will work there.