Our '90 SE has started running rough and the check engine light has gone on. Mechanic says 2 injectors are dead; running on 4.

Is replacing the dead injectors a job I should be able to do myself? I've only done very minor engine work like replacing the distributor & rotor & spark plugs.

If so, how do I identify the dead injectors?


Thanks,

Greg

 

Hello could you start by telling us which injectors went bad (cylinder location)

 

Before doing that, why not try TC-W3? One of its benefits is lubricating injectors.....maybe it will bring yours back to life.

I had a lumpy idle on my honda and when I put TC-W3 in, the lumpiness disappeared.....so apparently one of my injectors was funky.

Check out the thread here;

http://forums.maxima.org/general-max...troke-oil.html

 

nissan injectors *almost always* fail electrically, not mechanically (by seizing or clogging). The wire coil degrades until the resistance is high that it doesn't draw enough amperage to operate the pintle. I've heard it's partly due to the corrosive nature of Ethanol-blend fuels (E10 being mandatory almost everywhere)

Easiest way to tell which ones is failed is to check the resistance on the 2 pins of the injector. For the front 3 (on a VG) there is a subharness with one positive wire (shared) and three negative wires (the other pin on each of the 3 injectors).

Top of page EC-148 http://www.nicoclub.com/FSM/Maxima/1994/ec.pdf

 

replacing injectors yourself is doable but sometimes a pain. You have to unhook the EGR tube which might require several days of pre-soak in PB blaster or other penetrating oil to get it loose enough.

You'll have to replace the upper and middle intake gaskets, so you'll need to scrape off the remnants (paper towel in the intake ports to prevent chunks from falling in)

you'll have to unhook a few coolant lines on the throttle body and intake manifold, so maybe drain a bit of coolant before you start.

you'll have to remove and replace the injectors themselves. I forget if the screws on the fuel rail are #2 size or not... but either way, be VERY careful and deliberate when removing them so you don't strip the heads.

Get a set of o-rings for the injectors if they don't come with injectors (depends if new or used), and use vaseline and a slight twisting motion to seat them in the buckets. If you tear or pinch the O-ring, you have to take it back out and do it again, cuz it won't hold pressure.

And might as well put new fuel lines on the rail and underhood, since you might have to chew up the ends of the hoses to get them off (plus they are probably just old). Fuel INJECTION hose (not just plain fuel hose) is needed for this due to the high pressure.

 

Oh yes, the good ole hunting around town trying to find a parts store not full of idiots trying to sell you vapor hose instead of fuel injection hose. I swear most of them will literally argue with you and truly believe YOU are the idiot and not them

 

Make sure the hose is labeled SAE 30R9.

 

Interesting..I did not know this. So your saying that guys who rebuild injectors are basically fixing the electrical part?

 

I don't think the rebuilders actually "fix" anything at all. we've never had good luck with "reman" injectors. I doubt they replace the coil, I think they just test them, and if they pass, clean them up to make them presentable. Keep in mind that when someone loses 2 injectors and replaces all 6 "to avoid doing the job twice" they are sending in 4 "good" injectors and 2 bad ones. So when you get those 4 "good" injectors they might already have significant mileage on them and fail a few years later. That's why they are 1/3 the price of new ones.

 

well think about it...it's a great business model...

your line blows up....sprays gas all over....your engine bay catches on fire.

you come back in next week buying a bunch o parts.

 

i think there is a PSI rating on the hose labels. like the fuel line (for carb'd engines) will be rated for 20psi, or something. and the other stuff obviously much higher.

 

The common feul line hose, like those on older cars with fuel injected carbuerators so to speak, have SAE30R7 rated hose. Their rating is around 200 PSI.


Proper multi-port fuel injection car need the strong stuff, SAE 30R9, rated at 900 PSI.

I imagine, but don;t know, that the new cars with direct injection need even stronger hoses.

 

is the stuff rated for way more than it'll ever see? using 900psi hose for a system that will only ever see 43psi? or do you get pressure spikes when you lift off the throttle from WOT?

 

Those numbers seem high for what I've commonly seen in existence and on cars. Most "fuel hose" idiots at parts stores try to sell you is rated for 40-60 PSI from what I've seen over the years. I always assumed this is what one would use on a carb system.

Then the EFI line I've seen is rated for ~200-300, which personally would be my acceptable level. I don't believe I've ever bought/used/sought out anything higher.

I guess I could be wrong but it would never even occur to me to seek out 900 psi hose.

 

when you lift it goes right back into the return...so i don't think it spikes.

the 900 PSI might be when the hose is new and under ideal conditions. under a few years use it might realistically be like 150 or something.

 

Well just for as long as it took for the FPR to react to the sudden change in conditions. Like when you slam a faucet shut, there is a brief spike in the water lines sometimes.

I guess it would depend on the ratio of injector flow vs return flow under WOT conditions... if return flow is always way higher even at WOT (ie, FPR valve mostly open even at WOT), then I guess the possibility for a surge would be almost 0 due to the FPR not having to make any kind of large adjustment. But if return reduces to a trickle under WOT (meaning the FPR would be almost totally shut) then I could see a pressure spike happening.

 

These are the specs i get from the OEM hose.

I would think that when you floor it to WOT, the feul pump jumps up in flow and the FPR may take second or 2 to regulate, that's when you'd you the greatest pressure differential in the feul line. I'm no expert, that's just my feeling.

 

i'm not aware of the fuel pump being a variable-speed device. It just pumps, and anything that isn't necessary to achieve the target fuel pressure just pushes its way out the FPR. Thus if the FPR was mostly closed (due to being at WOT) then suddenly reducing the fuel exiting the rail could briefly cause a pressure increase inside the rail until the FPR opens again (fuel still coming in, can't leave yet).... ASSUMING the FPR even has that much articulation at the relatively low flow rate of stock injectors at stock power levels.

The flow is: fuel pump -> rail/injectors -> FPR -> return to tank. Unlike some cars where the regulator is "before" the fuel rail, like a "returnless" system.

I have a fuel pressure gauge on my z, but it's not in running shape, and even if it was, the gauge sits under the hood so it's not possible to look at it while actually driving on the road. Maybe if I ever put it on a dyno, then I'd be able to look at it.

 

The pump creates the pressure and the FPR maintains it. An idling motor requires less flow than a motor at WOT, so the pump spins faster or slower depending on need....never constant.