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Replacing Injectors --- tips

Wade Nelson

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If you'll search on "injectors" you'll find several excellent threads and pictoral how-to's on this site, including:


I just got done doing the job, and would like to offer a couple of tips to anyone planning to do this.

First of all, the job took a serious six hours, even with air tools with only 1-2 very minor screwups. Taking pictures along the way repeatedly "saved" me lots of heartache.

Plan on replacing innumerable vacuum lines / emissions hoses that are baked and aren't going to come off their nipples easily, unless you've already replaced them all. I discovered a crack on the BOTTOM of my hard-as-a-rock PCV line that had clearly been allowing faux air to enter the manifold. Since it's a molded line, and it was Sunday, I didn't have many options there.

(Has anyone found any of these for the ZX in stock anywhere -- L-shaped with a wave at the end...the one I bought on ebay didn't fit...for earlier model, apparently...)

Removing all the err, ahh "important stuff" will give you access to some hoses you couldn't or probably wouldn't otherwise replace, like the tiny 7/64" hoses on the thermoswitch buried beneath/beside the Aux Air valve. So stock up on rubber fuel / emissions hose before you begin -- 1/4, 5/16, 7/64.

Cutting the 5/16" fuel line to the cold start injector right in the middle is BY FAR the easiest way to disconnect the fuel rail without otherwise breaking the plastic nipple on the $79 piece.

Be sure and label your injector connectors along with your Aux Air Valve and Cold Start Injector connectors before removal, since they're identical...

Unless they're all in pristine condition, I would HIGHLY recommend going ahead and buying NEW injector connectors (electrical) off eBay before you begin. Most of mine were brittle, already cracked, and some were already missing the retaining clip.


Next, BEFORE you remove the old injectors, notice what position (on the clock dial) the electrical connectors are FACING, so you can install the new ones facing the same direction. This will minimize the wrestling you have to do with the old, stiff wires & rubber boots on them, esp #3, which is buried beneath the FP regulator.

One of my injector pedestals / holders was cracked. Usable, but I sure wish I'd had a spare or two in hand before discovering it on a Sunday afternoon. (things your mechanic will never tell you --- yeah, I just re-installed it and hoped for the best...)


I used an impact wrench, with a #1 phillips bit, to remove the injector hold-down screws, on a very low torque setting. There simply IS NOT ROOM for an 8mm, even a thin-wall deep socket, on many of these. Poor design, but fortunately none of mine stripped out. You might be able to get an 8mm open-ended in there, on SOME, to crack them loose, but some will just prove impossible to reach.

I loosened all the injectors and took them out still attached to the rail. I then used a hose cutter to sever their attaching hoses right in the middle, and THEN removed the clamps & rubber from the barbs on the rail. I used a boxcutter to slit the hoses before attempting to twist and fight them off the barbs.

A little grease on the barbs, which gasoline will dissolve, makes re-installing the rail about 1000% easier. Avoid Sil-Glide or other silicone lubes which can "kill" your 02 sensor.

The rubber seals on my old injectors were baked SO HARD that they couldn't be cut off, to remove the hold-down flanges for re-use on the new injectors. I had to hold them up to my grinder and grind off the old, hard rubber. Tip: Wear leather gloves. Why? *observe Band-aid on index finger...*

See picture....

Wire-wheeling the flanges can make them look a lot nicer before re-installation. Wish I'd had a spare set to get cadmium plated before I began....if it were a restoration job...

Install the small seals ONTO the tips of the injectors BEFORE mounting them. Do NOT install them in the holes in the manifold and then try and slide the injectors through them.

I ended up with an EXTRA set of injector seals (six large six small) if anyone needs a set. $15 plus shipping....

This is where you need to rotate the new injectors to match the direction the electrical connectors were on the old ones before tightening them down.

Since these are rubber seals, I tightened them down, waited 30 minutes, then went around and hit 'em all again to make sure the rubber was properly compressed.

I had to TRIM the hoses on the new injectors to 1 7/8". The old ones measured 1 3/4, but I'd rather cut twice so I went 1/8 long....just in case.

Folks, be SURE and put fuel injection clamps around the rubber hoses BEFORE you fit the rail back on. I only got five out of six so I had to settle for a screw clamp on the one this bonehead missed. I'll be reminded of this mistake forever, every time I look under the hood from now on...

Overall the job was a fight from beginning to end. Every single component possible is in the way and has to be removed. There are lots of bolts passing through TWO tabs before screwing into the block, and getting 'em both to line up (and not strip the bolt) was a PITA.

(A better design is when they give you bolts with an unthreaded TIP that makes starting a lot easier)

When I fired it up it cranked forever, and ran quite poorly. I had used lots of engine degreaser and a garden hose to clean off the galley, and perhaps it ingested some of that. The next morning it, after going around, re-checking EVERY hose clamp, it started right up and ran a lot better, although the idle was NOTICEABLY lower and still feels a little rougher than before. I attribute this to the now-sealed PCV air leak, but I'm not 100% convinced I'm at 100% yet...

The "galley" has several drain holes that let water escape. If any don't drain, you probably want to poke a wire through them...

Disconnecting the battery and forcing the ECM to "re-learn" its adaption is probably a good idea, I just haven't done it yet....

I had a friend holding a fire estinguisher standing by when I cranked it, JUST IN CASE I'd missed tightening any fuel hose clamps, including the one on the cold start injector I'd replaced as well. Leaking fuel hoses spraying fuel at 30psi can get exciting REAL fast...

I can't say this was a fun or easy job. I wouldn't recommend it unless you've got all the possible parts you might in hand, tools-a-plenty, and a fair bit of wrenching experience under your belt. I was absolutely exhausted by the time I was done.

I can already detect an improved throttle response, but there wasn't any big jump in horsepower, engine smoothness, or anything else. She DOES seem to catch (and start) when I crank it noticeably faster.

Hope this helps the next guy...



Edited by Wade Nelson
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Ok, so here's the story on the rough running after injector replacement, and how it got diagnosed.

If you just want the short version, it was the wires to one of the injector connectors.

I had come up with a mental list of a number of possibilities.

One, the cracked pedestal I was forced to re-use was leaking air.

Two, I had perhaps forgotten to put one of the tip seals on one of the injectors, and it was...leaking air.

Third, some vacuum hose somewhere, or the once-repaired PCV hose, was once again....leaking air.

The idle was lopey, and to ME, it sounded like a vacuum leak. My mechanic friend Ed immediately said, "Hmm, sounds like an ignition misfire. I'd check the basics..."

Since he's got about 50X as much experience as I do, I listened to him instead of arguing for a vacuum leak.

Other clues: Runs well above idle, didn't feel like I was only running on 5 cylinders, yet fuel mileage seems to have dropped considerably. Something that is VOLTAGE related, like a fouled plug, will often run better at higher speeds when there's enough voltage to arc through the crud.

So I checked the cap & wires, which I had removed to do the job. Everything looked nominal.

Pulled the spark plugs. #1 was heavily carbon fouled. All the others looked OK.

This kinda pointed to the Cold Start Valve / Auxiliary Air Relay connectors possibly being swapped, as the CSV is closest to cylinder #1. But connecting / disconnecting neither improved matters. (I need to get in the FSM and check the wire colors, and grab the meter and check proper operation, but that's for a later day...)

So Ed grabs a can of brake cleaner, and sprays ALL AROUND the injectors, and pedestals. There is no increase in RPM from the addition of faux fuel. So it's probably NOT an air leak, at least not at any of the injectors. Whew!

About this time Keith, the service writer walks over, and can't help himself but get involved, LOL. He pulls the hose on and off the fuel pressure regulator, and engine rpm responds as expected.

Next he starts playing with the first three injector connectors, (all three of which are broken and no longer sport a retaining clip) and voila! Wiggling #1 causes the miss to disappear. Using contact cleaner on it, and a pick to tighten the pins doesn't fix it though. We deduce the wire is cracked slightly upstream of the connector itself, and held at just the right angle it makes a connection. AND, as noticed earlier, at higher RPM's where the voltage simply jumps the gap.

Instead of a stethoscope, Keith grabs a 2 foot screwdriver, holds it to his ear, and can HEAR the injector cutting in and out as he wiggles the wires, comparing the sound to #2.

So replacing those connectors is a real good idea when you go to replace injectors.

And hopefully these quick diagnostic steps will help anyone else with an injector miss.

I was tired, had kind of reached the end of my patience after replacing the injectors, and I really needed a fresh set of eyes to figure out the problem. That's when it's good to have friends in the business. They'll find a cold six pack in their fridge at 5:00

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  • 2 weeks later...

Here's more info. One of my six new injectors failed, first fouling plug #1 (and giving me HORRIBLE gas mileage) then sticking open and hydrolocking the motor.

One "symptom" was at idle, the exhaust note sounded funny, even though there was no engine miss. It was like it went pop pop pop in time with one cylinder firing, due to all the extra fuel in the exhaust.

Hopefully no head/gasket damage was done, I'll find out pretty soon here.

When I removed the fuel rail AND injectors I could see #1 going drip, drip, drip.

I removed the #1 injector and sprayed it out with brake cleaner onto a fresh paper towel. The ONLY thing that came out was the tiniest sliver of rubber. Apparently while installing the injector hose onto the fuel rail, it "shaved" a tiny bit of rubber off the hose, despite my use of lube. Or else that bit had been floating around in the fuel rail ever since some other hose or fuel filter replacement.

I tried "clicking" the injector using a spare resistor pack, and connecting it to the battery. It wouldn't click. Neither would my OLD cold start valve. In contrast, one of the OLD injectors happily clicked. So there must be a second bit of schmutz actually clogging the pintle.

Next I'll try using compressed air to blow out the failed injector from the nozzle end, and try to re-click it.

This time I went ahead and replaced broken injector connectors, and replaced the three hoses on the thermoswitch accessible only once the fuel rail is removed. All were hard as rock, of course. By first cutting them in two, and THEN slitting them lengthwise, I managed to remove them from the plastic nipples on the thermoswitch without breaking any of THOSE off. Hurrah!

I also replaced the injector pedestal that was broken, for which I previously didn't have a replacement. Except now there were TWO broken ones. good thing I grabbed THREE at the junkyard.

Right now the hood is up, and I"m waiting for FedX to show up with my replacment injector. I've already cleaned everythign under the hood I can find to clean, so....

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  • 1 month later...

Well problems with injectors usually starts with misfiring, or having a hard start or hesitation. Listen for sounds but if there are other sounds it might not only be the injector. Check for engine crank. You said that there are leakage, it could be a dangerous thing because fuel leaks from your injector can cause a burn in your vehicle's engine. If there are leakage it must be replaced immediately.You could try visiting autopartswarehouse.com (lots of new carparts here) for replacement. Just note that before you test the equipment-- fuel injection system, you must relieve the fuel pressure by having the vacuum hose disconnected from the fuel pressure regulator and remove the fuel tank cap. Hope this helps. Thanks!

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Just note that before you test the equipment-- fuel injection system, you must relieve the fuel pressure by having the vacuum hose disconnected from the fuel pressure regulator and remove the fuel tank cap. Hope this helps. Thanks!
That may help something though I'm not sure what but it won't relieve the fuel pressure.
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