Fuel Injector Replacement

I am considering replacing the fuel injectors in the 2.9L in my 87 B2. Mostly because so much of the engine has been replaced yet these are still the original. Had the question been brought up when other work was being done I would have just had them replaced rather than put old ones in.

While the engine basically runs okay, the fuel economy has been really low (18mpg with manual trans when I've always gotten slightly over 22mpg). While I tend to think the fuel economy issue isn't related to the injectors, I don't like having these old injectors of unknown condition in what is otherwise new.

So my question is, other than basically putting in an OEM replacement, is there any direct fit replacement injectors I might be considering? For example, on the Jeep we have there is injector with four jets available to replace the stock which has just one.

I would stick with the stock injectors. Over time the parts do wear out, and the mesh socks in the injector heads actually bung up with crud. It's possible the pintel valve (never could spell that thing right) could also have a layer of varnish that can cause it to seep out and not give a correct spray pattern. You want a fine mist of fuel with the injector 'fires'..and not a drippy mess.

If you want an idea of how good or bad the system is working? Read up on how to use a fuel pressure gauge and install one on the engine. Start it up and let the system go stable---Then shut the engine off and watch the gauge. If the needle nose-dives quick? High bet one or more of the injectors is weeping.

When I did the injectors on ours? I replaced 2 and serviced 4. I actually pulled the rail and kicked the ignition 'on' to prime the fuel system. From there I just put a rag under the injectors and watched. The ones that where bleeding badly? Replaced. The ones just starting to weep? New fuel mesh socks and cleaned them with carb spray and a clever modified power supply I used to fire the injector wide open. So far it's lasted 2 years. It's starting to get bad again, so I'll have to replace soon.

In my opinion? Putting in larger fuel injectors or 'aftermarket' performance injectors on these older engines is a waste of time and money. These are not race car engines and never where intended to be such. Put another way: 16 to 1 is the nominal ratio for air/fuel. To much one way or the other will either waste fuel or run like crap. Your onboard computer reads the sensors and does it's best to maintain that. Putting a (as example only) 16lb injector in an 10lb application? The computer will reduce the duty cycle accordingly and you'll have the same results.

If that was in a high performance engine that needed that additional capacity to keep up? Sure, go for it!

S-

Tedybear said:

Over time the parts do wear out, and the mesh socks in the injector heads actually bung up with crud. It's possible the pintel valve (never could spell that thing right) could also have a layer of varnish that can cause it to seep out and not give a correct spray pattern.

Click to expand...

When you say "seep" do you mean that even when the valve is closed some fuel seeps thru the valve, not just a bad spray pattern? I guess that is the point of fuel pressure test.

If I understood correctly I wasn't aware that is a potential issue. I'll certainly do that pressure test. Can you clarify what "nose dives quick" verses normal would be? This sounds like a great idea.

Seeping would certainly explain the low fuel economy and could explain how she starts great when she has been off for either just a few seconds (like restarting after stalling) of off for a an hour or so, but if I go into a store, when I come out she has to crank an few seconds before catching.

Well I won't get my hopes up...I am sure there are more than a few potential things that can cause these things.

Tedybear said:

In my opinion? Putting in larger fuel injectors or 'aftermarket' performance injectors on these older engines is a waste of time and money. These are not race car engines and never where intended to be such. Put another way: 16 to 1 is the nominal ratio for air/fuel. To much one way or the other will either waste fuel or run like crap. Your onboard computer reads the sensors and does it's best to maintain that. Putting a (as example only) 16lb injector in an 10lb application? The computer will reduce the duty cycle accordingly and you'll have the same results.

Click to expand...

I understand completely. I was not thinking larger or performance injectors that could deliver more fuel. I was thinking more along the lines of ones that might provide better atomization for more efficient burn thus potential for some better fuel economy. Of course that may be a diminishing returns sort of thing.

Thank you.

ab_slack said:

When you say "seep" do you mean that even when the valve is closed some fuel seeps thru the valve, not just a bad spray pattern? I guess that is the point of fuel pressure test.

If I understood correctly I wasn't aware that is a potential issue. I'll certainly do that pressure test. Can you clarify what "nose dives quick" verses normal would be? This sounds like a great idea.

Seeping would certainly explain the low fuel economy and could explain how she starts great when she has been off for either just a few seconds (like restarting after stalling) of off for a an hour or so, but if I go into a store, when I come out she has to crank an few seconds before catching.

Well I won't get my hopes up...I am sure there are more than a few potential things that can cause these things.



I understand completely. I was not thinking larger or performance injectors that could deliver more fuel. I was thinking more along the lines of ones that might provide better atomization for more efficient burn thus potential for some better fuel economy. Of course that may be a diminishing returns sort of thing.

Thank you.

Click to expand...

Better atomization might be, how to get this...Different makers may have a better track record then others. I'm sure everyone has seen the picture of the injector spraying on the can of cleaner at the local store. One looks pretty drippy and the other looks like a fuel mist in a fan pattern. That makes a huge difference. I think instead of looking for a performance injector in regards to the capacity, maybe looking for a performance one with a proven track record of quality.

I'm sure others will chime in with suggestions. I happen to use Bosch injectors. Just what came with it. Probably not even the factory ones LOL! (the ol' girl has over 200k on it)

In regards to the pressure test? All things being equal the system should hold pressure for a short while before bleeding off. Maybe about a minute before hitting zero? This one I'm not sure of. Ours was easy to figure out. The pressure tanked quick (under 10 seconds) and there was a bad smell of raw gas in the intake. I pulled the plenum off, removed carefully the injector rail itself. And put a rag under it. Just had the wife bump the key to 'on' to prime the system. (not starting it of course..that'd be a neat trick)

I viewed a lot of drips off a couple of the injectors, so I replaced them. Large drips can only be caused by crud on the tiny valve--which can also really screw up the mist fan patten you're looking for when it's installed and working. I would think very minor weeping is acceptable to a point. But if you see large droplets?

When I removed the injectors from the rail? I found severe rust in the rail, and the socks full of crud/rust. It's about due to be cleaned out again I'm sure. And don't bother with the valvoscream injector cleaning service--that one is all smoke and mirrors with a large price tag- There are better OTC (over the counter) cleaners that help with minor stuff.

S-

Thank you for all the information.

I performed the pressure test tonight and with ignition on it jumped up to 20 the first time. Starting the vehicle it went up to a bit over 30psi.

Bleed down was extremely slow so, at least that doesn't look like a problem. After 10 minutes or so it only had dropped a couple PSI.

Cycling the ignition back on (but not cranking) it jumped up to 40psi. After starting the engine it dropped to 30 PSI.

I released the pressure and repeated turning on the ignition without cranking the engine and it went up to 30psi. Again after starting it was at 30psi.

I don't know off hand if those are good pressure numbers. As far as injectors leaking and letting the pressure bleed down, that doesn't seem to be an issue.

any tips on cleaning the injector? is replacing the plastic caps on the nozzle necessary

Not my work , just a good how to.

What you need:
1.) Spare injector wire and 12volt battery or power source
2.) container and chem to soak in
3.) #8-10 screw (?) tool
4.) air compressor w/rubber tipped blow gun tool
5.) RJM kit (RJM Injection Tech — Fuel Injector Service Kit)

Optional:
6.) Spare injector set from junk yard
(This is only b/c it will take a couple days to get this done so your truck will be out of service- spare set of injectors reduces your trucks down time) I pulled 2 spare sets and paid $1 each for them ($16).

Step #1: Strip Your Injectors
pull off the o-rings and plastic parts including the mini basket filters included in the RJM rebuild kit. You can see the front injector is stripped (cool whip container is what i used to soak them in)

Use a #8 screw (i think- you may want to double check) to remove the mini filter basket from the top of the injector. Just screw into the basket and pull out... Don't worry the RJM kit has new mini basket filters to replace the old ones you're pulling out.

Step #2: Soak
Drop all your injectors into a container of GOOD full strength injector cleaner. I use Berryman's B-12 Chemtool. Do not use cheap $2 store brand injector cleaner... It's not strong enough to break down the varnish deposits! You get what you pay for! Make sure your soaking container has a lid to keep evaporation of chem to a minimum, and to keep the wife from squaking about the smell (ie cool whip container - Or a 1gal can of Berryman's chem dip for $20 works good to). I usually leave them to soak a good 2 days at least... remember the can will say 20 mins but your trying to break down 20+ years of varnish buildup! This couple days of down time is the reason I suggest pulling a spare set of injectors from the JY...

Step #3: Open and Blow

You need to use the spare injector wire hooked to 6-9 volt power source (ie: motorcycle battery or 9v fire alarm battery) to "open" the injector. !WARNING! Keeping a constant 12volt source (ie: car battery) to the injector will ruin IT!!!! (via: Subford's later comment). Remember a injector is just a electrical on-off valve for gas flow... Not shown but I used the clamps off an old car battery charger and wired them to the injector wires. Either way hook wires to your power source, and snap the clip onto injector to send power to open the internal valve (you need to keep constant power to the injector to keep it open. (I'll cut a injector apart to show internals if you guys want me too...)
Click the image to open in full size.

Now that you have the injector you want to blow compressed air backward through the injector to push and blow all the varnish out. You'll be surprised what actaully comes out some times if you hold a shop towel to the other end to catch the air blown out. Press the rubber tip of the blow tool to the injector like this...


Step #4: Repeat Soak, Open, Blow
If you want to and have the time, you can repeat the soaking proceedure and blowing out proceedure to make sure your extra clean... enough said.

Step #5: Reassemble the Injector
Honestly if you can't figure out what to do with the kit pictured below after doing all of the above... well you should be slapped silly! This should be self explanatory...


Step #0: Ask questions
This is step "0" because you should ask questions first so you don't screw anything up... How hard is this??? Well this is like a 3 (on a 1-10 scale). Or about a 2 beer job for those of you who count beers while doing their truck work.