What 'upgrade' Fuel Injectors Do I Purchase? '92 4.0L

[Rohls]

Alright…a bit of an update...

 

I installed the above injectors…truck ran like crap…sputtered, coughed…etc. misfired.

I called the ebay seller, he calmed me down and was very polite, said he'd replace them if I was satisfied. 

 

I took them out tonight, clean em a little, put them back to how the seller recommended and fired er up…SAME RESULT: sputter, cough…ROUGH idle, ran like crap. Tested it down the road, no power, misfire etc….sigh….

 

Maybe I buggered something else up?

 

I put the stock injectors in…fired right up, perfect idle everything is fine...

 

SO--do I have a faulty injector? Seems like the motor was getting WAAAY too much full. Also, the pressure at the rail (relief valve) was nonexistent (!) for the rebuilt injectors….strange…I think I have a faulty injector…like one is stuck on or open.

 

Is there anything else one needs to do to this mod? Fuel pump upgrade…? I thought this was plug and play…:/

 

Thoughts?

 

My next plan is to get a different set of injectors and throw those in...

 

good thing I'm getting really good at this..:)

 

Thanks!

[HOrnbrod]

Obviously you never bothered to check (or clear) the fault codes.

[gogmorgo]

If you can turn your key back and forth in the ignition, count as high as nine, and remember that number at least long enough to write it down, you should be able to check your codes by yourself in under a minute, depending on how many codes you have. The only required tool is your ignition key. No scan tools necessary.

Here's the link again if you need it. http://comancheclub.com/topic/28111-reading-obdi-91-and-92-mj-fault-codes/

[Rohls]

Thanks for the help.

 

After some cursing...

 

I took the refurbished injectors out, arranged as recommended by the seller, put back in...no go..Same crap.

 

I stuck the original injectors in and she fired right up....I'm leaving those in for the time being.

 

I got a another set of refurbished injectors I'm going to slap in there as soon as they arrive....TBD

 

!!

[Rohls]

Obviously you never bothered to check (or clear) the fault codes.

...I cleared them.

[Rohls]

If you can turn your key back and forth in the ignition, count as high as nine, and remember that number at least long enough to write it down, you should be able to check your codes by yourself in under a minute, depending on how many codes you have. The only required tool is your ignition key. No scan tools necessary.

Here's the link again if you need it. http://comancheclub.com/topic/28111-reading-obdi-91-and-92-mj-fault-codes/

:thumbsup: . :MJ 1: .

[HOrnbrod]

 

Obviously you never bothered to check (or clear) the fault codes.

...I cleared them.

 

 

What fault codes were you reading?

 

Sometimes when you make a dramatic change in the A/F ratio or injector pulse width (like changing fuel injectors) or engine timing, the ECU must be forced flashed to clear it's residual memory tables. Disconnecting the battery cables will clear the fault codes, but does not erase stored or residual memory. This is the procedure:

 

Disconnect the POSITIVE battery Terminal and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the ECU capacitors, which maintain the Adaptive Memory).

 

Reconnect the Battery Cable

Turn Ignition Switch to the “On” position but DO NOT start the engine

Turn Headlight “On”

Turn Headlights “Off”

Turn Ignition Key “Off”

[Rohls]

 

 

Obviously you never bothered to check (or clear) the fault codes.

...I cleared them.

 

 

What fault codes were you reading?

 

Sometimes when you make a dramatic change in the A/F ratio or injector pulse width (like changing fuel injectors) or engine timing, the ECU must be forced flashed to clear it's residual memory tables. Disconnecting the battery cables will clear the fault codes, but does not erase stored or residual memory. This is the procedure:

 

Disconnect the POSITIVE battery Terminal and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the ECU capacitors, which maintain the Adaptive Memory).

 

Reconnect the Battery Cable

Turn Ignition Switch to the “On” position but DO NOT start the engine

Turn Headlight “On”

Turn Headlights “Off”

Turn Ignition Key “Off”

 

 

Thanks, I did this exactly. With the stock injectors back in, she runs great....though seems to be a LOT down on fuel economy...grrr...I'm gonna try to replace the O2 sensor and fuel filter...

[GHayduke]

After research, etc. I'm going to try upgrading my factory 98' 4.0 injectors to rebuilt Seimens XF2E / YF1E injectors (looks like 22.2 lbs/hr @ 43.5psi). I'll report back how they work out.  I was very tempted to go grab boneyard injectors, but would feel like I need to rebuild them before use.  I found 6 rebuilts for $90 with connector adapters and a two year warrentee.... We'll see.

[GHayduke]

So far the injectors are working fine.  I have not had a chance to check mileage yet as I've been hauling a lot of stuff around...

[GHayduke]

Still happy with the injectors but sometimes there is some hesitation at start-up rather than just immediately starting.

[Rohls]

 

I recently installed a fuel pressure gauge (dial filled with glycerin \) ontot the fuel rail in my 92 4.0 MJ.

 

The fuel pressure at idle is 44PSI, at ~2000 rpm it jumps to 49 PSI...I have the FORD 19# and the Chrysler FPR.

 

Is this normal pressure wise?

 

I have been experiencing hard starting when HOT and easy starting when cold...consistently.

 

Any ideas?

 

Thanks!

[Rohls]

 

 

Still happy with the injectors but sometimes there is some hesitation at start-up rather than just immediately starting.

I'm thinking of switching to these injectors. What kind of hesitation do you notice? Any comment on fuel consumption?

[Eagle]

I've been trying to stay out of this topic but, since it is now deteriorating, I'll just chime in with the official Olde Pharte's pouint of view, which is:

 

WHY does anyone think that larger injectors are in any way an "upgrade"? The factory engineers size the injectors as they do for a reason (probably more than one reason). True, they are designing for the "average" range of drivers and driving conditions, but most of us never exceed those parameters anyway.

 

How could the factory injectors NOT provide enough fuel flow, in anything other than a full race engine on a track? The smallest factory injectors were the Renix injectors ('87 - '90), which were rated (IIRC) for 19.2 pounds per hour. That's PER INJECTOR. So if you were to find a way to run those injectors to wide open and 100% duty cycle, each injector would provide 19.2 pounds of fuel per hour.

 

The 4.0L is a 4-cycle engine, so for each revolution there are three intake events and three exhaust events. At 5,000 RPM, which is the practical redline for the 4.0L engine, in one minute we have 15,000 injector squirts. In one hour, we have 15,000 x 60 squirts, which is 900,000 squirts. If EACH injector can provide 19.2 pounds per hour, and there are six injectors working, that means a theoretical 115.2 pounds of fuel per hour.

 

Gasoline has a density of approximately 6 pounds per gallon. 115.2 divided by 6 is 19.2 gallons per hour. In rough terms, that means an entire tank of gas every hour. Does ANYONE use anywhere near that much gas?

 

Let's say you cruise at 75 MPH and get 15 MPG. 75 MPH means in one hour you travel 75 miles, and at 15 MPG that means in that hour you burn 5 gallons of gas, or 30 pounds of fuel per hour. There are six injectors working, so each injector only has to flow 5 pounds per hour. If they are rated to flow 19.2 pounds per hour -- I think there's enough "overhead" flow capacity to handle those short intervals where you accelerate to 4,000 or 4,500 RPM as you go through the gears.

 

I dunno. I'm simply puzzled. A number of years ago a professional drag racer named Bob Salemi (an early member of NAXJA) built a pro race Comanche with a very modified engine. When he put it on the dyno for pre-season testing, it ran like crap. He tried (almost) everything, and it kept running like crap. Finally, the dyno guy checked the air-fuel mixture and suggested SMALLER injectors. BINGO! That was the answer.

 

Remember: "If it ain't broke, don't fix it."

[HOrnbrod]

Agree with most of that. While my Hesco stroker engine is a far cry from Bob's race engine, I can relate a similar experience regarding injectors. The Hesco crate engine came with stock 96-99 Mopar 53030778 "Gray Top" single hole injectors rated at 23.2lb/hr @49psi and an adjustable FPR. After doing a lot of exhaust and intake work and giving the ECU plenty of time to learn the new settings, I played with various fuel pressures dialing in the correct AFR for weeks and thought I had it perfect.

 

To be sure I went back to Hesco for a dyno run. Lee Hurley, the guy who developed FI for the AMC I6 did the dyno run. It turned out the best peak HP/Torque readings over the RPM range were developed at 43psi. Every engine is different, and you'll never know what works best until you do a dyno run. I sure noticed a hell of a difference on the way home.

 

I also asked him about the benefits of swapping to 4-nozzle Bosch injectors everyone thinks is an upgrade. He said he never saw any improvement for a stroker engine using these injectors on the dyno, and in a lot of cases produced lower numbers than the single jet injectors. Maybe it's different for N/A engines, I don't know. I do have a new set of Bosch 702 "Neon" injectors ready to go on, but not until the Mopar injectors break or leak. Then I'll have another dyno run.............