Howdy folks. Got a question I was hoping I could get some help with.

95 XJ
5spd manual
4x4
2D
4.0 stroked to about 4.6
Stock head but refreshed with a 3 angle valve job and all new innards
Forged Pistons
stage 1 Clegg cam
6 hole, 24lb, 252cc injectors also from Clegg
stock intake/throttle body
banks header jet-hot coated
banks monster cat back 2.5in exhaust w/ new cat

runs very rich, backfiring on downshifts in 1st and 2nd
burned off the ceramic coating at the collector on the header.
Not near the power I expected but still torque-ie and fun to drive.


Ive added a cold air intake and that made a big difference but its still too rich. Still backfires. But, now Im thinking that I could go with a smaller injector and a hotter coil and plugs and may have a better effect. I could open up the throttle body and install the newer styl intake (i have one in may garage thats cleaned up and ready to install). My thinking is that If I go with a smaller injector instead, I can keep it from getting too snappy off the throttle and I wont have to swap the intake and modify my throttle body.

Here’s my dilemma, when installing the new injectors I could have used adapters since my system was an ODB1 and wired as an EV1 connector but the new injectors were EV6. So instead of using the adapters (that actually interfered with the throttle cable bracket) I converted the jeep over to EV6 connectors. Problem is, now, if I go with another injector, I dont want to rewire this thing again. In essence, Im not sure which injectors to use. I need injectors that are ev6 but will still fit into my fuel rail and preferably 6 holes and excellent atomization.

Suggestions?

 

I would suspect the injectors could be too large. Do you have the part number?

 

It's impossible to over injector an engine if the injectors are rated less than 1500cc. 3 Golden rules of hot rodding, Can never oversize fuel system, Can never oversize ignition system, Can never oversize push rods.

It is possible to undersize injectors. Actually it is probable. 24# injectors are tiny. Not nearly enough for a well built, well tuned Jeep/AMC stroker. You don't still have the stock fuel pump and computer do you? If so, you're actually running lean. Super hot exhaust, backfiring, lack of power = lean, not rich. You need a 255 LPH fuel pump, 30# injectors and you need to get that thing tuned. You cant put a larger than stock displacement engine into your vehicle with the stock fuel system and engine computer and expect it to make more than stock power. The stock injectors are capable of producing 24#/HR of fuel depending on line pressure. Whoever decided that 24# @43 PSI was a good match for a 4000 FPM piston speed 4.7L engine should be terminated.

 

I’m not exactly new to this but I have lots to learn all the same. That said, I am running stock a stock ignition system and a stock, in tank, fuel pump as well as a stock ECU/PCM or computer as you call it. Im unfamiliar with anyone that can edit or modify or tune an ODB1 system. That said, how would you proceed?


The issue im having that that it seems to be running very rich. Like I said, When I pull my foot off the throttle I’ll get some backfiring and the collector on the header has the ceramic coating burned off. It runs well enough that I’ve driven it coast to coast a few times now but if I’m driving it, especially on the highway, I get a better response if I gently roll on the throttle than if I just put my foot in it. If I just floor it, you can hear the engine want to bog down until it catches up. By installing the cold air intake, It really did make a noticeable improvement in performance and mileage. That helps convince me that its running pretty rich. So If Im running rich, then I’d like to take some fuel out of it. How do I do that? I get smaller injectors or a go back to a stock cam. Im not changing the cam so smaller injectors it is. I just want to use injectors that fit my fuel rail and have EV6 connectors. Im not sure where I might find that…

Again, If you have a better suggestion im all ears.

 

A stroker will run with stock ECU and slightly bigger injectors.
Which injectors do you currently have? The numbers are right on them.

 

Post pictures of the spark plugs before you do anything

The symptoms you've provided are those of running LEAN not rich. Or a leak somewhere, vacuum, intake, exhaust manifold. Rich is safe, lean is mean.

 

This^^

 

First off, I really appreciate you guys helping me out here.

Again, Im not the sharpest toot in the shed but I can still get the job done, sometimes.

Here is another reason that makes me think that its running rich. On the header, where the pipes turn down, the ceramic coating is fine, the way I understand it is that the extra, un-brunt fuel reignites in the collector, causing it to get exceedingly hot. If it was running lean the area on and around the down turn would be scorched as well, or so I thought.

So, lest say Im wrong and it is running too lean. Why does the performance improve with the cold air intake? Wouldn’t that cause the performance to be worse (more backfiring, through the tailpipe, less throttle response, running hotter)?

Again, if I am wrong, what do you suggest?

Ill go get a pic of the spark plug now.

 

You have a few good options. The least technical would be to install a wideband. This will give you real time AFR data.

You can install an obd1 to obd2 harness. You can read codes and live data (fuel trims) to see how much the ecu is adding or subtracting to the injector pulse. You can modify the ecu with hp tuners. Still need a wideband.

You can install a standalone and have full control over fuel and ignition. Still need a wideband.

X2 what is the injector part number?

 

Injector #: 9L3E-FA

 

I have a video of me testing the atomization of the fuel that these injectors put out and its it not atomized at all, it’s more like pulling the handle on a fully loaded garden hose. I tried to upload it but it was too large.

 

Well you can rule out a rich air fuel mixture. The porcelain would not be bright white like that if it was rich. The straps are also bright white, indicating a slightly lean mixture. So I'm thinking that your primary issue is more likely to be a leak.

You should put the shop vac (reverse orientation, blowing), up the tail pipe while spraying soapy water on all hot side sealing surfaces, as well as vacuum lines. See if you find any bubbles.

You also need a better ecu and you need to install a higher flowing fuel pump, and higher flowing injectors a some point.

 

For what its worth, here are the specs for my cam:

Specs:

• Duration 263 Intake | 267 Exhaust
• Duration @ 0.050 Valve Lift 209 Intake | 213 Exhaust
• Valve Lift 0.443 Intake | 0.443 Exhaust
• Lobe Seperation Angle 114 Degrees

 

It certainly isn't rich!!!
Cummins93 will be able to advise on those injectors.

 

Interesting. Perhaps faulty injectors.