Finally got the 4.7L running! HP Guess and injector?

[Rinkrat456]

http://www.jeepstrokers.com/forum/viewt ... f=5&t=4125 was my old thread. Long story short, either the cam was keyed wrong or the timing set was but we finally got that engine running. We had to degree the cam and forget all the recommendations we were given about timing cam and crank gear dot to dot or the 15 pin rule...my wife did all the leg work on the degreeing and the engine now fires over perfectly and has strong compression.

98 XJ 4 door AW4
Spark notes on engine build parts:
-'97 Cherokee NVH block & Head (block freshened up, bored 0.060 over, decked for almost 0 deck, new cam bearings installed.... head rebuilt with stock valves, new guides and new seals, stock springs)
-3214723 casting number stroker crankshaft from a '78, which makes this the heavy 12ctw long nose version and we cut off 10mm from the snout
-'97 long rods
-Icon 944 0.060" over Forged pistons
-1987-95 4.0L camshaft, Melling part number MC809 (adv duration 270in/270ex, duration @ 0.050 197in/197ex, lift .397"in/.397"ex, LSA 110/114, ICL 112)
-Napa high volume oil pump (massaged pan a bit to get it to fit)
-Stock '98 Cherokee injectors <problem child now
-Stock exhaust header, stock downpipe, cut off cat and OEM muffler for a straight pipe feeding into 4" round x 18" long Magnaflow muffler w/turn down
-Stock intake
-'98 ZJ 136 Amp alternator with smaller pulley

We have about 300 miles on the engine now and I have a strong feeling like we're running out of injector at about 50-60% throttle. As I increase engine load by stepping on the gas and holding it in gear there's a distinct point where I feel acceleration taper off substantially right before a very noticeable popping and sputtering event occurs and I back off the throttle. I've only done this twice to verify what was going on but this new engine has never been above that load amount as it won't take it.

With that said, and being a '98, the stock injectors read 53030778 and according to Dino Savva these are 23.2lb @ 49psi. If my injector math is correct, I believe I need 26-27lbers at 49psi. These are the EV1 injector connections and I have EV1 to EV6 injector adapters if need be from another project. I found a local speed shop who had 27lb Hemi injectors from a vehicle they boosted and were nice enough to just give me to try, unfortunately these were too short of an injector. Now I'm looking for something else that fits the Jeep fuel rail nicely.

Of all the injector calculators I've done the math on, I calculate a need for 27lb injectors for a 260-270hp 4.7L assuming an 80% injector duty cycle. I don't think that's outside of the bounds for this Jeep at the crankshaft.

Thoughts? Opinions or help with injector selection?

[Cheromaniac]

With that said, and being a '98, the stock injectors read 53030778 and according to Dino Savva these are 23.2lb @ 49psi.

That's me.
The stock injectors definitely won't cut the mustard and on a Jeep I6, the correct injector size seems to be the expected HP output divided by 10 in lb/hr. I think your engine will be making closer to 240hp rather than 260-270 (you have stock unported head and stock cam) so a set of Accel 24lb'ers (flow is 24.4lb/hr @ 44.1psi so at 49psi they'll flow 25.7lb/hr) together with your EV1 to EV6 adapters will give you enough fuel flow, and even allow you room to upgrade the exhaust to an aftermarket header with 2.5" downpipe without running lean.

[SilverXJ]

Congrats on getting it running! 24# injectors will work well.

[Rinkrat456]

I have a local friend with an extra set of 02 LS1 injectors. They have GM #12561462 on the side, which a google search comes up with the following data:

Test date: 8-21-05
Time: 15:30
Fluid Temperature: 69F
Barometric Press: 29.99
Relative Humidity: 53%
Altitude: 940ft above sea level

Remember:
1 bar = 14.503 psi
92 Octane tested at 0.745sg.
87 Octane tested at 0.725sg.
3 bar = 43.509 psi
4 bar = 58.012 psi

Injector #280 155 931 GM #12561462
60 Second static flow test @ 0.685sg @ 3Bar = 270mL divided by 10.5 = 25.714 Lb/hr
60 Second static flow test @ 0.685sg @ 4Bar = 315mL divided by 10.5 = 30.00 Lb/hr

60 Second static flow test @ 0.770sg @ 3Bar = 255mL divided by 10.5 = 24.285 Lb/hr
60 Second static flow test @ 0.770sg @ 4Bar = 297mL divided by 10.5 = 28.285 Lb/hr

Found here:
http://www.thirdgen.org/techboard/tpi/3 ... tings.html

I can get these 8 injectors for a case of beer - plus he really wants to see our Jeep run because he's been watching us work on it for months. I'm paying close attention to the differences in octane rating how it affects the specific gravity of the fluid passing through the injector. Mid grade around here is 89 which I'm thinking this Jeep will want to run at with a density of 0.740-0.745 depending on the E-content (around here it's 7-10% I keep reading). If I do my math correctly taking the liberty of manipulating the data above, 89 octane gasoline through the above injectors should sit right around 25.09Lb/hr at 3Bar, so at 49psi they'll be around 26.6Lb/hr +/- a few %. Dino if you were saying 25.7Lb/hr injectors were the recommended choice, these would give us room like you said for a better intake and exhaust which are in this Jeep's future. There are a few broken bosses on the '97 intake manifold we were hoping to replace down the line with the better flowing intake manifold, off-road snorkel/smooth intake & filter and an aftermarket exhaust downpipe.

Unless you guys have any strong objections I'm going to give these injectors a try. I'd rather run an injector a little too big and tune the PCM after the intake and exhaust have been replaced.

[Cheromaniac]

I have a local friend with an extra set of 02 LS1 injectors.

I can get these 8 injectors for a case of beer

Dino if you were saying 25.7Lb/hr injectors were the recommended choice, these would give us room like you said for a better intake and exhaust which are in this Jeep's future. There are a few broken bosses on the '97 intake manifold we were hoping to replace down the line with the better flowing intake manifold, off-road snorkel/smooth intake & filter and an aftermarket exhaust downpipe.

Unless you guys have any strong objections I'm going to give these injectors a try. I'd rather run an injector a little too big and tune the PCM after the intake and exhaust have been replaced.

Sounds like a good plan.

[Rinkrat456]

I should have known....what does JEEP stand for? Just Empty Every Pocket...right?

I swapped injectors to the new LS1/LS6 26.6lb injectors (note: at 49psi Jeep rail with 93 octane). I disconnected the battery lead during this time in hopes of resetting the PCM. After swapping injectors I babied it to the exhaust shop where I had a 2.5" exhaust bent up from the header to the tip with 2.5" universal Magnaflow cat and 2.5" in/out 5x7x14" Magnaflow muffler. Sounds really good now. On my way home I figured I'd start giving the engine a little more throttle now that fueling should be closer and exhaust is quieter (was running a small bullet muffler clamped on as a temp fix).

Anyways, I'm disappointed in the outcome. The stroker won't rev past 3000 RPM's in any gear, including park and neutral. It seems as though the rev limiter kicks in because it pops and bucks off the 3000 RPM mark. When driving and forcing it into 2nd gear, the same thing happens. It seems like I'm hitting a rev limiter at 3k. Also, when merging onto a highway keeping it in 3rd gear I floored it and from 1000-2000 it pulls nice and hard but it seems as though above 2000 it flatlines and I lose all my power. It just makes noise and hangs there while making it dangerous to get up to speed. It's hard to get up to 70mph from 40. There's just no power in the mid range at higher TPS amounts. When under high engine load/high TPS amounts I can hear a noticeable rattling/pinging noise that I can't tell if it's detonation or if it's valvetrain rattle. Either way I don't like it.

Also, now with the new LS1/LS6 injectors there's an immediate off-idle hesitation or a hangup when leaving a stop sign. Imagine letting off the brake from a stop, applying gas to accelerate normally and after the engine starts to accelerate it hesitates for a brief hiccup before continuing. It did not do this with the factory injectors, nor did it do this with way too large 39lbers I tried just for shits and giggles before installing the LS1/LS6 injectors that are in there now.

I have a few theories.

1. 180k miles on the stock fuel pump, perhaps it's on it's last leg. I have a buddy coming over this evening with his 8ft long fuel gauge/hose and I am going to take a pressure reading at the rail and under load. What should under load pressure be? If it turns out to be the pump, what options are there for the best bang per buck replacement choices?
2. When we swapped in the new engine, we replaced just the plugs and plug wires. The previous owner replaced the cap and rotor just weeks before we bought the Jeep from them, and they look new. However, the coil is stock as far as I can tell or it's a replacement that's really old. What symptoms would an aging coil present? Is it possible that the 9.55:1 compression and high cylinder pressures are killing the coil?
3. Is there a limp-home mode built into these PCM's that we're possibly fighting? GM's have it, do the Jeeps?

Help finish this once and for all!

Note though, we've gone through 2 tanks of gas now and are nearing the 500 mile mark now that I've been driving the Jeep to work, babying it on the highway. 16.01mpg the first fillup, 17.88mpg the second fillup. Similar driving styles 90% with highway cruising. it seems to be breaking in nicely. I just wish I could finally apply a full load to the engine and have it rev like it should be.

[SilverXJ]

Also, now with the new LS1/LS6 injectors there's an immediate off-idle hesitation or a hangup when leaving a stop sign. Imagine letting off the brake from a stop, applying gas to accelerate normally and after the engine starts to accelerate it hesitates for a brief hiccup before continuing. It did not do this with the factory injectors, nor did it do this with way too large 39lbers I tried just for shits and giggles before installing the LS1/LS6 injectors that are in there now.

Perhaps the PCM needs to learn around that.

1. 180k miles on the stock fuel pump, perhaps it's on it's last leg. I have a buddy coming over this evening with his 8ft long fuel gauge/hose and I am going to take a pressure reading at the rail and under load. What should under load pressure be? If it turns out to be the pump, what options are there for the best bang per buck replacement choices?

You have a 98 right? 49psi +/- 5 psi.

2. When we swapped in the new engine, we replaced just the plugs and plug wires. The previous owner replaced the cap and rotor just weeks before we bought the Jeep from them, and they look new. However, the coil is stock as far as I can tell or it's a replacement that's really old. What symptoms would an aging coil present? Is it possible that the 9.55:1 compression and high cylinder pressures are killing the coil?

Could be a possibility. Check the color of the spark for a start.

3. Is there a limp-home mode built into these PCM's that we're possibly fighting? GM's have it, do the Jeeps?

Nope.

What if your AFR when this happens?

Where did you get the injectors from?

[Rinkrat456]

Also, now with the new LS1/LS6 injectors there's an immediate off-idle hesitation or a hangup when leaving a stop sign. Imagine letting off the brake from a stop, applying gas to accelerate normally and after the engine starts to accelerate it hesitates for a brief hiccup before continuing. It did not do this with the factory injectors, nor did it do this with way too large 39lbers I tried just for shits and giggles before installing the LS1/LS6 injectors that are in there now.

Perhaps the PCM needs to learn around that.

1. 180k miles on the stock fuel pump, perhaps it's on it's last leg. I have a buddy coming over this evening with his 8ft long fuel gauge/hose and I am going to take a pressure reading at the rail and under load. What should under load pressure be? If it turns out to be the pump, what options are there for the best bang per buck replacement choices?

You have a 98 right? 49psi +/- 5 psi.

2. When we swapped in the new engine, we replaced just the plugs and plug wires. The previous owner replaced the cap and rotor just weeks before we bought the Jeep from them, and they look new. However, the coil is stock as far as I can tell or it's a replacement that's really old. What symptoms would an aging coil present? Is it possible that the 9.55:1 compression and high cylinder pressures are killing the coil?

Could be a possibility. Check the color of the spark for a start.

3. Is there a limp-home mode built into these PCM's that we're possibly fighting? GM's have it, do the Jeeps?

Nope.

What if your AFR when this happens?

Where did you get the injectors from?

No idea on AFR, I need a scan tool or a wideband but currently have neither. I would prefer a scan tool over WB for this particular project.

Injectors I got from a guy on LS1tech from a running vehicle with 65k miles on them.

[Cheromaniac]

I have a few theories.

1. 180k miles on the stock fuel pump, perhaps it's on it's last leg. I have a buddy coming over this evening with his 8ft long fuel gauge/hose and I am going to take a pressure reading at the rail and under load. What should under load pressure be? If it turns out to be the pump, what options are there for the best bang per buck replacement choices?
2. When we swapped in the new engine, we replaced just the plugs and plug wires. The previous owner replaced the cap and rotor just weeks before we bought the Jeep from them, and they look new. However, the coil is stock as far as I can tell or it's a replacement that's really old. What symptoms would an aging coil present? Is it possible that the 9.55:1 compression and high cylinder pressures are killing the coil?
3. Is there a limp-home mode built into these PCM's that we're possibly fighting? GM's have it, do the Jeeps?

Help finish this once and for all!

1. I think the Chevy LS1/LS6 injectors may be part of the problem. You're operating them at 49psi when they were designed for a 58psi (4 bar) fuel pressure so the fuel may be dropping out of suspension due to insufficient atomization.

2. A failing fuel pump could indeed be the reason why your engine won't go past 3000rpm. The stock pump should flow 90lph (24gph) or 1.5 liters/min.

3. I seriously doubt that the compression is killing the coil. A bad coil usually causes difficult starting or a no start situation.

4. The Jeep PCM doesn't have a limp home mode.

[SilverXJ]

No idea on AFR, I need a scan tool or a wideband but currently have neither. I would prefer a scan tool over WB for this particular project.

A scan tool will be useless to tell you what the true AFR is. The scan tool will tell you only 3 things. Lean, Stoich, and Rich. Not actual values.

I'd put money on the fuel pump.

[Rinkrat456]

No idea on AFR, I need a scan tool or a wideband but currently have neither. I would prefer a scan tool over WB for this particular project.

A scan tool will be useless to tell you what the true AFR is. The scan tool will tell you only 3 things. Lean, Stoich, and Rich. Not actual values.

I'd put money on the fuel pump.

I've used scan tools/hand-helds that tell you the fuel trims. Negative values mean it's rich, positive values mean it's lean...closer to 0 the better. That would be fine for me and for this project.

[Rinkrat456]

1. I think the Chevy LS1/LS6 injectors may be part of the problem. You're operating them at 49psi when they were designed for a 58psi (4 bar) fuel pressure so the fuel may be dropping out of suspension due to insufficient atomization.

2. A failing fuel pump could indeed be the reason why your engine won't go past 3000rpm. The stock pump should flow 90lph (24gph) or 1.5 liters/min.

3. I seriously doubt that the compression is killing the coil. A bad coil usually causes difficult starting or a no start situation.

4. The Jeep PCM doesn't have a limp home mode.

1. I thought above we agreed these injectors would be a good choice?
2. Would a failing fuel pump cut the engine in both neutral, park and drive so abruptly? Is there a sensor that also cuts the engine RPM's so drastically? I'll get a video if need be.

[SilverXJ]

I've used scan tools/hand-helds that tell you the fuel trims. Negative values mean it's rich, positive values mean it's lean...closer to 0 the better. That would be fine for me and for this project.

I know how scan tools work. They won't tell you anything about open loop/WOT AFRs.

[CobraMarty]

An OBD2 tool like Torque Pro or Scangauge will tell you open/closed loop in real time.

[SilverXJ]

An OBD2 tool like Torque Pro or Scangauge will tell you open/closed loop in real time.

It tells you when it goes in to open/closed loop. Still doesn't tell you anything about the AFR in open loop.