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02:23:52 - 05/02/2024
Dakota Performance
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Noohki
GenII
 
3/21/2006
00:13:57
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 Subject: 5.9 Gen II Running Lean
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Message:
Last year I purchased a 94 RC, 5.2 dakota on ebay which had 206,000 miles at that time knowing that I would probably have to replace a lot of parts. After two months of driving it, I replaced the 5.2 with a 2001 5.9 from a bone yard and added a Hughes her1418al cam with their springs along with used Gibson headers, 3 in. exhaust system, and a Mopar Performance computer for a 94 5.9 Ram. . I also added a K&N cold air intake system and relocated the IAT sensor and installed a new oxygen sensor. At that time I kept the 206,000 mile fuel injectors.
It ran really good until last summer at which time I started to notice a power loss at full throttle. Other than that, the motor still ran fine and had excellent gas mileage (as long as I kept my foot out of it). I then purchased a 52mm hughes throttle body, installed new FMS 21 lb injectors, set the TPS voltage to .7 v, and installed bosch platinum +4 plugs in attempt to correct my full throttle problem. It did not help but did not hurt either.
I drove my Dakota with this problem with no other problems but lately I noticed it pulled a lot harder at part throttle vs. full throttle. I thought it might be the fuel pump so took it in to a local mechanic.
I told the mechanic I thought it was running lean so he checked it on his diagnostic machine and told me the air/fuel ratio and fuel pressure was well within parameters but he did notice the bosch platinum +4 plugs were reading rich and recommended putting in the stock plugs. Instead I had him put in the autolite 3923 plugs.
He then told me the engine was running lean with the autolites and since everything else checked out OK he OK recommended a new fuel pump.
After he installed the new fuel pump he said it was still running a little lean at 14.8/1 at idle. He then checked the impedance of the FMS injectors and said that they were running too low on impedance (9 Ω) for a 94 dakota. This is where I’m at right now.
Do any of you have any experience or any ideas what the problem might be? This is getting expensive.
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The Purple1
DakotaEnthusiast
3/21/2006
03:22:33
|  RE: 5.9 Gen II Running Lean
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Message:
Hi Noohki!
In your area; try a second opinion from another mechanic or shop... rather than letting this one chase his tail some more and cost you more money!
Actually, 14.8:1 air/fuel ratio is almost exactly what the computer aims for under anything but cold warmup or wide open throttle conditions. "Stoichiometric" (big, fancy word for "best mix for power, fuel economy, and emissions") air/fuel ratio for gasoline-fueled engines is 14.7:1.
When the mechanic used his "diagnostic machine" and checked fuel pressure, he prob did it only at idle, right? I would definitely check it under the conditions you're having trouble with. Get a fuel pressure gauge and, carefully running the hose out from under the hood, tape it to the windshield where you can see it while driving. Then test drive the truck (sounds like a cool ride, by the way) and see what the fuel pressure does under the right conditions.
Fuel injectors that are too low in impedance can cause computer troubles as well. The most likely one that comes to mind would be overloading and damage of the computer's injector "drivers", that is, the circuits that send power to the fuel injectors. I don't remember the impedance specs called for for our trucks, but 9 ohms sounds about right... I don't think this is causing your problem, anyway.
Keep us posted!
360 Air Intakez, 52 MM Holley Billet, Ported, Hughes Plenum Plate, Perma Cool Fan, Jacobs Pro Street, Moroso Ultra 40, Bosch 4, Superchips, TPS, CPS, IAT Mods, Dynomax Ultra Flo, Transgo, SLT Trim, Diamond Heads & Corners, Clear Tails, Hood Pins, APC White Gauge, PML Polished Trans & Diff Covers
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2003flrt
R/T
3/21/2006
17:40:00
|  RE: 5.9 Gen II Running Lean
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Message:
i agree with purple1. 15:1 is where A/F mix should be. maybe the computer is on the way out. when they go they can make car act funny. i had a pontiac that had a computer problem. i checked everything and changed fuel pump because it would stall out at anytime w/o warning. i had goodyear check the computer and it was going bad. i had well over 170k on car at the time.
2003 R/T Superchips,cai,tps mod,map mod,iat relocate,Sirius sattelite radio,autolite 3923's
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Noohki
GenII
3/21/2006
22:24:40
| RE: 5.9 Gen II Running Lean
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Message:
Thanks for your responses.
The mechanic asked if I had the old (206,000 mile injectors),I did, but before I took them in to him I checked the resistance and they were 14.8 ohms. This is opposed to the FMS injectors which were at 9 ohms.
The mechanic also clarified a few things for me. The 14.8/1 afr was as rich as it ever got. He said it hovered in mid to high 15s. The 14.8 was only at idle.
I also brought in the oem computer. He checked the air/fuel ratio with the oem computer while I was there and there was no change.
We took a test ride to see how it ran. It had a moderate case of pinging, even with 92 octane.
Before I left today he tested the injectors. I didn't understand all of the technical terms but he said something about the hold time being too long according to the specs. He said in other words the injectors are saturated even at idle.
Tommorrow he's going to try the oem injectors.
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Noohki
GenII
3/24/2006
23:33:51
| RE: 5.9 Gen II Running Lean
IP: Logged
Message:
Problem solved! The culprit was a broken wire going into the wiring harness to the pcm.
It is not running lean anymore and is running like its supposed to.
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