My '89 Dakota has a freshly swapped Magnum 5.2 (EFI) which I've only recently been able to test on the street. It's a '92 motor (from a Dakota), '92 ECU (from a van), a CAI and, a fairly free flowing exhaust system. With maybe 10 to 15 miles of road time it isn't yet running as well as I'd like. I imagine the reason is because it may take more time for the ECU and the components to get acquainted, but does anyone have an idea about how long? It idles well, but when you accelerate it seems kinda flat, like you might expect if the timing were off. Also, when you back off, there's a lot of rumbling and popping through the exhaust. It's a single 3" exhaust, thru a Y-pipe, a new hi-flow Magnaflow convertor and Magnaflow XL muffler. Many new components on the motor: fuel regulator, CPS, fuel filters, etc. The motor itself had about 90K miles on it when it was torn down and gone over by an SAE certified mechanic. It was the subject of a mechanic class at a vo-tech school one semester, and everything that was worn was replaced. I will say it seems ever so slightly better each time I've driven it, but I'm eager to get it right. Just need more time/miles, or is there something I might be over-looking?

 

I can't find a definite statement in the FSM, but I vaguely remember it being about a tank full - around 300 to 400 miles.

It also sounds like it's running a bit rich; did you also change out the fuel pump in the tank since the TBI design wants about 14.5psi; the EFI wants 35-45 PSI instead. Your pump may just not have enough fuel flow if it's still factory (and also, the fuel pressure regulator was on the TBI body; the 1992 is expecting it to be in the tank, so it may be worth triple checking fuel pressure to make sure it's inside spec.)

RwP

 

Thanks for the input on the ECU adjustment period. I think you're right about it running rich, it fits the way its behaving. Maybe that's a default condition while the ECU adjusts? The tank and pump are from a Magnum 5.2 so it has the higher pressure, and since its a '92 it has the regulator on the fuel rail with a return line to the tank. The regulator is new, and the lines were flushed during the rebuild.

I am using an older O2 sensor, so I'm starting to wonder if its failing, keeping the ECU in an open loop condition. Might that cause it to run rich? I don't know how many miles were on the sensor, probably a lot.

 

Well, the sensor won't affect it open loop - but it may be causing it to run tres rich on closed loop. And if it's old, you won't get optimum performance.

Also, next thing is to double-check the fuel pressure (wouldn't be the first time a new pressure regulator failed!), also make sure that's a 5.2 ECU not a 5.9 ECU (which run pig rich for the 5.9, and will just about flood out a 5.2!)

Ideally you'd find a 1992 Dakota ECU for it, IMO.

RwP

 

Yeah, I can't say that it's rich right from startup. I usually let it warm up before I drive it. So if the O2 is not signaling, I was thinking it might never actually go into closed loop because the ECU would never get feedback and therefore keep the mixture rich. The burbling and popping in the exhaust also suggest a rich condition to me, like unburned fuel passing thru. I'm going to go ahead and replace the O2 sensor, just because it's old and might cause problems. I will put fuel pressure check on the list as well.

You bring up a good point about the possibility of it being a 5.9 ECU, but I don't think it is. The reason I say that is because it came out of a '92 van, and if I remember correctly, the 5.9 didn't get the Magnum treatment until '93 (saw that somewhere a while back). Anyway, I have another ECU I can try; its a Mopar performance ECU for a '92 5.2L. Requires premium fuel, but at least gas prices are lower now!

 

Ragged, most of my experience is with GM. That said, I have a 93 corvette, obd1 I have a older Autoxray and it will scan as well as monitor each sensor or input. That being said, I can look at closed loop, or open, also I can look at the 2 O2 sensors and see them change readings. Not a sure test as they can become lazy, but at least you can see they are working.
But in the end, I think you need a wide band o2 with a guage to determine it is rich or lean.
Or, if possible, can you take it to a dyno shop, and it be tuned? I have no idea what the tuning capacities are on the chry. computers.
I can tell you on a GM I have spent way more then I care to talk about and Im still not 100% satisfied with the tune.
I know I am rambling, but this is another reason I plan to go carb. I understand it better!!

 

OK. I've run across this - www.boostbutton.com - and they have a SCI/FTDI board; you can buy a FTDI/USB cable (total outlay is on the range of $60 for the pair with shipping); the MPScan and MPTune software is free; to tune you do need to either socket the SBEC/SBEC-II you have or at least convert it to flashable (which also requires a socket), and if you don't convert it to flashable, you do need to buy a EPROM programmer for it.

All of THAT said ... I'd grab that setup and an old laptop, and go to town on monitoring it.

MPScan is supposed to be able to monitor the ECU and query what it's seeing (as in "Why are you going to -14 on the STFT?"), and MPTune will allow you to dump the changed tune into a flashable EEPROM, or dump out a .ASM file to burn into a EPROM/EEPROM on a burner.

Now, that last paragraph is from studying the forums on the turbo 2.2/2.5 Mopar motors, the Wiki at BoostButton, and a few other posts - I have no actual experience right now on that. But ... it'd be worth checking out, I do believe.

RwP

 

Also, if you tackle tuning yourself - I'd HIGHLY recommend Greg Banish's book(s) ( I have http://smile.amazon.com/Engine-Manag.../dp/1932494421 myself) for a better grasp of what they're doing.

Down side, Banish is mostly MAF, not MAP; up side, he DOES cover MAP also.

He also offers suggestions for tuning a ECU in it.

RwP

 

Great info guys, thanks. Honestly, I didn't know about these options for altering the programming on Mopar OBD1. I keep reading this stuff and I'm going to be tearing into this thing to see what I can mess with. I have a Bosch wide band O2 sensor I purchased a few years ago when I was playing with a MegaSquirt2 in my Neon RT. No gauge though, so I'd have to find one. I don't know, would that wide band sensor (for a Neon) work?

I've got to keep this simple for now so first I'm going to plug in a replacement O2 sensor and see what happens. If nothing good happens I'll check fuel pressure.

My son, who originally bought the truck, is visiting with his family, so for now I'm going to hold off on any serious troubleshooting - for a few days.

 

Ragged, if you want to send me a pm or e-mail. I would like to talk to you about my autoxray 500. I think it would really help you in diagnosing sensors etc.
For my next statement, I may get flamed, but I wouldn't think of trying to modify the programming tables on a mopar.
In short, there is tons more information out there concerning tuning a obd1 GM and for me its mind boggling.
There are so many things such as a coolant sensor not sending the proprer signal to the ecm that could cause it to run rich etc.
Look up autoxray 500 and if you are interested let me know.
In short, with a stock cam, injectors, CID and compression, you should not need a new tune.
Oh, and my comment on a wide band was ment with a guage to determine if you are running rich or lean.