94 Dodge ram 4x4, runs super rough.

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Cope

Cope

Fusing with fire
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Our shop truck is giving me fits. In fact it has stumped 3 shops so far.

Here's the story.

Bought the truck for 400.00 dollars. Threw everything away except the cab and frame. Rebuilt the truck from the groumd up.

Got a good running 360 mag from a buddy and put it in. All was well.

Pops blew the trans cooler line and smoked the trans.

Had trans rebuilt by a local trany shop.

Shop calls and says trans is in but the truck wont run. ?????

I go down and look over the truck. Everything seems ok. Spark, cylinder pressure, fuel are all good.

Truck will fire and run normal but as soon as its up to temp it shutters VERY BAD. Undriveable bad.

Now not trans shutter, RPM flutter.

Trans shop sends it to their mechanic and two weeks go by. They cant fix it. Some deal was reached between pops and trans guy for money off the bill or some such. I forgot it was a while ago now.

Take the truck to my buddys shop. 4 days. He changed out a bunch of sensors and could not fix it. So we payed for the parts and towed the truck home.

Now i got sone time im wondering what the hell is wro g with this thing.

Talking to a buddy and he mentioned they had one where something in the gauge cluster was unsoldered, soldered it up and ran fine. (He cant remember what it was but said it was a dodge mini van.)
He also mentioned that the ECU in these trucks oftend crap out.

The strange thing is, it runs and drives great until it gets warm and BOOM, now your are looking to pull over right tue F now beacuse it seems like it will die at any second. (Some times it dies, some times it recovers)

Any ideas what the heck is wrong?

Pops would be very happy to be driving his fancy truck again. Thank you!
 
Sounds like the ECU is fragged. Try clearing it (disconnect all power for one minute and ground the ECU frame). Then try a restart and let it idle for a good 15-20 minutes before driving.

If the issue returns, you probably need a new ECU. They often go bonkers once they get hot if they are failing.

The only other possibility I can think of is that the throttle position sensor is fragging at temp and giving false readings to the ECU.
 
I would look for some temp sensors and disconnect those
see if that changes

(I'm guessing something is putting it in a form of limp mode)
 
Throwing any codes? Still have a catalytic convertor on it? Had a 97 Ram 360 magnum. Leaving work one day it ran great until 2 miles down the road and almost to operating temp. Limped it 8 miles home with the 4 ways on. Cooled down few hours later and ran fine until it got warm again. Ended up being the catalytic convertor had failed.
 
diymirage said:
I would look for some temp sensors and disconnect those
see if that changes

(I'm guessing something is putting it in a form of limp mode)
Click to expand...
Limp mode doesn’t do what he described, it just limits RPM but doesn’t make it run rough.
 
ragtopfury said:
Throwing any codes? Still have a catalytic convertor on it? Had a 97 Ram 360 magnum. Leaving work one day it ran great until 2 miles down the road and almost to operating temp. Limped it 8 miles home with the 4 ways on. Cooled down few hours later and ran fine until it got warm again. Ended up being the catalytic convertor had failed.
Click to expand...
It might be the cats...or even the O2 sensors as they kick in after it gets warm and the ECU runs off of the sensors rather than the program tables.

I doubt it though, it sounds like the ECU is fragging by the description.
 
Ddaddy said:
Limp mode doesn’t do what he described, it just limits RPM but doesn’t make it run rough.
Click to expand...
correct, but if all we got to go on is temp, why not check with the things that register that?
 
I’ve had 3 of those 2nd gen Rams and I believe its the 02 sensors. My last 01’ Sport 5.9L did the same thing and I changed out everything, the 02 sensors were last and it ran better than it ever did once I changed them.
 
I tend to agree with the o2s being the problem but

Firstly, most of those old systems, with un-heated O2s, have a pre-programmed cold-start map, and the engine runs on that until the ECU sees a certain coolant temp. This was called open-loop because the O2s were not in the loop.
Then, when the magic number comes up in the coolant sensor, the ECU switches to closed loop and the O2s run the show, with the ECU making second by second, short-term corrections. If the computer makes the same old corrections over and over, it throws some of the correction into a long-term correction.
Now, while this goes on day after day and the miles pile on, the computer is keeping track of all those corrections that it has been giving.

They call this a speed-density system, because the two major players in the fuel maps are ; engine speed, and oxygen density. So the rpm sensor is the first go-to, and the load sensor is the second; the load-sensor sensing manifold vacuum. The ECU reads those first, then checks it's pre-programmed map to determine how long to open the injectors. Then it checks the long-term trim, and adds that in. Then the short term trim, and adds that in. While you were cranking the engine, it checked the baro-sensor, and that correction is continuously added. Of course it is also continuously monitoring the temperature of the coolant and the inlet air, and making corrections for those. Finally with all the corrections added up, it opens the injectors and immediately checks the O2s to see if it did a good job.
If the Ecu figures it made a mistake, then on the next go-round, it makes another correction.
You can see this on the scanner as the O2 is continuously switching from rich to lean in response to the oxygen content.
Ok but hang on; what if oxygen was getting into the pipes ahead of the O2s and corrupting the reading? Heckya! If you have an exhaust leak, chances are,not only is exhaust leaking out, but atmospheric air is also leaking in; which is 21% oxygen.. Check it out. I bet the trans shop dropped the exhaust ..................

So if you disconnect the battery for a period of time, the computer loses the records of these trims. So it has to start all over. So it takes TIME, in the form of driving cycles,, for the computer to re-establish the trims. Eventually, it will sort it out. Well as long as the O2s and CTS are working, it will.

If you put a scanner on it, you can read in real-time, what the O2s are doing. My cheapo tool even graphs them. The scanner can also read all or most all your major sensors.
 
I know for a fact the O2 sensor is new. I remember my buddy thinking that was the issue.

Itdid have a major exhaust leak when i first picked up the truck but i made the trans shop fix that.

94 is OBD1(?) so my scanner wont work on the truck.

I don't remember if the truck has a cat.

Thank you!

These all sould like great ideas. I will try all the above and report back.
 
Also remember on that sensor auto shop A1A because you bought it brand-new doesn't mean it works...
 
Is the intake gasket blown like a lot of the Magnum motors do? The intake leaks and clogs the O2 sensor and then they run really bad when they get up to temp. You need to look at what the computer does when it gets to temp....retards spark....backs down fuel...so if it runs fine when it's cold with more timing and more fuel then where is the fuel pressure or timing when its warm?
 
Different problem but one to watch for is that valley pan on the intake. If you start using like a quart of oil every hundred miles and it pings and gets bad gas mileage it's something to look at...
Fixed that on my 98 and couldn't be happier haven't used any oil since...
 
j par said:
Different problem but one to watch for is that valley pan on the intake. If you start using like a quart of oil every hundred miles and it pings and gets bad gas mileage it's something to look at...
Fixed that on my 98 and couldn't be happier haven't used any oil since...
Click to expand...
Not really a different problem...this goes undetected for a lot of these motors for a long time...what happens is it gets fixed eventually but, the whole time it was leaking it has completely screwed up the O2 sensors...
 
A few things i recall from my time at the dealership back then.
If it is a returnless fuel system, the regulators on top of the pump go bad. They arent hard to change.
The ignition coils on those trucks go bad, you carry a spare like you do with a ballast resistor in the older cars.
Cam/crank sync could be out, if distributor was removed and proper timing procedure wasnt followed. Need a scan tool.

trans was out,crank sensor may be damaged, first thing i would look at. Not the first time i have seen that, dropping trans without pulling crank sensor first will most often crack it.

only thing i have left and can suggest is coolant temp sensor.

taking it to multiple shops because the last one couldnt fix it is not the best thing to do, you are paying someone to retrace the last guy’s steps.
 
plymouth67 said:
Not really a different problem...this goes undetected for a lot of these motors for a long time...what happens is it gets fixed eventually but, the whole time it was leaking it has completely screwed up the O2 sensors...
Click to expand...
I know the problem was going on with the previous owner and I let it go for at least a year or so and as soon as I corrected it I actually didn't change any sensors and everything seems fine but again what may work for one person may not for another..
 
Had an oil pressure switch act like that one time.
It was faulty and sending false information to the computer, thinking the engine had no oil pressure.
It would shut the engine down, that took me a while to find.
 
Tooljunkie said:
A few things i recall from my time at the dealership back then.
If it is a returnless fuel system, the regulators on top of the pump go bad. They arent hard to change.
The ignition coils on those trucks go bad, you carry a spare like you do with a ballast resistor in the older cars.
Cam/crank sync could be out, if distributor was removed and proper timing procedure wasnt followed. Need a scan tool.

trans was out,crank sensor may be damaged, first thing i would look at. Not the first time i have seen that, dropping trans without pulling crank sensor first will most often crack it.

only thing i have left and can suggest is coolant temp sensor.

taking it to multiple shops because the last one couldnt fix it is not the best thing to do, you are paying someone to retrace the last guy’s steps.
Click to expand...

Crank sensor was replaced after the trans shop.

I agree, i have no odea why dad agreed to even take the truck. The trans shop should have fixed it. I think pops thought it would be an easy fix ( for me, not him) im guessing he figured id fix it, he saves money and its a win win for him... well 6 months later id bet he is rethinking that...
:)
 
sireland67 said:
Had an oil pressure switch act like that one time.
It was faulty and sending false information to the computer, thinking the engine had no oil pressure.
It would shut the engine down, that took me a while to find.
Click to expand...

thats what im thinking...a sensor going haywire and starting a domino effect
i wonder if you can bench test all those sensors?
 
diymirage said:
thats what im thinking...a sensor going haywire and starting a domino effect
i wonder if you can bench test all those sensors?
Click to expand...
Some can, scan tool is necessary for some though. Easyautodiagnistics has some good sensor test procedures.
 
The cheapest thing "just to throw at it" will be a temperature sensor. They can reek havoc when they go bad.
 
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Cope, your first step should be to set fuel sync. It can cause exactly what you are describing. Usually it is done at the dealer with a scan tool. But there is a procedure for doing it at home.
 
^^
Entirely possible as the distributor may have been removed and replaced by the trans shop in an effort to 'make the vehicle run' after a ? 2-3k $ rebuild.
cope said:
It did have a major exhaust leak when i first picked up the truck but i made the trans shop fix that.
Click to expand...

cope,
no scan tool needed on Dodge truck OBD1 ...
key ON, OFF, ON, OFF, ON -- observe and record the dash 'flashes' from the amber
siloutte of the ck engine lamp .

With Very Humble Respects Honored Posters --
cope May I suggest a code baseline -
?Dash code cold?
?Dash code hot ?
 
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