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Dodgerench
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3385
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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I have a 95'3/4 tn. It starts ok. Idles ok. Then start to

Customer Question

I have a 95'3/4 tn. It starts ok. Idles ok. Then start to drive,check engine light comes on.Truck runs really rough,backfires when let off gas.Stop,turn off.Let set a few minutes ,then start,and runs fine for a bit ,then starts again.Thank you
Submitted: 1 year ago.
Category: Dodge
Expert:  Dodgerench replied 1 year ago.

Goood afternoon, welcome to JustAnswer!. This is Ed.

Rather than speculate just yet, I think the best thing would be to find out what codes are being stored in your PCM (engine controller) memory. When you have a CE light illumination while driving, you will have something stored and it's likely to be significant.

If you have a scan tool or can have someone scan the truck... great! This is by far the best way to find out what the specific code being stored actually is, but another (less accurate) way of pulling codes needs no scan tool. It's called the "flash method" and can be done in your driveway. We're going to do a quick key dance, then count flashes of the CE light without the engine running. It goes like this.

Hop in the truck and shut the door. Roll the key from off to on three times within five seconds, leaving the key ON after the last cycle. For those counting at home it goes OFF-ON-OFF-ON-OFF-ON (leave ON).

Watch the CHECK ENGINE lamp as it does a longer than normal "bulb test", eventually going dark. Get ready to start counting flashes.

Flashes will come in bunches, with short and long pauses in-between. Short pauses tell you to keep counting, longer pauses mean the previous digit is done (write it down). All codes are binary, having two digits (like 12, 22, etc), so when you're done, there should be an an even number of digits on your sheet. Code 5-5 will always be the last to be flashed, meaning this is the end of the test.

Feel free to repeat the test a few times to get the hang of it, or just get the truck scanned. The trouble with the flash method is that some codes (like 21 for oxygen sensor) can have several variants that are completely different in meaning, but since they include the oxygen sensor to some degree, they get lumped together because only so many flash codes can exist.

I'll stop there for now. Let me know what you find and the actual model year of your truck (or VIN, I can decode), because the 95 to 96 model year was a transition between OBD-1 to OBD-2, which is significant. A truck built in September of 95 is most likely a 96, but it does make quite a great deal of difference. If there is a great deal of backstory or you'd just rather do less typing, I'm available over the phone for a personal 1-on-1 to help sort things out.

Talk in a bit,

Ed

Customer: replied 1 year ago.
I got a code of 34. Witch I googled .Said speed control sensor?
Customer: replied 1 year ago.
3b7kf23w8smi83845
Expert:  Dodgerench replied 1 year ago.

I think that's an EGR solenoid circuit code. Lemme check...

Expert:  Dodgerench replied 1 year ago.

You were closer; it's for speed control. This code will set if you have a problem with the cruise control servo or if your truck isn't equipped with cruise control in this (the 1995) model year. Either way, I don't see this code as a good indication of what's gone wrong, running-wise.

I show your truck to have a V10, so your truck would be using OBD-1 diagnostics even if it was a 96. The HD version of the truck line with the 8-liter got a special pass on OBD-2 certification, but by the same token, its self-diagnostics aren't as keen as the OBD-2 trucks, either.

Expert:  Dodgerench replied 1 year ago.

What happens if you go to wide-open throttle when the engine is struggling? Does it improve? Get worse? Stay the same?

Customer: replied 1 year ago.
Stays the same. Big miss.Top speed of 60 and that's pedaling it
Expert:  Dodgerench replied 1 year ago.

I see. So it's not really a general loss of power, it's showing roughness or misfire? And it stays that way until you actually turn it of and let it sit for a few minutes.

What happens if you do an immediate restart? Still rough?

Customer: replied 1 year ago.
No. It goes away for about 100'. Then starts again.
Expert:  Dodgerench replied 1 year ago.

That's a pretty quick turnaround, tho.

By the sound of it, we're probably losing spark or injector flow to just a few cylinders... not the whole engine. I'll send you a little info on this version V10 that might explain some things, then let me know what you think. It'll take a little while to type this out, so grab a cold one.

Customer: replied 1 year ago.
Thanks
Expert:  Dodgerench replied 1 year ago.

The V10 was unique in its engine controls before 96, because the existing engine controller of the time was the old SBEC-2 unit, which just didn't have enough circuits to operate ten cylinders. The solution was to couple the SBEC-2 with an auxiliary module for coil control, but because this was pre-OBD2, there really weren't any good self-diagnostics included. If the auxiliary coil controls took a dump, you'd lose spark to up to 4 cylinders but nobody knew what was going on.

Expert:  Dodgerench replied 1 year ago.

Another thing I've seen rarely -- but always on the V10 from this time period -- is a contamination problem that affects the fuel injectors. An oxidation or some thing collects inside the stainless steel can at the top of the fuel pump module, outside of the filter medium. Fuel is pushed up by the pump... passes through the regulator... reaches the pleated paper filter inside this can... then gets crapped up with particulates on it way to the engine. With no return path to flush the system out, anything that goes forward gets collected in the screens of the injectors, eventually causing a restriction problem.

Expert:  Dodgerench replied 1 year ago.

It's not an even contamination, either. The ones affected most are at the rear of the engine, where fuel is first dumped into the injector rail. So the back injectors get packed with debris, while the front ones operate somewhat cleaner.

If you have contamination problems, I'm imagining that the fuel actually boils a bit with the hot engine when you shut the engine off, momentarily aerating and loosening the debris packed into the inlet screens. Then it gets packed down again once flow is resumed and things get bad again.

Customer: replied 1 year ago.
Will hurt to drive it. I'm 100 miles from home. Sounds like fuel or replace the 2 ea coil controls?
Expert:  Dodgerench replied 1 year ago.

The injectors will click audibly just as they normally would, but might be slightly louder since they're not immersed in fuel at the valving. I'm speculating at this point because I don't know for sure.

Expert:  Dodgerench replied 1 year ago.

Dang, I'm not sure. I'd check for available spark first to see if it's the problem.

Customer: replied 1 year ago.
Thank you.
Expert:  Dodgerench replied 1 year ago.

I'd pull each of the 5 spark plug cables loose at the plugs, but leave them resting on the plugs. Then start the engine and wait until it's misfiring. Lift each plug wire carefully to observe spark strength from the plug wire to the plug. You should be able to generate 3/4 to a full inch of spark

Expert:  Dodgerench replied 1 year ago.

If you find a serious lack of spark in one or two (probably two) plug wires, it's quite likely a problem with the aux. controller, which will be very very hard to find. I'm not sure that they're even built any more.

Expert:  Dodgerench replied 1 year ago.

Another quick question since you're on the road. Did you just refuel right before this started? It might be water that's messing with you.

Expert:  Dodgerench replied 1 year ago.

Given the slope of the engine, small amounts of water contamination would pick on the rear cylinders, where the front ones would be treated to better fuel.

Customer: replied 1 year ago.
I fueled at a Chevron.
Expert:  Dodgerench replied 1 year ago.

Would you like to talk this over on the phone? JA does charge for the service, but I can discount it from here.

Ooooo... JUST filled up? Within 5 miles of when it started acting up?

Expert:  Dodgerench replied 1 year ago.

Did you call the Chevron to see if they've had problems?

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