autopar3000
Well-Known Member
My OBD1 setup runs at 52 psi and it runs fine. (I use a filter / regulator from a 2002 Jeep Cherokee, which has a 52 psi spec.) So yeah, I would agree - crank that pressure up and see what happens.
OBD I to OBD II Conversion Issues
- Thread starter tcanin00
- Start date
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tcanin00
Well-Known Member
Mine didn't like more the 42 psi or so on OBD I, weird.
I adjusted the pressure up to 52 psi and it runs much better. I could tell a difference in idle quality while I was adjusting it. There's still some misfiring, but it's not as bad as before. I'll leave the fuel pressure where it is and change the injectors when I get them.
tcanin00
Well-Known Member
Something else I have been thinking about, is it has long tube headers and 2.5" dual exhaust. The oem O2 sensor is in the right bank just after the collector. I'm thinking that since it's only getting half of the exhaust flow compared to being in a factory y-pipe, it's not getting an accurate reading. I was thinking about adding an x or h pipe. Should I move the O2 sensor where it's reading both banks of exhaust?
fueliedart
Well-Known Member
Is the system configured for dual sensors? I have seen systems used on V type engines that only read one bank. I would be surprised if that is the problem but experimenting is how a lot of problems get resolved. The 5.2 I put in my truck had a weird missfire at around 1800 RPM. The engine only had less than 2K miles on it when I put it in my 83 Ram. It drove me nuts. I tried everything to make it go away. I bought a factory service manual and tried troubleshooting the problem. A friend of mine was at a dealership and explained my dilemma to a mechanic he knew. The mechanic said there was a campaign on such a problem. He printed it up, my friend gave it to me and it ended up being something that was not in the FSM. The distributor was not installed correctly from the factory. There was a timing procedure that involved putting the engine on #1 TDC, turning on the key and rotating the distributor with a volt meter attached to the signal wire and watching for a high to zero area and locking the distributor on the high reading. It worked. Holy crap was I happy. What did the FSM say about timing? " Timing is adjusted by the computer and cannot be adjusted". That of course was way back when, when the Magnums were new on the scene. I'm thinking now that the truck got rolled because it had that very issue and the dealer couldn't fix the problem and the campaign hadn't been released yet, but I couldn't say for sure. Just a little something from my past about a simple mis-adjusted distributor that caused a problem that drove me nuts. BTW using the Jeep filter ( some people use a Corvette filter instead ) and going returnless is I feel the way to go.
autopar3000
Well-Known Member
You don't need an O2 sensor on each bank, I think only the HD Magnums were set up that way and I believe they're not smart enough to adjust one bank of injectors and not the other. Here's my OBD1 engine setup, for reference:
- Doug's long tube headers, with a single O2 in the right collector.
- I switch between the factory PCM and the Mopar Performance PCM, depending on whether I want to spend the money for premium fuel.
- 52 psi filter / regulator.
- Hughes SER0814ALN-14 cam and their spring kit.
- Mopar Performance M1 intake.
- 53 mm throttle body
The car runs great, so I don't think the headers or single O2 are your issue.
I don't remember, did you try disconnecting the O2 sensor? Mine went bad a little while ago and the car ran like garbage, but when I unplugged the O2 it was fine - just running in open loop, so way rich.
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autopar3000
Well-Known Member
Yeah, that's the fuel sync. It could definitely be part of @tcanin00's issue. The service manual has a procedure where you point the rotor at a specific spot just to get it running. Then you're supposed to use a scan tool to dial in the fuel sync perfectly. I never had a scan tool for OBD1, so I just used the method in the service manual and it ran fine. UT Awesome Marty describes that process in this video:
Here's the TSB procedure @fueliedart described. I eventually used this method to set my sync, and it ran fine either way. I redid the TSB method earlier this year when I was trying to see if that's why my car was running poorly (it was a bad O2 sensor). I have recently been wondering if with the change I made troubleshooting the O2 issue if it's off a little, because my fuel economy has been down ever since I touched it.
tcanin00
Well-Known Member
Thanks for explaining the problem you had and the repair. When I first put this engine in the car, I had a similar issue and someone suggested the TSB describing how to manually set the fuel sync like you mentioned. It ran much better after setting it. I have an older Snap On Solus that has the capability of setting the fuel sync. The OBD I PCM I had couldn't maintain steady base timing at idle, it would fluctuate 15* or so. Trying to electronically set the fuel sync made no difference, since the timing was all over the place.
After converting to OBD II, my scanner communicated once to show live data in a different format but will not communicate with the PCM now. I think it's because the scanner's battery won't hold a charge and loses power when going from key on to start.
Short story long, I agree with you in thinking the fuel sync is not set and is making it not run right.
tcanin00
Well-Known Member
Thank you for explaining your set up. Our exhaust systems are similar, and if yours is working properly I don't think having one O2 sensor in the right bank is causing the issues I'm having. I do think having an older O2 sensor could be the problem, so I might replace it later.
Yeah, this system is relatively crude in it's ability to make fuel trim adjustments based on O2 sensor input. The O2 sensor or sensors are more or less monitors of exhaust condition and catalytic efficiency.
I unplugged my O2 sensor because it was getting a trouble code for high signal voltage, and it ran just as bad as yours did. I thought the high voltage was from how the signal wire was routed when I had the harness apart. I rerouted it and still have the same problem. More troubleshooting to follow.
tcanin00
Well-Known Member
These are great resources to set fuel sync without a scan tool. They were suggested to me a while ago, and I used both to get my car running better.
I haven't moved the distributor since doing it. Wonder if I shouldn't recheck it since my scan tool isn't working right now?
Bobzilla
Well-Known Member
If you did the manual fuel sync method it should be close enough to rough decent. I have had my truck way off after replacing the cam sensor pickup in the distributor and it still ran the same. The sync is mainly used so the PCM knows where number one cylinder is, since the crank sensor runs on a symmetrical flex plate with no "missing tooth" like other more modern systems. With this system, on both OBD1 and OBD2 PCMs, you can actually start and run the engine without a cam sensor plugged in by jumping the wires for a random sync signal, and it still runs good enough to drive it home.
For the fuel pressure comments, understand that the PCM fuel map is set up to spray a certain quantity of fuel in a given amount of time that the injector is on. So if you change only the injector flow rate (different injectors) you spray an unexpected amount of fuel and the PCM has a hard time adjusting to that. Same thing happens any time the PCM flow rate does not match the injector flow rate, but also happens if the PCM and the injectors match but the actual airflow through the engine changes, like using a different camshaft or even a set of headers in some cases. That is when a custom tune is needed.
tcanin00
Well-Known Member
Thanks for posting all of this. It's nice knowing that I can find detailed information about the MPFI system that Chrysler used on this forum.
I came to the conclusion about the injectors based on what you said about set flow rates, duty cycle, dead time, and fuel pressure determined by the original tune. If anything is outside of spec, it won't operate correctly. Adjusting the pressure got it back into the range it needed. I think the 18.2 lb/hr injectors are being ran at a higher duty cycle than intended because the PCM is tuned for a 23.4 lb/hr flow rate.
The reason I converted to OBD II is the fact it is tunable for things other than stock components. My engine has a mild Comp cam, Hughes plane, and headers and it feels like the factory tune on both systems wasn't able to take advantage of those performance upgrades.
tcanin00
Well-Known Member
I did film a short video of accelerating onto the highway, and it didn't misfire or anything because it was being filmed. It did a couple of times afterwards, mostly on acceleration from an established speed.
tcanin00
Well-Known Member
Welp, I got the injectors. I should have known Chinese parts from Amazon are of questionable quality. Installed them and the car ran like garbage. I'm pretty sure at least one was stuck open and dumping fuel into the intake. They're on their way back to Amazon for a possible refund.
Put the old injectors back in and checked the IAC valve while I was at it. It had a decent amount of carbon around the cone and in the throttle body. Cleaned that up, put it back together, and it ran pretty good.
Figured I would drive it a bit, so I took it to my favorite on ramp. It still had a miss, but seemed to be running okay until it didn't. It felt like it was going into speed limitation and shut off. It usually starts back up after doing that, but didn't this time. Had it towed home. Now the fuel pump doesn't prime with the key on or while cranking. My scanner doesn't communicate, so I can't see what's going on.
Put the old injectors back in and checked the IAC valve while I was at it. It had a decent amount of carbon around the cone and in the throttle body. Cleaned that up, put it back together, and it ran pretty good.
Figured I would drive it a bit, so I took it to my favorite on ramp. It still had a miss, but seemed to be running okay until it didn't. It felt like it was going into speed limitation and shut off. It usually starts back up after doing that, but didn't this time. Had it towed home. Now the fuel pump doesn't prime with the key on or while cranking. My scanner doesn't communicate, so I can't see what's going on.
Bobzilla
Well-Known Member
Does the starter still turn the engine? Does it have spark?
tcanin00
Well-Known Member
Yes, the starter turns the engine. I haven't checked for spark yet.
Bobzilla
Well-Known Member
Check it out like it’s a stock truck. If you lost crankshaft sensor only, it will crank with the starter but will show no RPM on scan tool data and won’t have spark.
This could be a wiring issue, so if no spark you will unplug the crankshaft sensor and check the harness side of that connector. Pin 2 should be ground, so zero volts. Pin 3 is five volt reference, so it should read 5 volts, or pretty close to it.
If you have more than 0.2 volts on pin 2 start checking ground cable connections and power and ground to PCM.
If you have much less than about 4.5 volts on pin 3 start by unplugging other sensors using that five volt reference and see if the voltage on pin 3 comes back up to above 4.5 volts.
tcanin00
Well-Known Member
Thank you for the advice for troubleshooting. I'll check it out when I have time. To be honest, I have a lot going on and my car isn't that high on the priority list.
Bobzilla
Well-Known Member
Same here. Totally understand.
tcanin00
Well-Known Member
Had a chance to check it out today. There is 5 volts on both the 5V supply and the signal wire of the CKP on the harness side of the connector.
tcanin00
Well-Known Member
Was able to spend some more time troubleshooting. I thought it was weird to have voltage on the signal wire of the CKP, so I did some continuity tests on the harness to see if the 5v reference was in contact with the signal wire. It was not.
I decided to try the V6 PCM to see what would happen. It started and ran, poorly, but ran. It idled decent, but would not rev and popped out the intake whenever I tried to move the throttle. It reminded me of when this engine was in the Dakota. The previous owner had broken the CKP. It ran very similar then with a broken CKP to what it did with the V6 PCM.
I put the V8 PCM back, and it started and ran fine, it revved up fine. I let it run to operating temperature and checked the codes. There was nothing out of the ordinary, has a generic code for EVAP and a code for O2 signal high voltage. I wanted to test drive it, but it was getting late and I didn't feel like waiting for a tow truck if it quit again.
Short story long, I'm starting to think the CKP is going bad. I don't remember if I bought a cheap new one, or used one from a 1992 B250 van I got parts off of. I'll do some testing of the CKP cold versus hot and see if it changes.
I decided to try the V6 PCM to see what would happen. It started and ran, poorly, but ran. It idled decent, but would not rev and popped out the intake whenever I tried to move the throttle. It reminded me of when this engine was in the Dakota. The previous owner had broken the CKP. It ran very similar then with a broken CKP to what it did with the V6 PCM.
I put the V8 PCM back, and it started and ran fine, it revved up fine. I let it run to operating temperature and checked the codes. There was nothing out of the ordinary, has a generic code for EVAP and a code for O2 signal high voltage. I wanted to test drive it, but it was getting late and I didn't feel like waiting for a tow truck if it quit again.
Short story long, I'm starting to think the CKP is going bad. I don't remember if I bought a cheap new one, or used one from a 1992 B250 van I got parts off of. I'll do some testing of the CKP cold versus hot and see if it changes.
tcanin00
Well-Known Member
Have an update about something I found. I was reading posts on a Magnum group on Facebook, and a guy was asking for help with his truck that would shut off and not start back up when it got up to temperature. He was given good advice, and some things to check out, but he couldn't find the problem. He took it to a mechanic, and they found a bad ASD relay. He said the mechanic had the cover off the PDC and it was hot to the touch.
After reading that, I figured to check out my relays. I didn't find a bad relay, but I found that the fuel pump relay is not being grounded by the PCM consistently. Could be a problem in the PDC, the wiring, or the PCM itself. Have to do some more troubleshooting to narrow it down.
After reading that, I figured to check out my relays. I didn't find a bad relay, but I found that the fuel pump relay is not being grounded by the PCM consistently. Could be a problem in the PDC, the wiring, or the PCM itself. Have to do some more troubleshooting to narrow it down.
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