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Hot rodded 318 vs factory OBD1 PCM

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Hot rodded 318 vs factory OBD1 PCM

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Old 05-21-2019, 11:48 PM
2ndTruck
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Smile Hot rodded 318 vs factory OBD1 PCM

Hello all.

Every time I am doing deep research for tech info on my truck, Dodge Forum keeps coming up so I decided to join.... Now onward we go.

1) Background on the truck engine: It is the original factory 5.2L (318) in it's last incarnation which gives it the "magnum" treatment (192K miles). It has been rebuilt and hot rodded by increasing the Compression Ratio to 9.5 to 1 through decking, replacing the cracked magnum heads with new EQ high flow heads with bigger valves, and replacing the cam with a Competition Cams longer duration higher lift roller unit. Not big enough to make it unstreetable but high enough to give a loapy idle and still have enough engine vacuum. Also purchased a Hughes (overly expensive) Air Gap dual plane manifold in place of the factory "kegger". Many internal parts were also replaced in the process. For exhaust I used JBA stainless steel ceramic coated shorty headers, JBA Y pipe, new converter, Flowmaster 44; one-in-two out exiting through Heartthrob cat back 2.5in pipes On the dyno the motor makes 368.1 ft-lbs of torque at 4700 rpm and 382.4 HP at 5900 rpm. I don't offer this information to gloat but only because it should be needed for tuning purpose discussion.

2) The problem: The engine will idle for maybe 2 min or so before dying. Hitting the throttle a little buys a little more time because it manages to get more air in but will eventually die anyway. Pulling a spark plug or two reveals they are getting gas fouled. While it is idling everything works including brake booster, power steering, and being able to creep the truck up and down the driveway (but don't go anywhere lest you get stuck!). Letting the plugs dry for 4 hours will allow me to to do it all over again. (at least it is consistently shi_ty!). Opening the throttle does nothing but try to kill the engine earlier as the idle circuit tries to compensate for the extra air.

3) Code and datastream analysis: For OBD1 you need an Actron CP9690 kit. I am using the original 2 barrel throttle body, original injectors (which I have read are good to 400HP), distributor and sensors. I do not have a Check Engine Light staying on but are getting codes out of it. After disconnecting the battery to clear the computer I read the code through the CEL and the scanner. 12 37 & 55 in that order; 12 is battery disconnect, 37 is not in the factory service manual but I get from the web is a misc solenoid, 55 is end of codes. The scanner says 37 (P0713) is trans temp?.

Now I start the motor. If I do not touch anything the codes won't change but if I crack the throttle I will get code 13 which is "MAP sensor does not see any change in manifold vaccum" On the scanner it is code P1297 which agrees. Again no CEL while running. I replaced the MAP sensor ($89 bucks!) and cleaned its throttle body orifice but it made no difference! I changed the MAP because I saw no change in sensor output voltage when my wife worked the throttle and I should have? TPS is working as I can vary that while looking at static datastream. Also I would not get a MAP sensor message if the PCM did not see the TPS moving.

For datastream values which basically do not change through the full recording time of the scanner (19 frames): Baro (HG) 25.8 and may go down to 23. It is running rich with injector pulse widths for 1 and 2 of an avg 11 ms (web says it should be 3 to 4 ms). MAP output voltage of 3.49V to 3.55V which is what I also read with a voltmeter. It is getting +5V and ground. MAP (HG) of avg 23.5. Spark advance of 18 deg (which from what I read is normal). Vacuum HG of 2.4.

For FYI the PCM does not have the engine in closed loop during this time since nothing but the headers ever gets hot and it dies in a couple of minutes. The service manual also has a complete discussion of PCM modes of operation. I learned this from an earlier theory that the exhaust leak I originally had on the passenger side y-pipe to header collector was causing the O2 sensor to richen the mixture. This is not true because the PCM is not using the O2 yet. Incidentally for anyone else thinking of this combination; The JBA y-pipe is NOT the correct pipe to connect to the JBA headers. The Y-pipe I ordered is an exact stock replacement; and it for sure is since it will fit the original manifolds and original converter pipe perfectly but NOT headers. I am going to have to go custom to fix this (more tools to buy).

It has a verified strong spark with the new MSD coil and Accel wires. But heavy gas smell coming out of that cylinder.

I am stumped but happy to be learning new stuff and I hate to have a problem beat me. I need to solve this and get it running right the way it is. (also wife is not happy) The Actron is able to upload to my PC making data uploadable to the web if anyone wants to look at all the data. Then I can continue upgrades. Maybe somebody can at least send me in the right direction. Thank you.

 
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Old 05-22-2019, 06:15 AM
93 ragtop
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Welcome to the forum!!

Hopefully, others with more knowledge will chime in, but until then, here are my thoughts,
1. The dyno numbers are stout!! I assume that was on a engine dyno, and not a chassis dyno?
2. If an engine dyno, was it, with a carb. or fuel injection?
3. What are the specs on the camshaft?
4. FWIW I dont believe the ODB1 systems can be custom tuned.
5. I believe you will need to do one of the following. Convert to OBD2, go aftermarket fuel injection, or convert to a carb.
 
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Old 05-22-2019, 08:01 AM
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Originally Posted by 93 ragtop View Post
Welcome to the forum!!

Hopefully, others with more knowledge will chime in, but until then, here are my thoughts,
1. The dyno numbers are stout!! I assume that was on a engine dyno, and not a chassis dyno?
2. If an engine dyno, was it, with a carb. or fuel injection?
3. What are the specs on the camshaft?
4. FWIW I dont believe the ODB1 systems can be custom tuned.
5. I believe you will need to do one of the following. Convert to OBD2, go aftermarket fuel injection, or convert to a carb.
This.

OBDI is not flash programmable.

For the running pig rich, it really shouldn't be doing that..... Take a look at engine coolant temp (what the pcm thinks it is) while running. Do the numbers look reasonable? Also have a look at fuel trims. See if they are seriously out of whack. Might also try running it with the O2 sensor unplugged, and see if that matters at all.

The MAP code really needs to be investigated as well......
 
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Old 05-22-2019, 10:06 AM
onemore94dak
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Three things things stood out to my novice eye
1. What year?
2. Fuel Synchronozation- did you do this after adding the cam? You cannot tune these motors but you can control when the injector dumps the fuel in the cycle.
3. The code is about the sensor reading not the temp of the trans. "Transmission temperature sensor detected no temperature rise after start. ** or Transmission temperature sensor voltage too low. ** or Transmission temperature sensor voltage too high. ** or
Relationship between engine speed and vehicle speed indicates no torque converter clutch engagement. ** or An open or shorted condition detected in the torque converter part throttle unlock solenoid control circuit. ** or Park/Neutral switch stuck in park or stuck in gear. **
* Check Engine Lamp (MIL) will not illuminate when this code is stored ** Check Engine Lamp (MIL) will illuminate when this code is stored *** Generator lamp illuminated
http://www.bionicdodge.com/Download/...uel%20Sync.pdf
There is a Mopar Performance PCM for the OBDI but they are like hens teeth. You will only be able to find used ones if you find one at all. Just saw one on JEGS and another on eBay. Being suspicious I wonder at how they word the listings. They are for the 92/93
 

Last edited by onemore94dak; 05-22-2019 at 10:14 AM.
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Old 05-24-2019, 12:22 AM
2ndTruck
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First to answer some questions.

1) Motor was run on an engine dyno. However I may be working with a tuner/emissions tech who has a chassis dyno.
2) It was fuel injected but using a shop Edelbrock RPM airgap manifold drilled for injectors. (almost the same as my Hughes)
3) The cam is around 0.470" lift and 270 deg duration
4) Engine is the original 1995. Last of the OBD1's.
5) Fuel synchronization could be an issue and I do need to investigate this further. That is adjusted by turning the distributor but I have to figure out the correct way to do it. I did initially set the distributor up according to the service manual.

One thing I forgot to mention earlier: Originally I thought I had a clogged fuel filter caused by dirt released when I pulled the fuel tank filler tube to drain the tank. I had replaced the fuel pump at 168K miles. But I was wrong - the tank and filter are very clean. Before I reconnected the fuel line I ran the pump to clear the line. Then put a fuel pressure gauge on the fuel rail. Reads 38 psi even when running and takes 4 hours to bleed down. With no leaks. So it is good.

I have thought about different conversions. This is the last of the EGR engines and I was trying to keep the truck emissions legal even though we don't have emissions up here. But there is no longer an EGR manifold (other than the kegger) available for the 5.2/5.9 so I lost emissions anyway. In 1996 Dodge managed to do away with the EGR under the new OBD2 system. So an OBD2 conversion would be the best way to go for me. But I would not replace an entire harness. I would compare schematics and wiring diagrams of the two systems to see where I would have to rewire to setup a 96 PCM.

Holley, FAST, Big Gulp aftermarket systems are another way to go because I can use all the original sensors but with a new 4bbl throttle body.

Will try disconnecting the O2 sensor and both CTS sensors but especially investigate the fuel sync issue.
 
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Old 05-24-2019, 07:13 AM
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If you decide to switch to OBD2, I think it would be easier to swap the entire harness, and just repin the stuff for what goes to the dash.... a LOT less work that way.
 
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Old 05-24-2019, 10:51 PM
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Give this thread a look. It has a manual method of setting fuel sync if you don;t have a scanner. the guy had a 318 he put a cam in too.It's 6 years old so some of the places they link may no longer do what they did.

Edit-I forgot to post the link here. I am adding it in case a search lands on this post https://dodgeforum.com/forum/2nd-gen...-tuning-4.html
 

Last edited by onemore94dak; 05-25-2019 at 10:03 AM.
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Old 05-25-2019, 12:44 AM
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Do not see a thread link in the previous post. Also the truck is a 1995 - never answered that question. Trying some things tomorrow and looking into AEM, FAST and SCT overlay computers. But I would think that the original PCM would at least be able to run the motor? Thanks.
 
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Old 05-25-2019, 08:23 AM
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Originally Posted by 2ndTruck View Post
Do not see a thread link in the previous post. Also the truck is a 1995 - never answered that question. Trying some things tomorrow and looking into AEM, FAST and SCT overlay computers. But I would think that the original PCM would at least be able to run the motor? Thanks.
It should run, but, it won't run very well. Too many changes that the PCM has no clue about.
 
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Old 05-25-2019, 10:02 AM
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https://dodgeforum.com/forum/2nd-gen...-tuning-4.html
You dud mention the year in post #5
 

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