How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Juan Crespo Your Own Question
Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Jeep
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
Type Your Jeep Question Here...
Juan Crespo is online now
A new question is answered every 9 seconds

Story short, customer requested refurbished heads with new

Customer Question

Long story short, customer requested refurbished heads with new timing components. One of my mechanics performed the repair with repairs to the heads and all new timing components. vehicle started upon completion but it ran exteremly rich, & and smelled like bad catalytic converters. When I pulled up the graphing data on the scan tool I noticed something very interesting. It's displaying a current sync (2) that's switching back n forth between ok & sync lost with only the ignition on. Current Sync (1) is a solid OK. Replaced cam & crank sensors with no change. What else I noticed was interesting was the MAP sensor is reading 3.7v, coolant volts @ 4.5v, IAT @ 4.98, left & right exhaust reading rich, all 4 oxygen sensors (this is a California model) reading around 4.9v, oil pressure @ 4.57v, sensor reads 70psi when unplugged pressure goes to 0 but still reads 4.57v on graph. All these readings are with engine off ignition on. Vehicle struggles to keep running and the cats get exteremly hot after running for a short amount of time. Has the sulfur smell to it. No codes are coming up at this time. Thinking maybe a wiring issue?
Submitted: 1 year ago.
Category: Jeep
Expert:  Juan Crespo replied 1 year ago.

Do you still need help with this?

Customer: replied 1 year ago.
Yeah please :). No access to wiring schemitcs right now and it's driving me a little crazy haha
Expert:  Juan Crespo replied 1 year ago.

Well, I would also go crazy looking at those screens. Sometimes we need to take a step back and regroup. So let's do that, shall we?

We know the engine starts and runs, so we can eliminate all the systems and components asocciated with that function. What we have left is an engine running rich and a lot of weird data from the PCM.

Out of all that weird data, one jumps at me as being particularly weird, and that is O2 voltage at 4.9 volts. In my experience, I've only seen that happen in vehicles where the O2 harnesses had been touching the hot exhaust pipes. So, were I in your shoes, I would put that Solus down and start checking those harnesses. If those check out OK, and you might have to pull out your Ohmmeter to verify they are indeed OK, then keep going through all the sensor circuits starting at the sensors themselves and all the way up to the PCM.

It is highly probable that the problem is in the wiring, but if every circuit tests out OK, then I would have to say the computer is shot - it's just that I haven't seen many computers going bad on their own, if you know what I mean ;-)

This one seems to be challenging, please let me know what you find.


Remember that what you see on graphing scanner screen is just an interpretation of the signals being sent by the onboard computer. The actual signals, may they be in from a sensor or out to an actuator, can only be accurately checked at their source with a meter or scope.

Customer: replied 1 year ago.
Sounds great, in the morning I'll go ahead and do a close check of the oxygen sensor wires around the exhaust pipes. I'm gonna go ahead and peel back the sleeve to ensure nothing is burnt :). I'll let you know tomorrow!
Expert:  Juan Crespo replied 1 year ago.

Looking forward to reading something like "I found it!!!" from you tomorrow.

Best Regards.

Customer: replied 1 year ago.
Sorry for the delay. Last week got busy, back at it today! I'll let you know.
Customer: replied 1 year ago.
Took a peek around the exhaust for any burned wires, no luck. Peeled back the wire loom around the exhaust manifold in hopes of finding something around that. But the wires in that particular area look ok. What should I go after next?
Expert:  Juan Crespo replied 1 year ago.

If you've checked all the wiring and connectors and found no opens or shorts, then the PCM must be the problem.

Customer: replied 1 year ago.
Is this vehicle able to have a used pcm installed? Could you send me a wiring schemitc of the oxygen sensors (California model). I've done a visual inspection but I'd like to check everything with a ohm meter.
Expert:  Juan Crespo replied 1 year ago.

Starting with MY 1999, PCMs need to be programmed.

I've attached the O2 sensor circuits for the California model. When checking wiring, don't forget to look closely at the PCM connectors for any corrosion or debris.

Customer: replied 1 year ago.
What all wires should I check @ the pcm, can you give me wire color & cavity location for everything? I don't want to just throw an expensive pcm at this without actually seeing the issue being in the computer.
Expert:  Juan Crespo replied 1 year ago.

I don't quite understand what you're requesting; the circuit diagram I previously uploaded for you shows wire color, PCM connector and terminal numbers. For example, O2 sensor 2/1 signal goes to PCM connector C1 terminal 25 on a Tan/White wire. If that is not what you need, or if you need anything else in addition to that, please let me know and I'll try to get it for you.

Customer: replied 1 year ago.
I'd like to get the wiring schemitcs for all the other sensors that aren't reading correctly. Check the attached pictures from the first post, like oil pressure intake air temp, engine coolant, manifold pressure, etc. anything that's reading abnormal. What should the specs of these sensors be with ignition on, and what readings should I get on each wire for the sensor.
Expert:  Juan Crespo replied 1 year ago.

I can certainly get you all that information for an added fee. Please accept the Premium Service Offer and I'll get to work on it right away.

Expert:  Juan Crespo replied 1 year ago.

Since it looks you're not accepting my proposed service, I'll opt out so others may try to help you. Do not reply until another expert responds or the site will cycle the request back to me.