Dead MAP sensor?

[Double-A]

So still working on getting my turd running after the engine fire 9 years ago. Don't judge.

Been chasing a gremlin off and on for the past 8 years (more off than on) and think I may have found it - just looking for confirmation from people smarter than me.

It has no codes, but runs pig-rich, stumbles on acceleration, and the boost gauge (dash) doesn't move. Swapped in a different cluster and that boost gauge didn't move either. After a visual check of the DRAC wires (look fine) I figured I'd check the 3-bar MAP.

From what I've read, the "easy" way to check the sensor is check voltages on the green wire - should be 5v. I got a solid 4.44v (my battery charge may be a bit low, or could be the odyssey battery) so I hooked a vacuum hose to the sensor and sucked/blew into it looking for the voltage to drop. No voltage change at all. I'm assuming that means the sensor is fubar, but before blowing $80 on a new one (and continuing to blindly throw parts at it) I thought I'd confirm.

Thanks!

 

[DaveP]

Re: Dead MAP sensor?

I figured I'd check the 3-bar MAP.

From what I've read, the "easy" way to check the sensor is check voltages on the green wire - should be 5v. I got a solid 4.44v l. I'm assuming that means the sensor is fubar, but before blowing $80 on a new one (and continuing to blindly throw parts at it) I thought I'd confirm.

I don't think your MAP is faulty. A 3bar MAP should have ~1.65V on the green wire with engine not running. Not 5 volts.

First confirm the proper wiring to the MAP

Pin A = black = sensor ground.
Pin B = green = output to ECM.
Pin C = grey = 5 Volt reference voltage from ECM.

With key on, engine off, MAP sensor connected, back-probe the connectors with your VOM. You should get the following:

Pin A to C = 5 volts
Pin A to ground = 0 Volts. If no, the ground is open, sensor is not grounded, and this is your problem.
Pin C to ground = 5 Volts. If no, this wire is open to ECM. (Not your problem, you have 5 Volts).
Pin A to B = 3 bar, 1.65 Volts. 2 bar, 2.5 Volts. 1 bar 5 volts.
Pin B to ground = same as above. If no, and voltage = 5.0, no ground on pin A. If voltage = O, no 5 volt on pin C.

I don't think your sensor is grounded through pin A. Check that first.


Odd that you're not setting codes. MAP at 4.5V engine idling should be setting a code 33.

Unless this is a TurboTweaked-up chip. Eric changes the parameters for the DTC's and no one other than him has any idea what will set the DTC's. I don't know why he changes them. It makes the DTC's useless for diagnosing electrical problems. Which is what the DTC's are for. to make things easier for peeps that know how to use the DTC's. Changing the parameters from published, ESTABLISHED specs is frustrating because it nullifies a very effective system for diagnosing electrical problems because the new parameters are unknown, and usually the fact that they have even been changed in the first place ( by Eric) is unknown. It was a surprise to me when I learned this last week in another thread where the guy pulled his hair out for months because all that had changed were the parameters for setting the code he was getting. Turns out there was nothing wrong with the guy's truck, just a crappy DTC sub-routine for the code he was getting.

Regardless of the chip, you should have 1.65 volts on the green wire, key on engine not running for a 3 bar.

 

[Double-A]

Re: Dead MAP sensor?

Thanks for the huge help Dave! :tup:

First confirm the proper wiring to the MAP

Check.

With key on, engine off, MAP sensor connected, back-probe the connectors with your VOM. You should get the following:

Pin A to C = 5 volts
Pin A to ground = 0 Volts. If no, the ground is open, sensor is not grounded, and this is your problem.
Pin C to ground = 5 Volts. If no, this wire is open to ECM. (Not your problem, you have 5 Volts).
Pin A to B = 3 bar, 1.65 Volts. 2 bar, 2.5 Volts. 1 bar 5 volts.
Pin B to ground = same as above. If no, and voltage = 5.0, no ground on pin A. If voltage = O, no 5 volt on pin C.

I don't think your sensor is grounded through pin A. Check that first.

A to ground = 0v
B to ground = 4.4v
C to ground = 5v
A to B = 0.5v
A to C = 0v

And checking continuity A to ground, no continuity, so your assumption seems correct. Forgive me, I'm electricity-impaired.

I assume I can back-probe the grounds on other sensors (MAT, TPS on circuit 155) for continuity to verify grounds from the ECM are good, as well as back-probe the 452-circuit coming out of the ECM to verify ground is "going into" the wire itself.

I think this is right:
- Good ground at 452/ECM tells me the wire is bad.
- No ground at 452/ECM but good ground at 155/ECM tells me the ECM is bad.
- No ground at either 452 or 155 tells me my ECM ground is bad.

BTW - it's a Dig chip, so I'm assuming that is not an issue.

I'm also assuming (from the wiring diagram) that 413 tan is the ECM ground from the back of the back of the driver's cylinder head, so I should be able to back-probe that as well. FWIW I have good continuity between negative terminal, firewall ground and intake ground, so the body and engine seem to be well grounded and I should be able to get good ground off the back of the head and from the interior when checking the ECM.

Guess I'll get back to my back-probing. Please correct me on anything I may have screwed up, and thanks again.

 

[DaveP]

Re: Dead MAP sensor?

I assume I can back-probe the grounds on other sensors (MAT, TPS on circuit 155) for continuity to verify grounds from the ECM are good, as well as back-probe the 452-circuit coming out of the ECM to verify ground is "going into" the wire itself.

I think this is right:
- Good ground at 452/ECM tells me the wire is bad.
- No ground at 452/ECM but good ground at 155/ECM tells me the ECM is bad.
- No ground at either 452 or 155 tells me my ECM ground is bad.

Coolness. You're making progress. There's no ground at the MAP. Your assumptions are correct.
Bad wire, bad connection at ECM, or bad connection at MAP.

The Coolant Temp sensor shares the same ground cir 452. You might check the black wire at the CTS for continuity to engine block. It should be open as well, if it is a wire or ECM connector related problem.

One thing to check at the ECM connectors. I've had the metal connector fracture inside the plastic block. So continuity was intermittent. Take each wire and push / pull on it from the wire side while observing the metal connector on the ECM side. If you find a wire that moves, but the ECM side does not, it's broken internally.

I still don't understand why your not setting Code 33, (and Code 15 if the CTS is also affected) unless you also have a TPS voltage problem and the TPS is >2%, which won't allow the Code 33 diagnostic to run. Check your TPS voltage key on engine off, the same way as MAP. Black to blue at the TPS should be ~.5 Volt at closed throttle. If it's higher, you will have to run the diagnostics on the TPS ground like you did for the MAP.

I think the tan/wht cir 551 at the front of the intake manifold is the sensor ground. But I'm not sure. The big black at the front of the intake has nothing to do with the ECM. But the tan/white does. So there are 3 grounds associated with the ECM. The 2 at the back of the head, and the tan/wht at the front of the intake.

You obviously have the Helms manual with wiring diagrams. Unplug the ECM, do the connector test I suggested above, then check the individual ground pins for continuity to engine block. I see A12, C13, D1, D7, E15 are all grounds to engine block.

Now that you understand what the problem is, you should be able to find it pretty quickly. Check the TPS ground too. If TPS is also affected, then check the ECM ground pins or wires.

Regarding lack of Codes: Check pin C16 orange wire for 12 volts at all times. This is the memory wire. If voltage is not present at this connection, Codes will be 'lost' when key is turned off.

You're doing great. You'll track it down.
:tup:

 

[neildemo]

Re: Dead MAP sensor?

Another great Article from our Godfather of Sytys Dave P. Definetly a Vault item!

 

[RealFastV6]

Unless this is a TurboTweaked-up chip. Eric changes the parameters for the DTC's and no one other than him has any idea what will set the DTC's. I don't know why he changes them. It makes the DTC's useless for diagnosing electrical problems. Which is what the DTC's are for. to make things easier for peeps that know how to use the DTC's. Changing the parameters from published, ESTABLISHED specs is frustrating because it nullifies a very effective system for diagnosing electrical problems because the new parameters are unknown, and usually the fact that they have even been changed in the first place ( by Eric) is unknown. It was a surprise to me when I learned this last week in another thread where the guy pulled his hair out for months because all that had changed were the parameters for setting the code he was getting. Turns out there was nothing wrong with the guy's truck, just a crappy DTC sub-routine for the code he was getting.

When you've got a modified vehicle with an aftermarket chip you accept the fact that factory troubleshooting methods and data may not work.

Your very public dig at Eric is unnecessary and added very little to the conversation.

 

[DaveP]

Re: Dead MAP sensor?

Your very public dig at DaveP is unnecessary and added nothing to the conversation.

There, fixed it for you.

 

[Double-A]

Re: Dead MAP sensor?

OK, progress may have been made.

Good ground at all ECM points mentioned. Good ground also at the CTS, so I've deduced that the ground wire is bad somewhere between the split point for the CTS and the MAP. (It's a used replacement harness, so who knows...) I snipped the black wire a few inches from the MAP and jumped it to the known good firewall ground by the brake booster for the time being. 1.52v jumping B to A on the MAP - a definite improvement. Decided to start it up, and...

not so great. Started harder, although battery might be a little low on charge from repeated "key on" testing. Boost gauge finally moves, but is backwards - under idle the needle is halfway into boost, rev engine and the boost gauge drops into vacuum. Very wet on ground behind tailpipe, and very noticeably rich - stumbles consistently under throttle, likely due to too much fuel if I was to guess. Idle is still high (did I mention that?), I'm guessing also due to too much fuel. Maybe those are bad guesses.

The fact that the boost gauge moves and I have almost correct voltage at the B pin on the MAP tells me that seems to have fixed an issue, but why/how in the hell is it reading boost/vacuum backwards?