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Unread 02-17-2014, 02:49 PM   #16
Boothe
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Status Update: Per Que89YJ I replaced the spark plugs with Champion Double Platinums gapped to .035". Then I checked the spark and have good strong spark at #4 plug. I checked it at #3 the other day and it was strong there too. The spark will jump over a 1/4" when connected to the spark gap tester; I don't see a problem there. I could smell gas at the exhaust pipe, so I figure the fuel injectors must be spraying. Which seems to bring us back to a timing problem.

Anyhow, I hooked the AutoXray scanner up to it and attempted to start it again while monitoring live data. Here's what I found:

01 O2 Bank 1 / Pos 1 = 0.49 volts
02 Coolant Temp = 41.0 F
03 Coolant Sensor = 3.5V
04 Throttle Pos = 0.6V (this does vary from 0.6 - 3.4 V with the accelerator pedal)
05 Min Throttle Pos = 1 V (now this one does pique my interest, because if the minimum throttle position is 1 volt and I'm getting 0.6V, perhaps that's a red flag. Comments?)
06 Battery Voltage = 12.2 V
07 MAP Sensor = 29.4 in-Hg
08 AIS Position = 140 Steps (Can anyone tell me what this parameter is?)
09 Adapt Fuel #1 = -1024 us (microseconds)
10 Adapt Factor #1 49.9%
11 Baro Pressure = 29.4 in-Hg
12 Engine Spd = 0 RPM (this went up to 128 RPM while cranking, indicating a good crank position sensor)
13 F1 Start Counts = 0 Starts (?)
14 F2 Start Counts = 0 Starts (?)
15 F3 Start Counts = 0 Starts (?)
16 Module Advance = 0.0 deg. BTC (does not change when cranking)
17 Charge Temp = 44.6 F
18 Charge Temp Sens = 3.4 V
19 Cruise Target = 0 MPH
20 Speed Control = Disabled (consistent with no cruise control on my vehicle)
That was all the live data parameters listed.

I'll pick up a throttle position sensor and see if that helps, since the voltages the PCM is seeing are consistent with what I found with my Fluke 87V: low. After that, I guess it goes back to the PCM connector and wiring like Why J? suggested above.

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Unread 02-17-2014, 03:14 PM   #17
Why J?
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Did you replace the distributer in this ?

If so are you sure it's not 180 out?
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Unread 02-17-2014, 04:33 PM   #18
Que89YJ
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You have spark and fuel to the cylinder. The only reason it won't start is because they are arriving at the wrong time. The tps is not so far off that it is short or open. You have a timing issue. You need to check the timing.
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Unread 02-18-2014, 06:12 AM   #19
Boothe
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Que89YJ - Thanks for the tip. A timing problem was more or less the conclusion I came to as well. Now here's my concern: According to the FSM, timing is determined by the PCM looking at crank position. In other words, distributor position has no bearing on it. The FSM even warns not to remove the tab that indexes the distributor to the bolt hole in the block, because it won't make any difference since spark timing is determined by the crank position, not the cam position. If that's true, the only ways the timing could change are if the PCM has lost its input (or lost its mind) and is adjusting the timing wrong. It sees RPM so I don't see a problem with the CPS input. Or the other option is that the timing chain has jumped a few teeth (a scenario I really didn't want to entertain). If the chain had that much slack, I suppose it could have jumped and then as it ran jumped some more, until finally it wouldn't restart. It never "dieseled", popped or backfired, it had no power like the timing was retarded, then wouldn't start.

Does the 4.0 have a fiber timing gear like some of the GM motors?

Is the 4.0 known to have a problem with the chain jumping time?

I suppose at this point I need to pull the valve cover and the #1 plug, find TDC on the compression stroke and see where the distributor is pointing...
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Unread 02-18-2014, 07:04 AM   #20
Mark05059
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Quote:
Originally Posted by Boothe View Post
Que89YJ - Thanks for the tip. A timing problem was more or less the conclusion I came to as well. Now here's my concern: According to the FSM, timing is determined by the PCM looking at crank position. In other words, distributor position has no bearing on it. The FSM even warns not to remove the tab that indexes the distributor to the bolt hole in the block, because it won't make any difference since spark timing is determined by the crank position, not the cam position. If that's true, the only ways the timing could change are if the PCM has lost its input (or lost its mind) and is adjusting the timing wrong. It sees RPM so I don't see a problem with the CPS input. Or the other option is that the timing chain has jumped a few teeth (a scenario I really didn't want to entertain). If the chain had that much slack, I suppose it could have jumped and then as it ran jumped some more, until finally it wouldn't restart. It never "dieseled", popped or backfired, it had no power like the timing was retarded, then wouldn't start.

Does the 4.0 have a fiber timing gear like some of the GM motors?

Is the 4.0 known to have a problem with the chain jumping time?

I suppose at this point I need to pull the valve cover and the #1 plug, find TDC on the compression stroke and see where the distributor is pointing...
no need to pull the valve cover.. pull #1 plug.. turn the engine using the crank bolt with your finger on the hole. When you feel compression you need something to put into the plug hole (wooden dowel, screwdriver) so you can see exactly when its at the top. Then remove your distributor and see where your rotor is pointing.
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Unread 02-18-2014, 07:21 AM   #21
Que89YJ
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Exactly what mark said. There is a possibility the distributor gear is warn or the chain jumped a tooth. I cant think of any reason for an engine that is getting fuel and spark to not at least try and start unless the timing is off.
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Unread 02-18-2014, 08:38 AM   #22
Boothe
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I found this thread on checking the timing chain without pulling the cover: http://www.jeepforum.com/forum/f19/t...mileage-13030/ I'll give that a try as well. At 161K, it's due for a check anyway.
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Unread 02-18-2014, 09:23 AM   #23
Que89YJ
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That is to see if it is stretched. The timing is a little different. You can just pull the distributor cover and look at the rotor. Use a wrench on the crank bolt and turn it until the rotor starts to move. Stop and turn it in the other direction. Anything more then 1/2" movement before the rotor moves is bad. That tells you if the chain is loose but not if its jumped.
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Unread 02-18-2014, 08:47 PM   #24
Boothe
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Status update: I brought my good friend and Mopar guru over so we could put our heads together on this problem. He told me earlier today he suspected the engine was flooded. We attempted to start it and then pulled a couple of spark plugs and they were wet. He had me pull the fuel pump relay and try to start it again. Sure enough after quite a bit of cranking the engine tried to start. Not just the occasional pop or cough, but it actually started and tried to run! At that point we put the scanner back on the diagnostic connector and checked MAP function. MAP pressure stayed at 29.4" Hg even when cranking. So the next thing we did was pull the vacuum line off the MAP, connect a hand vacuum pump and checked MAP function with the key on. We ran the vacuum down to -15" Hg and -28" Hg with no change in output signal. So I pulled the MAP and it's a GM part. Weird.

I'll pick up a new MAP sensor tomorrow afternoon and swap it out. We'll see if that fixes the problem.

Last edited by Boothe; 02-19-2014 at 07:33 AM..
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Unread 02-19-2014, 11:10 AM   #25
Why J?
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Quote:
Originally Posted by Boothe View Post
Status update: I brought my good friend and Mopar guru over so we could put our heads together on this problem. He told me earlier today he suspected the engine was flooded. We attempted to start it and then pulled a couple of spark plugs and they were wet. He had me pull the fuel pump relay and try to start it again. Sure enough after quite a bit of cranking the engine tried to start. Not just the occasional pop or cough, but it actually started and tried to run! At that point we put the scanner back on the diagnostic connector and checked MAP function. MAP pressure stayed at 29.4" Hg even when cranking. So the next thing we did was pull the vacuum line off the MAP, connect a hand vacuum pump and checked MAP function with the key on. We ran the vacuum down to -15" Hg and -28" Hg with no change in output signal. So I pulled the MAP and it's a GM part. Weird.

I'll pick up a new MAP sensor tomorrow afternoon and swap it out. We'll see if that fixes the problem.
Good deal.
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Unread 02-20-2014, 10:12 AM   #26
Boothe
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I put the original MAP sensor on the bench yesterday evening. I connected 5.0 VDC to pin C, power supply negative to pin A and a DMM to pin B. We pulled as much as -20" Hg on it with a Fluke hand pump calibrator and watched it go from 4.96 V down to 0.7 V with vacuum applied. Now, I did drop the sensor prior to testing it, so if something was stuck inside that may have freed it up. But not trusting it, since it appeared to be failed a couple of days ago and is 21 years old (heck it could legally drink & vote!), I picked up a new one on my way home. I installed the new MAP, put the AutoXray on the PCM and cranked the engine. The sensor responded to the changing manifold vacuum showing 3.4" Hg key on, then dropped to 2.9" Hg cranking. I don't know if those values are correct since I don't know the actual calibration range, but at least the numberrs did change in the PCM. And the engine did try to fire, but there was no fuel pressure on the rail so I reinstalled the fuel pump relay. When I tried to start it again, it was back to the same problem apparently; engine flooded / no start. I ran out of time, so I'm going to check the injectors, wiring and the PCM this evening. The only thing I can figure is that I either have an injector stuck open (which I doubt since it took quite a while for fuel pressure on the rail to drop when I checked it a few days ago) or I have a grounded injector dumping raw fuel into the manifold when the key is on. Any thoughts?
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Unread 02-20-2014, 05:05 PM   #27
Que89YJ
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I stand by what I said. Timing is it if you have fuel and spark. The book tells you based on the crank cam being in the right place the timing is controlled by the ecu.
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Unread 02-20-2014, 05:42 PM   #28
Mark05059
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lets stop all the dicking around.. Pull #1 plug out.. with a socket on the crank bolt and your finger stuck in the spark plug hole, turn the engine over until you feel compression on your finger. Then put something in the hole (screwdriver, dowel, etc) and continue moving the crank till it stops. Remove the distributor cap. Is the rotor pointing at #1 plug?
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Unread 02-20-2014, 08:19 PM   #29
Boothe
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Uhhh...Mark05059....we already did that. I hate to tell you but the timing is okay. Sorry dude, it's flooded. What messed me up is flooding is something I haven't seen since my last vehicle with a carburetor on it. I went out again this evening and tried to start it without letting the fuel pump have two seconds to pressurize the rail. And it fired (no popping, no backfire) and then died. I was watching the MAP data live on the AutoXray. It started out at 3.4 "Hg, dropped to 2.4" Hg cranking, then went to 10.2", then when I tried again 7.5". The MAP sensor is all over the board. I'm an Instrument & Controls tech by profession and I'm here to tell you that pressure transducers don't typically behave this way unless something's wrong. It's a wiring / connection issue I'm guessing. But I didn't have time to really dig into to it tonight. Maybe this weekend...
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Unread 02-20-2014, 09:03 PM   #30
Que89YJ
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Cool, then you got a handle on control systems. The flood clear on all injected vehicles is wot. Pushing the pedal to the floor cuts out the injectors. You have spark and note you have flood. You checked your fuel pressure but you didn't check bleed down time to see if you are dumping fuel into the cylinders. Check to see if you are holding above 20 psi. There is no reason to flood unless the tps was not telling the ecu you had the pedal to the floor.
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