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1)Checking your problem in the driveway at idle or no load higher RPM will probably not reveal the issue since that is not when the issue occurs.
2)Your engine vacuum is low at 14/15" HG @ idle which usually indicates a Cam Timing issue.
We have encountered this issue numerous times on the site, one tooth off and...

3)You need to tape a fuel pressure gauge and vacuum/pressure gauge (tee'd into the FPR line) to the windshield and go for a ride (with a helper) and see what fuel pressure is reading when the problem occurs.
3A) You can also "deadhead" the pump to see if it is capable of providing fuel under all operating conditions.
Connect your fuel pressure gauge, start the car, momentarily pinch off the fuel return line.
Pressure should rise Instantly to 80-100 PSI.
If it does not, be sure there are no collapsed rubber lines, restrictions and if OK, replace the pump and strainer.
*MPFI maintains static pressure at the injector tip under all operating conditions, it is a combination of push (pressure) and pull (engine vacuum).
Static Rail Pressure (Key On Engine Off or engine idling with the FPR hose disconnected) = 53 - 57 PSI.
Engine Running W/FPR Connected, Rail Pressure will drop 1 PSI for every 2" HG applied to the FPR.
IE: Static = 55 PSI, start the engine and 18" HG is applied to the FPR, rail pressure will drop to 46 PSI, these numbers change constantly as you are on and off the throttle but static is always maintained at the injector tip.
When in boost, rail pressure should increase 1 PSI for every 1 lb. of boost.
IE: Static = 55 PSI, @ 12 lbs. of boost rail pressure should be at 67 PSI.

4)You could also have a problem with Detonation/Knock Retard", if the detonation sensor is seeing knock the controller will pull timing until the knock stops, you will probably not here the knock.
You need a scanner to view knock retard and total spark advance.
This happened to me a few years ago, me and my Son went out with the scan tool looking for info for another issue, under WOT the car would not go above 60 MPH, it basically just stayed at that speed with the pedal to the floor.
We switched to look at knock retard, total spark advance was at 0 with knock detected in #2 cylinder.
The issue was an "Ash" fouled spark plug, replaced the plug and the detonation issue was gone.
Fuel pressure and knock are related, if you are lean at higher RPM's, knock follows.

5)Check Map Sensor Calibration
The Map Sensor is the "Dominant Fuel Control Sensor" on the car, problems may be present but do not meet the criteria to set a code.
5A)You will want to connect a DVOM to the Map Sensor Signal and Signal Return Lines by backprobing the connector.
(Voltage translates to an actual pressure)
Then tee a Vacuum/Pressure gauge into the line between the Baro Solenoid and Map Sensor, run the meter into the passenger compartment and tape the gauge to the windshield, when the problem occurs be sure that Map Voltage = Actual Pressure (Manifold Vacuum) and that pressure to the Map is correct.
5B)When you first connect your meter before starting the car, turn the key on, read the voltage, this is the Barometric Pressure Reading, it should equal actual Barometric Pressure in your area.
 

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According to Chrysler you only need 100 PSI minimum on compression, my car was only 115.
Font Material property Parallel Rectangle Number

If you want to verify if the engine is the issue you need compression numbers and cylinder leakdown test numbers.

Also, I will state it again, Knock Retard, I had no idea how much power you can/will lose until it happened to me.
 

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Knock retard, how does the engine respond when it goes into knock retard? I know what the TD's feel like when they go into over-boost, immediately shutting down, pretty harsh IMO.
The car just falls on its face, no power, there is nothing violent about knock retard like there is with overboost shutdown.
When the knock sensor detects knock the engine controller will pull ignition timing on the cylinder(s) that has knock detected until the knock stops.
My Son and I went for a ride with his scanner (Snap-On MT2500), I do not remember exactly what we were looking for, however, I did take notes of sensor values at idle and after heat soak, so...???

With my foot to the floor in 3rd gear the car would not go over 60 MPH, it just stayed there at 60 MPH, like you were running into an extremely hard wind and you just could not go any faster, we tried 2-3 times with the same result.
(When racing I used to hit the traps in 3rd gear at 6100 RPM's/@88 MPH).
I said to him, bring up the knock retard and total spark advance screen, there we saw knock detected on cylinder 2 and total spark advance was 6 degrees BTDC @ WOT, when everything is OK total spark advance at WOT was 27-30 Degrees BTDC.
The issue was an "ash" fouled spark plug in #2 cylinder (been a problem for awhile, I usually just replace it every 6 month's.). See top row, 3rd pic to the right.
I replaced the plug and we went out again, this time with no knock retard/power problems.

Knock (Detonation) is caused by two things, excessive heat and/or excessive pressure (they are related).
Excessive heat in the cylinder(s) causes the remaining A/F mixture to ignite after normal combustion starts to take place, when this happens it is not a controlled burn and you have two (or more) colliding flame fronts which rattles the cylinder walls.
Detonation can be caused by low octane fuel (octane is the gasolines ability to resist detonation), lean A/F mixture, advanced ignition timing, deposits on the spark plug/top of pistons/valves, incorrect spark plug heat range, inefficient cooling system/deposits in the water jacket, inop EGR system (if equipped).
 

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You cannot read live data on any OBD1 vehicles, the baud rate between a scanner and our controllers is 1.25 seconds.
You can rent a fuel pressure gauge with a longer hose at AutoZone.
You leave a deposit and it is all returned to you when you return the tool.
 

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You still need to...
1)Verify Cam Timing is correct.
2)See if Map Voltage and Pressure are correct when the issue occurs.
3)See knock retard and total spark advance.
4)Check for exhaust restrictions or Air Intake Restrictions.

When I was at Jeep we had a customer that had purchased a used Cherokee.
His issue was that 45 MPH he lost all power and the vehicle would not go any faster.
The issue turned out to be that he placed a qt of oil underwood about 3" from the snorkel on the air cleaner box
The oil jug was being pulled right to the snorkel from engine vacuum and suffocating the engine, it also caused the hard plastic airbox to collapse from the vacuum and the snorkel being restricted.

You have to look at all charge piping to be sure you do not have a hose/tube collapsing at that speed where the issue occurs or any other possible restrictions.
 

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The only thing the factory had tee'd into the Map line from the manifold is the FPR, the boost gauge had its own dedicated line.
If vacuum/pressure is not bleeding off from the MAP sensor on decel then fuel and advance curves will be incorrect.
Instructions for checking MAP sensor calibration was posted in post #2.
 

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The HVAC is 1/8", 95 % of underhood is 5/32" and 7/32", the PCV system and some other lines off the air box may be/are a bit larger.
 

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All Chrysler coils on our cars are the same until they went to the epoxy filled brick style coils in 91.
1.2 - 1.6 ohms primary resistance.
9000 - 13000 ohms secondary resistance.
The "capacitor" you see is a "radio noise suppressor" which stops noise from the ignition system from coming through your speakers.
Ignition noise is static while alternator noise is a whirling noise.
 

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Popping/backfire from the intake manifold usually indicates Cam Timing is not correct or as I stated previously you are experiencing "knock retard".
Also, the lack of power issue could be related to an air intake restriction, exhaust system restriction or a fuel pressure issue.
If you verified that the ignition system is capable of 30 KVs at all four cylinders then ignition is not your issue.
 
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