Turbo Dodge Forums banner
1 - 13 of 13 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter · #1 ·
Hi everyone,

French dude here working on a 1992 Daytona 2.5L T1.
It's been two years since I got this car and started working on it.

I changed/restored/checked almost everything, spark plugs, wires, pressure line regulator, the whole hose system, etc...
Using it as a daily driver, it worked quite good for a month.
It suddenly started misfiring and even pseudo-stopping.

Let me explain:
At 70+ km/h everything is OK.
Pressure builds up properly at any speed, and the waste gate does its job perfectly.
Problems appear when driving "slowly".
Under 70 km/h, releasing the accelerator pedal causes misfires.
At even slower speeds, the motor rarely stops, but restarts a few seconds after.

All of these misfires only occurs on charge as pressing the clutch pedal stops misfires instantly.

Please share any insights, I have no clue left to check for faulty parts.
Thanks in advance!
 

·
Administrator
Joined
·
26,073 Posts
70 KM's = 43 MPH which is not excessive speed.

Is this an actual misfire or a stalling on deceleration issue?
Just want to be sure we are on the same page.
A misfire is fuel and air enter the combustion chamber, no combustion takes place and the same fuel and air exit through the exhaust, basically you are losing one or more cylinders when this happens.
A misfire during deceleration only is a rare occurrence, usually a misfire is always present or present during acceleration/load. Decel is a very lean/no load/fixed program operating mode.
A misfire can be caused by numerous things that would need to be checked/diagnosed to be sure they are OK.
At this point to locate the cause of the misfire you will have to forget the fact that you have newer parts installed, new does not always = good and they have to be viewed as such.
You have to assume during diagnostic that the cause could be from anything Ignition/Fuel/Engine Mechanical/Vacuum System/Exhaust System/Sensor Issue, etc. could be causing the misfire.

1)Does the vehicle backfire when the misfire occurs?
a)If Yes, is the backfire coming from the intake manifold or exhaust?
2)Is there any smoke (Black, Blue, White) when the misfire occurs?
3)Are any spark plugs showing signs of fouling.
a)Spark plugs are your eyes into what is happening in each cylinder.
4)Are any fault codes stored in memory?
5)On decel, what is your boost gauge reading?
a)When you release the throttle, engine vacuum should increase to at least 20" HG.

Post Back and we will go from there.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #3 · (Edited)
Thanks for your detailed reply.
I think there's a misunderstanding and/or mistraduction from my side.
By misfires I mean that I hear kinda loud explosions from the exhaust line. The correct term is backfire if I correctly understand.
I do not lose any power when it explodes tho.
So:
1) I'm pretty sure it backfires, not sure if it misfires as there's no significant RPM loss.
2) No smoke in sight
3) I check and replaced spark plugs, I looks like it runs a bit rich as needed (I understood this engine runs a bit rich but I may be wrong)
4) I never checked fault codes to be honest. I'll take a look asap
5) It depends (and needs to be verified, but as I remember) :
  • releasing the accel pedal a bit makes the gauge turns to a bit below 0 psi
  • releasing the accel pedal totally makes the gauge turns to max depression, almost as much as on idle
Disengaging the clutch does not provoke any backfire. It only happens during "motor braking".

Please tell me if you need more information or if I'm not clear enough.
Thanks for your help!
 

·
Administrator
Joined
·
26,073 Posts
These cars/engines do run rich from the factory, it is for engine safety (rich is safer than lean) and is not rich enough to cause any driveabilty issues, there should not be any fouling of plugs.
If you are hearing a backfire through the exhaust on decel you are rich.
On decel the system goes "Lean" since engine vacuum increases and there is absolutely no load, excess fuel is not needed.
If you are rich on decel the combustion is taking place in the hot exhaust, hence the backfire.
Rich can be caused by numerous things...
1)Ignition System
I do not think ignition is your issue since the problem only takes place during a no load condition, if the ignition system were causing the issue it would more than likely happen under load when KV requirements increase.(Kilovolts, Voltage needed to have amperage flow from the coil to the spark plugs and jump the gap to ground, as load increases KV requirements increase, 10-15 KV @ idle, 25-30 KV @ WOT/Full Boost)
2)Fuel Pressure
a)If Fuel Pressure is high or the Fuel Pressure Regulator is leaking you will be rich.
b)Remove the vacuum/pressure hose from the FPR, look for raw gasoline in the hose.
c)Checking Fuel Pressure
3)Leaking Fuel Injector(s)
a)If you have a quick leakdown of fuel pressure (See "Checking Fuel Pressure in step #2) with the engine off this will need to be checked, this will require removal of the fuel rail and injectors to check.
4)MAP Sensor Calibration
a)The MAP Sensor (Manifold Absolute Pressure) is the "Dominant" Fuel Control sensor on the vehicle, if its calibration is not correct or it is not seeing the proper vacuum/pressure fuel control will be off.
5)EVAP System (Rollover Valve In Fuel Tank, Vapor Canister, Purge Solenoid)
a)If there is an issue with the EVAP (Evaporative Emissions Control System) and fuel vapors are being allowed to enter the engine on decel you will be rich.
6)Oxygen Sensor Switching.
a)This will allow you to see exactly what is happening with the fuel control system.
b)The O2 Sensor is a fuel trimmer, it is used to bring fuel control during "closed loop" operation (Idle and no load cruise) into a tighter range for fuel economy and to lower CO emissions.
c)The engine controller attempts to keep the A/F ration at 14.7/1 (Stochiometric) during closed loop operation.
d)When exposed to oxygen in the exhaust system the O2 Sensor through a chemical process produces a small voltage, .1-.9 volts with .450 volts being 14.7/1. The engine controller through small fuel corrections attempts to keep the A/F at 14.7/1. If the voltage is below .450 (lean) the controller will add fuel, as this happens the voltage will go above .450 volts (rich) and this constant adding/subtracting fuel causes the voltage to constantly cross above/below .450 volts.
e)If the voltage is latched below .450 volts (lean) a Code 51 (lean exhaust indication) may set in memory.
f)If the voltage is latched above .450 volts (rich) a Code 52 (rich exhaust indication) may set in memory.
g)To view O2 Sensor voltage/switching you need to tap into the O2 Sensor Signal Line using a Digital Multi-Meter, then you can watch O2 voltage to see if you are rich or lean.
h)The O2 signal wire is BK/DG (Black/Dark Green) on the "Harness Side".
(Do not confuse this with the DG/BK (Dark Green/Black) wire, this is a 12 volt power circuit for the O2 heater circuit)
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #5 ·
Thanks for your response.

I just took a look at error codes, right after my speed gauge decided to stop working (looks like a curse).
The three codes I got seems to make sense : 12 15 and 55.
So the speed sensor seems dead as after a reconnection i still have no speed gauge.
Do you think this can be related?
If not I'll take your list and proceed to all the checks.

Thanks a lot for your help!
 

·
Administrator
Joined
·
26,073 Posts
Repair the Code 15 first and then go from there, check the connector/terminals for corrosion/loose fit, etc.
The Mopar # for the VSS (Vehicle Speed Sensor, aka, Distance Sensor) is 5227897.
This sensor is all electronic, no cable which I assume is correct for this car.
The sensor is available in the aftermarket.

Here are Chryslers Diagnostics for Code 15 should you be able to gain access to an OBD1 scanner.
(DRBII, OTC Monitor 4000e, Snap On MT 2500)
Rectangle Font Parallel Symmetry Pattern
Font Rectangle Parallel Art Pattern


If not, here is the Principal and Theory of operation of the VSS and some diagnostic help.
Font Parallel Paper product Paper Document
Font Material property Parallel Rectangle Number
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #8 ·
Hi Folks,

I had the time to check the speed sensor.
No wonder it stopped working as the plastic gear was badly damaged.
Hand Wood Gesture Thumb Art

I replaced it with a spare one, and the backfires reduced a lot, so I think that was part of the issue.
Sadly, after a few miles, the speed reading stopped working again.
I think there's something in the differential, or maybe the passenger side shaft has a problem (which would be strange as it is brand new).
That's all for now.
Thanks again for the tips.
 

·
Administrator
Joined
·
26,073 Posts
There were 6 different vehicle speed sensor pinion gears used in 92 for an Automatic trans and 5 for the Manual trans.
Font Rectangle Parallel Slope Pattern
Map Font Rectangle Pattern Parallel

Other than the speedometer/odometer not being accurate I do not know if these gears are interchangeable.
With damage occurring to the Nylon Pinion Gear on your VSS rather quickly my assumption would be that you have the wrong gear(s) or there is damage or a broken piece of gear stuck in the output/intermediate shaft gear.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #10 ·
Quick update, i'll soon check what's wrong with the speed sensor.
I've 3D printed some pinion gears in PLA and PETG. If you're interested (and if it works) I can make some more.
 

Attachments

·
Legendary Driver
Joined
·
11,015 Posts
Jan, looking at your images you posted I see 4 gears for each trans. They correlate to tire size. Yellow, blue, and white in 19,20,21 tooth sizes for the non European models and an 18 tooth for European models, color not shown.

There were 6 different vehicle speed sensor pinion gears used in 92 for an Automatic trans and 5 for the Manual trans.
View attachment 280129 View attachment 280130
Other than the speedometer/odometer not being accurate I do not know if these gears are interchangeable.
With damage occurring to the Nylon Pinion Gear on your VSS rather quickly my assumption would be that you have the wrong gear(s) or there is damage or a broken piece of gear stuck in the output/intermediate shaft gear.
 

·
Legendary Driver
Joined
·
11,015 Posts
Fixing the speed sensor issue should help your deceleration running issues. When they go bad the car likes to shut off when cooking to a stop. Looking at the gear with the damaged teeth I would believe that the sensor stopped turning and damaged the teeth out maybe you damaged them when putting the axle in since you said the axles were new.
 

·
Registered
Joined
·
3,258 Posts
Also, there's a hidden screw on the throttle body you're not supposed to touch.

It works on the throttle plate just like the idle speed screw on a carburetor.

I find turning the screw to open the throttle blade a bit helps with decel backfires.

Actually, I like to adjust it so the idle speed never drops below my desired idle.

Thanks
Randy

.
 
1 - 13 of 13 Posts
Top