“Rumble strip noise” on 2001-2006 Sprinters is a syndrome that results from an intermittent transmission NVH condition, caused by the Sprinter’s over-active torque converter clutch duty cycle program. In some coasting or deceleration situations, the converter’s duty-cycled lockup activity can set up a rhythmic vibration in the drivetrain, creating a booming resonance inside the van reminiscent of the sound created by driving over a rumble strip in the road. When it is severe, the noise can be a major irritation for drivers and passengers in the van, and it detracts from the otherwise smooth and refined Sprinter diesel powertrain. The Sprinter’s torque converter clutch operation is managed electronically by the TCM (trans control module). Under conditions that call for partial or complete torque converter lockup, the TCM sends duty-cycled pressure through the torque converter clutch control circuit and the TCC is applied as necessary. The problem in the Sprinter that causes the RSN symptom is that the TCM’s lockup strategy is overly aggressive, calling for partial converter lockup at inappropriate times and eliciting the rhythmic drivetrain harshness that passengers experience as RSN. The fix for this issue, as devised by Sprinter guru Doktor A, involves a modification to the TCC spool valve circuit in the transmission valve body. This is accomplished by creating an orifice of precise size in the valve body’s steel side cover plate at the exact location of the TCC spool valve, permitting a calculated amount of TCC circuit pressure to escape and thereby altering TCC lockup behavior in such a way as to eliminate the RSN syndrome. With the transmission sump lowered, the exposed steel cover plate on the driver’s side of the valve body can be carefully removed for modification. Caution must be exercised to make sure none of the springs or pistons that sit directly behind the plate are allowed to fall out. A helpful trick is to do this repair with the van jacked up on the floor, rather than on a shop hoist, and support it using adjustable jack stands. By using a taller jack stand on the driver’s side, the van can be tipped a few degrees over toward the passenger side during service, reducing the tendency of the valve body internal parts to fall out when the cover is removed.
Once the side cover plate is out, it is wiped clean and marked to determine the location for the drilled orifice. The plate has three screw holes at the front that form the apices of a right triangle. Using a straightedge, lines running parallel to the sides of the existing triangle are drawn to identify the location of an imaginary fourth hole. Next, two diagonal lines are drawn, running from the center of each hole to the center of its respective opposite and crossing at the center of the rectangle. The intersection point of the diagonal lines is the location where the TCC spool valve lives and where the orifice will be drilled. Using a micro drill bit, the orifice is created at the intersection point. A #55 drill size is appropriate for most vans, though according to Doktor A, a smaller #56 drill may be used to satisfactory effect in vans that have particularly mild RSN symptoms. I used a #55 on this van, which was suffering from severe RSN. When looking at the inward side of the cover plate after drilling the orifice, the witness mark left by the TCC spool valve sitting against the inside of the plate is faintly visible, with the new orifice centered within the spool valve’s circular mark. The new orifice should be carefully de-burred and the cover plate cleaned of any metal filings before reintroducing it to the transmission. It is a good idea to check once more that all the valve body springs are still present and in their correct positions. Finally, the modified side cover plate can be installed, taking care not to over-tighten the tiny screws. With the pan already dropped, this is also an easy opportunity for performing a complete trans fluid and filter service. On a Sprinter, it is possible to drain the torque converter as well as the transmission from underneath. First the rectangular rubber plugs in the bottom of the bellhousing must be removed, and then the crankshaft can be rotated from the front using a 27mm socket until the TC drain plug comes into view. Trans and torque converter buttoned up from underneath with a new filter: now time to add just under 8 liters of 236.14-spec ATF. Sprinters have a transmission fill tube under the hood, but no dipstick. The correct dipstick for measuring fluid level is a Mercedes special transmission service tool that must be obtained separately under MB P/N 140 589 15 21 00 and used in accordance with proper procedures. Once the fluid is topped up, the van is ready for a smooth, quiet, vibration-free test drive. Credit and thanks go to Andy Bittenbinder (abittenbinder a.k.a. “Doktor A” on the Sprinter Forum) for developing, testing, and providing information about this clever and effective repair. Doktor A sells an RSN fix kit that includes the necessary tools and complete instructions, and Sprinter transmission service kits w/ correct ATF, dipsticks, and other needed parts are available from sources online.
Note, in response to some questions, that this repair method is applicable only for pre-2007 Sprinters and is not recommended on the 2nd generation 2007+ V6 powered vans, where it may cause a transmission diagnostic fault and limp-home condition, that can be resolved only by reversing the repair procedure. It should not be attempted on 2007 or newer.
I WILL REPEAT ONCE AGAIN – THE REPAIR DESCRIBED ABOVE IS INTENDED ONLY FOR 2001-2006 T1N CHASSIS SPRINTER VANS USING THE 2.7L 5 CYLINDER CRD ENGINE, AND IS NOT RECOMMENDED FOR 2007-UP NCV3 VANS.
Note furthermore of course that the above repair description is provided as anecdotal information and does not constitute “instructions” or any kind of advice as to what YOU should do to YOUR vehicle! This is a description of one experience but yours could be different, it is published *free* on the INTERNET for general interest consumption, and is not intended as a repair guide. I accept no responsibility whatsoever for how you use the information, or any results you achieve.Thanks for your comments. George
T1N-platform Mercedes/Dodge/Freightliner Sprinters are susceptible to a couple of unusual issues as they age. One is an internal failure of the glow plug relay that results in a check engine light with code indicating a glow plug fault even when all plugs are good. The other is a syndrome known as “rumble strip noise,” which is an NVH phenomenon that manifests as a loud rhythmic booming that is audible inside the van in certain circumstances. Each can be permanently solved with effective and relatively simple modifications. I had a chance to work on a van that showed up with both problems, and took some pictures as I carried out the diagnosis and repairs.
Sprinter Glow Plug Relay Failure
Rather than a single external high-amp glow system fuse, as most diesels use, Sprinter vans feature a glow plug relay that has five small internal fusible links inside it. (In fact, there are not five but six fusible links in the relay, since this same part is also used for the six-cylinder variant of this modular engine as found in the MB E320 of similar vintage, but for the 2.7L Sprinter application only five of the links are used.) Each of the five individual glow plug circuits is monitored by the glow controller, and if a fault is found with one or more of the plugs, the controller reports the problem to the ECU which turns on the check engine light and sets a DTC (usually both a P0380 general glow circuit fault and a P067x individual-cylinder fault where x = 1 through 5, identifying the number of the cylinder with the failed plug).
If a plug fails open, replacing it and clearing the code is sufficient to restore proper function. However, if the plug fails shorted, it will blow the fusible link inside the GP relay for that cylinder, resulting in an open circuit that will remain even after the faulty glow plug is replaced. Consequently that new glow plug will receive no power and provide no preheating in the affected cylinder, and the relevant trouble codes will continue to set even without any externally traceable glow system faults.
The standard repair in this situation is to replace the glow plug relay. Unfortunately, list price can exceed $250 for the relay alone, less installation, so this is not a cheap repair. Worse still, if the system suffers another shorted glow plug in the future, the new relay will be damaged the same way the previous one was, and yet another replacement will be required. For most owners, repeatedly replacing expensive glow plug relays is not a practical option.
The alternative is to modify the original relay and relocate the glow plug fuses to an external location, where they can be easily replaced individually in the event of a glow plug short without affecting the relay itself. This is the only way to salvage a failed relay, and additionally it improves ease of service and dramatically reduces cumulative repair costs in the event of a future glow system short.
This van had a chronic check engine light with the typical glow plug failure codes stored; replacement of glow plugs had yielded no improvement, so it was a likely candidate for relay failure. Sprinters have the glow plug relay located on the driver’s inner fender, tucked up underneath the battery tray. Easiest access is obtained by removing the grille and LH headlight assembly. The battery should be disconnected before attempting to remove the glow plug relay, since the relay’s large B+ feed wire has a non-insulated terminal and requires tools to detach. (If your Sprinter has its original radio, at this point you will want to make sure you have your radio security code on hand.)
After removing the relay cover, the failure is easy to see. Evidence confirmed the hypothesis that this van had suffered a shorted glow plug sometime in the past, resulting in the burned internal fuse link that was causing ongoing problems.
The relay has two banks of fusible links, three on each side. The link running parallel to the right of each fuse link, connected at the bottom but leading to a different terminal at the top, is for the system’s diagnostic feedback; it allows the glow controller, integrated into the relay, to monitor the actual conditions in each glow circuit and determine whether that plug and circuit are functioning correctly. If the fusible link is blown, current will not make it down the left side of that link to reach the bottom, where the glow plug harness wires begin, and additionally no current will be fed back to the controller’s monitoring system through the right side link, signaling that that cylinder’s glow circuit has a problem.
The relay modification consists of soldering a large power feed wire onto the switched hot side of the relay itself, which then supplies power to the “in” terminal of an external fuse panel. The fuse panel is then set up with five individual, replaceable fuses, each with an “out” terminal feeding power through five separate wires back into the glow plug relay. The end of each of these wires is soldered to its respective glow relay “out” terminal, which the original fusible links would have fed power to (and which is still being monitored by the feedback link on the right hand side of each terminal, as designed).
The end result is that the entire system functions just as before, except that now in place of the internal fusible links are five standard external fuses, with associated wires added for powering the fuse panel and returning the fused power back to the relay. Any faults resulting from a shorted plug can now be remedied by simply replacing that plug and its corresponding fuse. No more expensive glow plug relay failures.
Sprinter RSN Repair
Heater core and blower motor replacement on a 1984 Volvo 244 Diesel.
Heater unit with new heater core and blower motor installed. This is also the right time to replace the blower motor resistor and test all the HVAC vacuum servos and diverter doors for proper function. When reassembling the heater case, it is easy to misalign the doors and their hinge pins, so care must be taken that everything fits together and works afterwards.
This was the kind of job where you look at it taken apart and wonder if it can ever be whole again. Yet, many tedious hours later…
How it turned out:
Car has been on the road and running great since repaired, doing almost 5000 miles to date in this customer’s hands.
What it took to get there:
- One weight- and length-matched replacement #4 piston-conrod assembly
- One new (rebuilt) cylinder head
- New head gasket, head bolts and head set
- One new injector tip and all 4 checked/serviced
- New rod bearings and 8 new TTY rod bolts
- 4 sets of new piston rings
- One new glow plug
- Complete deluxe timing belt kit
- New fuel filter
- About 13 hours of labor, and…
- About 4000 bucks.
Very fortunately, when the #4 exhaust valve broke off inside this engine, it was held mostly in place by the combustion chamber set into the top of the piston, and as a result the destruction was almost completely confined to the piston, connecting rod (bent), and head. Those parts suffered catastrophic damage, but the crank and bore escaped injury and the engine internals were otherwise in good condition, which meant that this motor was a candidate for in-situ repairs.
A replacement #4 piston + connecting rod assembly was obtained, matched in weight and length to #3, its reciprocating mate, and piston protrusion at TDC was checked in all 4 holes to ensure even compression and smooth running — and to verify that the other rods and crank were not damaged. This engine had suffered a broken timing belt at some point in its past, with piston-to-valve contact marks visible on the other piston crowns. Whoever repaired it at that time apparently installed a new belt without overhauling the head, leaving impact-weakened valvetrain components in place to fail later on and cause further destruction… which they did.
After giving the bores a quick hone, the engine was assembled, gaskets and fluids were tended to, and a complete timing belt service was performed. Finally, the key was turned and the Jetta awoke from its coma in a healthy haze of smoke and lifter clatter. Success!
This ALH motor was the victim of an avoidable disaster. With some intensive surgery and a bit of good luck, it survived with a new lease on life… but you don’t want to let this happen to you. VW diesel timing belts must be changed on time!
The leftover pile of FUBAR parts:
I did a camshaft and lifter replacement on a PD TDI last week. The PD engines have a characteristic tendency towards premature valvetrain wear, due to flaws in design and materials. At ~88k miles, this car was in the early stages of camshaft failure. This was a preemptive replacement of camshaft, lifters, and cam bearings with updated parts before the problem got bad enough to affect the car’s driveability or damage other engine components.
The patient: a 2004 Jetta Wagon, engine code BEW.
Mostly disassembled. Valvetrain must be taken apart one-half crank revolution *before* (or after) #1 TDC so that the tandem pump drive slot in the back of the cam is vertical, allowing the cam to be lifted out without removing the tandem pump.
Parts removed from engine.
Closer view. Not pictured is the cam, which had significant wear on the exhaust lobes of #2 and #4 cylinders, with corresponding wear patterns evident on the surfaces of those lifters. The lower cam bearings were also worn to a severe degree, as is characteristic of the PD design.
Head with new reversed lower cam bearing shells and updated black nitrided-finish lifters installed.
Cam bearing caps with modified upper bearing shells installed for improved oil flow.
New cam lubed for installation and set into place. The valve lobes on the PD cam are unusually skinny to make room for the wide injector lobes. The thin valve lobes and resulting high psi forces between the lobes and lifters are a main factor in the PD design’s problems with premature cam and lifter wear.
Cam torqued down w/new hardware, timing gear and belt installed, engine set back to TDC and timed.
Injector rockers installed and injector lash adjusted.
Cam torsion set, buttoned up and running smooth.
Welcome to my blog. This page will be a place to share pictures, experiences, and information collected in the course of my work that I think may be interesting or useful to others who share my interest in and connection to diesel engines and vehicles and alternative fuels. It is inspired by a handful of similarly-oriented technical blogs written by others that I have enjoyed reading over the years.
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