L400 diesel surge

DustAngel

DustAngel

Well-Known Member
While driving diesel van after warmed up, at times when I am at partial throttle around 1500-2000 rpm and in second to third gear on automatic transmission, I get a surge and the transmission seems to “hunt”. I have used a digital multimeter to watch the TPS values and I do not observe a flat spot. When I bought the van, I was told that the diesel injection pump had a seal replaced and timing optimized close to factory spec. Question... can the TPS still cause an issue like this? Also, the transmission shifts firm when all is going smooth. Anybody experience these symptoms and find a solution? Help is appreciated!
 
I get a bit of surging too, although mine's 5MT. It typically happens in 4th gear at about 2,800 RPM while accelerating. I'll be interested to see what you find.
 
Crankshaft Culture said:
I get a bit of surging too, although mine's 5MT. It typically happens in 4th gear at about 2,800 RPM while accelerating. I'll be interested to see what you find.
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Hopefully we both gain some shared insight, short of learning the injection pump, I have only started with tps ... I have read that tps wears out but in my experience there is usually a noticeable flat spot.
 
A slightly worn TPS can produce a signal that has spikes in it (like the crackle from the speakers on a worn volume knob) which are too short to show up on a multimeter, but which confuse the transmission ECU. You'd need an oscilloscope to see the real quality of the signal, but the TPS is a common failure point so it might be worth just replacing it.
 
I will scope the tps sensor and see what I find. Not a bad idea to replace as I plan on keeping the van. Could a speed sensor cause this? Ok, I found how to flash the ecu for codes and there aren’t any present. Wondering if tps sensor could be bad according to growlerbearnz suggestion without code present.
 
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Ok, put scope on the tps sensor. Clean pattern up and down, in and out. What I noticed is the sensor position originally as I had received was at .78v on DVMeter, in center of adjustment. When using the scope, I noticed that it said 1.22v for low value. Hmmm. I adjusted the sensor all the way to one side, or really close to approx .87v low value, 3.87v high value and went for a test drive. No surges through any gear, AC on or off, and pwr setting on dash for transmission works well too. I notice that the van shifts smooth but it seems to run well. When I had bought the van I was told that injection pump will be “optimized”, whatever that means...this would have been done at sea level. I live at 5000ft above sea level and see anything from 10k to sea level on my journeys. I do believe there is altitude sensor but I am still learning. I will drive tomorrow and see if there is anything that comes back. Any suggestions are always appreciated!
 
I have been driving the van today and it is much better. I still have an occasional surge under near wide open throttle but it’s not near as bad as it was. I ordered a new tps and will adjust it accordingly when I receive.
 
Progress! Woo!

Google "L400 TPS adjustment" (If you haven't already). From memory most people find it drives best when it's set to 0.78V at idle? Or something like that... Others add a variable resistor in series, to bring the overall voltage down.
 
Progress for sure although I agree to find the .78v optimal on the interwebs. My current setting has a small surge leaving the intersection and it smokes a lot more during moderate/light acceleration. I split the difference on original and what I did last night and now I am at .78v... weird right? I compared three meters and two sets of test leads. Seems that after locking down adjustment one must operate the pedal a few times and recheck. Driving now, will update again.
 
Driving is now less smoke but I still have WOT surge, if I tune that out, I get heavy mid throttle smoke and an occasional crackle that sounds like a Ford 6 liter diesel. I am going to leave alone until new tps arrives. I am not confident that the tps is the issue given the pattern on scope. Hard to imagine that these vans ran like this off of the showroom floor. Wonder what else could be culprit? I have purchased fuel from different stations over this month, I have used some lubricity additive but none for three tanks. I don’t see fuel to be the issue... any other sensor play into this? Once again, no codes in trans control module
 
Honestly this could be a transmission or torque converter issue at this point. How much boost are you running?
 
@Kellyn Stock boost to my knowledge until I install gauge to verify. I checked the kickdown and throttle cables today and cleaned as many grounds as possible. I did notice that the body ground with factory crimp by batteries was 29 ohms so that is now 0. Drove van tonight with ac on and off, power and normal shift points for auto transmission. All drove well without issues, for now! Transmission shifts good and I don’t see where the valve body solenoids or torque converter are acting up. I still notice that the tps voltage is back to 1.18v-4.24v without changing adjustment from yesterday’s values of .78v-4.04v. I still await the new tps to install
 
Fingers crossed for a bad chassis ground being the cause? I haven't heard of a bad earth causing trouble for years. Bad earths were all the rage on '60s and '70s British cars, pretty much any time something went wrong you could cure it by putting a jumper lead between the battery and engine block.

Oh god. I just realised: I'm really old.
 
Growlerbearnz said:
Fingers crossed for a bad chassis ground being the cause? I haven't heard of a bad earth causing trouble for years. Bad earths were all the rage on '60s and '70s British cars, pretty much any time something went wrong you could cure it by putting a jumper lead between the battery and engine block.

Oh god. I just realised: I'm really old.
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Hahaha!

2nd this! I hope this sorted your issue! I have an auto l400 and I'm watching your issue closely.
 
Today I drove the van 300ish km. and noticed very little surge. Once again I tried with and without ac and different speeds, hills, and other situations to make it surge. The van ran great although I noticed some uphill WOT had light surge. I think cleaning grounds always helps, but as @Growlerbearnz states, that was more of a fix for older cars. Something did get better for the drive today. Next I will do nothing and drive it tomorrow to compare. I plan on replacing tps because it seems like it just doesn’t hold calibration to that magic .78v
 
Ok, I have now tried a new tps sensor. I have been using an oscilloscope with voltage setting to calibrate, and I have double checked with another fluke meter and voltages are accurate. I have tried .78, .85, .98, 1.1, 1.2 volts to see what works best. I have set these values at normal operating temperature, AC off, and good voltage on batteries. I have random surging at different times . Tps is smooth shifting at lower values and slightly harder shifting at higher values. Kickdown cable is adjusted and working properly and torque converter locks at the correct times to my knowledge. Egr valve is hooked up, although surging was present with it disconnected when I purchased the van. Sometimes at light throttle and low speed I can hear a quick fuel knock sound similar to the cackle of a Ford 7.3 diesel. I guess this is an intermittent poor fuel delivery condition? Before I start going into the tangent of the injection pump and it’s operation, does anyone have any insight on this surge? Any fuel pump, line, or filter conditions to look for? Fuel filter is new.. help? Thanks!
Ps, I have tried different quality diesel fuels with and without additives FYI. Last 5 tanks with no additive.
 
Ok, so I finally got the injection pump fully reconditioned by zexel diesel shop. Install was easy and van no longer leaks diesel fuel. I still have a surge when accelerating and I am wondering if injectors could cause this? Egr valve is removed and timing marks are oem to my understanding. I would imagine that diesel shop would have calibrated the pump.
 
Yes the diesel shop would have calibrated the pump. A surge is almost impossible to see on the calibration stand. We have to remember that there is no "dynamic" reaction on the test stand. Meaning, The operator is controlling the rpm of the stand and the throttle position individually . On the engine the throttle position and engine speed and load are constantly responding to each other.

Fuel supply can cause a surge. If there is small amounts of air entering the pump. We can see that by tapping into the return side of the injection pump and see what is coming out of the pump. Any air getting into the pump will come out of the return.

Make sure there is no play in any of the linkages for the throttle.

I have not seen an injector cause a surge during acceleration. (I have been wrong before.) The fuel shop should be able to test the injectors pretty quick. As long as they do the injectors at that location. I thought you said they sent your pump to a different location.

The issue can be the nozzle availability. Our 4m40 injectors were never used in the states. Plus there are a couple of different nozzles that were used in the injectors. Zexel (AKA Japanese Bosch) had mine in Germany. So it was only 5 days (With no extra shipping.) So I ordered an 4 nozzles. (Have these and some for the L300) What ever you do, do not buy Chinese injectors. They are crap and will lead to more issues.

To rebuild these injectors should not really be more that $70ish each plus seals and gaskets. With factory Zexel nozzles.
 
Thanks for the guidance Scott! Injection shop sent to main location in Oakland California. Zexel parts were used and to my knowledge pump is as new as it gets! I have a set of rebuilt injectors from delica garage Australia. I will install them soon and report back. I used new oem fuel supply and return hoses when I reinstalled the injection pump.
 
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