Engine surge
 

I previously submitted a post regarding the engine surging on my '95 E320. the computer gave codes 2 and 3, so I replaced the O2 sensor, and while this seems to have helped a little, it has not solved the problem. The check engine light has not come on again over the last three days, but there is still some surging, albeit slightly less than the dropping to 500 RPM and surging to 1500 RPM. it's not too noticable while driving, although I can feel some hesitation and surging. mostly noticable when I come to a stop, when I pull my foot off the gas, it will drop to around 500 RPM and surge up to 1000 or so. pop it in neutral and it will do this drop and surge a couple of times then settle in at around 700 RPM, but the idle is a little shakey. I thought maybe EGR valve due to the shakyness, but the surge sounds more like mass air meter or throttle body issues. Can problems with the injectors cause this issue? can the throttle body be cleaned out? or is it a replacement item?

Thanks!

Gwet the codes from the HFM module [ Pin #8]

where can I get a code reader? I s'pose I could take it to a shop and have them pull the codes.

I found that, I'll go ahead and build one, seems easy enough, what gauge wire do you use? Once the check engine light comes back on, I'll see what I can find out.

any thoughts though on what might be causing these symptoms?

Yeah, I can come up with about a hundred...get the codes and we will probably come up with 2 or 3.

You do not wait for a CE lamp..CE is ONLY for the buit-in led emmissions module...that is why we want you to go to the real modules.

What gauge wire works best for this, 18?

I'll go ahead and build the reader and get back to you. thanks!

any light stranded..a led draws milliamps...

do you recommend soldering the connections?

Oh Boy ....


..yeah..solder, I like solder, yeah...

Ok, I built the code reader and here's what I came up with.

In position 8 - codes 13 and 45 (45 showed up this morning when I rechecked and didn't indicate last night)

In position 14 - code 11

I did replace the O2 sensor last weekend and the engine wiring harness is new.

Any help would be greatly appreciated

cheers!

Erase the codes, reset the memory and watch for new codes.
Suspect is sticking throttle cable..check that there is a little slack at adjuster end.

Erase the codes, reset the memory and watch for new codes.
Suspect is sticking throttle cable..check that there is a little slack at adjuster end.

Ok, I can fix anything on my landcruiser, but the benz is not something I have tinkered much with.

how do I erase and reset the memory?

where might I find the adjuster end of the throttle cable?

thanks

Easiest way is to use the Search feature...all that info is in the archieves.

pages upon pages on code erase, etc...

Curious, would a sticking throttle cable cause this back and forth surging or "hunting" as I've seen it called? Also, the code I pulled from position 14, is this relevant? and what exactly does this code mean?

Ok, I cleared the codes and rechecked later, got code 13 in position 8, again. As I said before, O2 sensor has been replaced, engine harness as well. engine was running rough at stops, and when I put my foot on the gas, there would be some hesitation and then some surging, in neutral, tach would drop to 500 then up to 1500 twice then settle in around 700, but still a little rough. exhaust smells rich. cruise control works fine.

I don't know exactly what you're referring to when you talk about the slack in the throttle cable...is this at the gas pedal or at the throttle body, and what exactly am I looking for?

What are some other common reasons for this to occur? I have a laundry list of potentialities, wondering if some are more probably than others; MAF, OVP, throttle actuator (bad wiring, gunked up), fuel pressure relay, coolant temp sensor, vacuum leak, bad injectors, etc etc.

Thanks, I appreciate all the input.

The cable is under the hood and it has a an adjuster wheel..that cable has to have 1/4" slack at idle position...and it has to move freely.

On the pin 8 code, you want to try a few easy test.
First one it to take the vac hose off the fuel pressure regulator and look for any evidence of fuel/vapors..that would cause the rich mix and throw a code. Again , " fuel pressue regulator" in achives..tells all about it in detail
Second is to look for vac leaks everywhere....

Ok, I'll check those things out this weekend. thanks again

Very good..

I only mention FP reg b/c they are known fault on this chassis and I see many owners change all kinds of electronic controls [and spen hundreds of $$$$$$$$$] in vain, when the first place they should have checked was FP Reg....
If reg is allowing raw gas into engine through the vac hose. all the ECU controls are wasting there time trying to correct b/c they can't control a leaking FP reg. They try to, but they can't............same goes for a big vac leak...ECU mangaement only has so much electronic correction/adaptation percentage capability..
So, check these FIRST...they may/may not be the problem, but they cost Zero to check.

So, I checked out the throttle linkage, that was fine, found the fuel pressure regulator and bingo! vacuum hose had somehow come off. Runs great now. Thanks for all the insight and prob. solving tips.

cheers!

Very Good.............

well, I may have spoken too soon on this one. Car ran fine for a couple of days and now is beginning to do this again. computer indicated the same code; 13 on pin 8. Doesn't seem to be as bad as before though. I haven't had a chance to check for fuel in the vaccum hose on the FPR yet, I'll check that. would a failing FPR push the vacuum hose off? Just curious since the hose was off the last time I checked. Going to Mexico on Friday, will play with it when I get back.

Cheers

The hose ends get loose from age, but you can cut them back a couple of inches and then you will see the inside diameter is smaller than the end was , so they will stay on again...this is a good thing to do to all older vac lines that have enough slack to allow the shortening of the hose...tightens them right back to new and eliminates many small vac leaks w/o having to repalce all the hoses.

A good test for your reg is to take the hose off and start the car while having a rag to catch any gas..if the reg is leaking by, it will dump out the vac hose port. Even a very small amount will fail the test b/c once a small leak has the vac hose back on, the leak becomes a large one b/c the vac sucks on one side of the diaphragm while you have fuel pump pressure on the other side.. ...not good, as all that gas winds up you know where............

alright, good tips. I'll try that out. thanks again!

Curious, how would this problem affect emissions? I suspect if it's running rich it may fail a portion of the test. Any thoughts?

Ok, I took the car to emissions just to see what the numbers looked like. This time around, HC was 10 and CO was 0. exactly two years ago HC was 93 and CO was 0.46. does the significant reduction in NC mean the car is running lean? there was no surging while at the station, but it surged the whole way home. any thoughts on how these numbers might relate to a specific issue? I still have yet to check on the FPR thoroughly.