very slow hymer 410d om602 - PeachParts Mercedes-Benz Forum

wub · #1 09-04-2013, 05:09 AM

I have a 1990 Hymer on a merc 410 chassis, 2.9 om602.
It’s a large Hymer conversion, 660s, 6 berth and I also tow a small car.

The engine has been turbo intercooled, by JB intercoolers a few years ago, by another owner. Engine has done about 100k miles and is a good runner, starts first time, no smoke etc. My problem is lake of power. On a recent holiday to Italy, I had to drive it flat out all the time to keep up to 50 to 60mph, which rapidly dropped off to 25 to 40 on slight inclines. I also notice a huge change in power with different weather conditions (I think high and low whether pressure can affect diesel engines, but I didn’t realise to the extent it does, about 20 mph!) I have tried all sorts, fuel filters, checked for blockages, been back to the turbo garage, who checked waste gate etc. It seems from what I gather on the net that this engine in NA form is 95bhp and obviously higher with the turbo. But also on the web, it seems that the om602 in other variations ranges from 125 to 300 plus bhp tuned?

My question is, is this normal speeds to be getting from this engine? If so, is there any way I can substantially improve this? Tuning or complete engine swap for something else that will drop in without too much modification? I love the Hymer and don’t mind spending some on the engine to speed it up rather than buying another camper.

I want to be able to cruise at 60 without being flat out all the time, and for it to maintain most of that speed on moderate motorway inclines. I was often in 2nd or 3rd gear on the motorway in France and I’m not talking about going over the Alpes, just normal flattish roads.

I can’t seem to get to bottom of weather this engine is under powered or not. As its getting on a bit, nobody seems able to tell me. I get conflicting options from other owners, some say the 2.9 engine in these merc Hymers is fine, others say it is very slow. I guess I need to stick it on a rolling road to see what BHP it’s chucking out, anybody know of one in the West Country that will take a truck?

Unless anyone comes up with something amazing, I’m kinda fed up with it now, and am swaying towards an engine swap with something reliable ,but much more powerful /torky.

Does anybody have any experience with what will fit/bolt in without chopping bodywork around? Or can the existing om602 be rebuild/rebored, larger turbo/intercooler etc. etc. to produce a meaningful increase? Or better still, does anybody know who specializes in tuning these engines, preferably in the UK, but not essential?

I am determined to sort something out ready for next summer, I’m fed up with trying to overtake artic lorry’s doing 56mph, on the motorways, getting halfway past, hitting the tiniest of inclines, and then slowly dropping back, with my foot to the floor!

Any help advice, much appreciated.

John

Stretch · #2 09-04-2013, 06:04 AM

Hi John,

There aren't many people on this forum who have much South West England local knowledge about who would have a large enough rolling road. There's a guy in South Wales who pops by once in a while - user name Alastair - may be a private message / email to him will help?

But whilst most of here don't have the local knowledge you seek there are loads of people here who can help you check other stuff.

Assuming your rolling road idea doesn't come off - how about giving us a bit more information to help?

I'll start by asking

1) How heavy is your camper?
2) Which gear box / differential do you have? (Final drive ratio is useful)
3) Have you done a compression test?
4) Have you measured the turbo boost?
5) Do you feel that perhaps there's a fuel problem?
6) When your engine was converted to have a turbo did they re-tune the injector pump? (You need more fuel when you stuff in more air - just banging a turbo on the engine doesn't give you more power)

Stretch · #3 09-04-2013, 06:05 AM

@Super Moderator can we have this chucked over on to DD please? (Diesel discussion)

wub · #4 09-05-2013, 04:23 AM

Hi
Answers that i know.
1) Don't know, but its the largest model Hymer did at the time, so 2 to 3 meter over hang from back axle, scooter rack top boxes on and on. I'd say its at least max weight and probably more!
2) I put in the 711 113 manual box, to stop the engine screaming at 50 mph. I believe there were 2 manual boxes, the one i have and the 711 110, (the one i took out) which have lower ratio's, reducing top speed by about 12 to 15%, from previous research.
3) Have not done compression test, but engine is genuine 100K miles, was 75K miles when i bought it and have been told by various garages that its runs sweet as a nut, no smoke, rattles etc, good oil pressure etc.
4) not measured turbo boost, don't know how to do that?
5) Fuel, yes, i could write 4 pages on this! First thing i did was change the fuel filter on top of tank, then i was told there was another screw cartridge type on the engine, so changed that. Then told there was also a gauze in tank, took that out and it was clogged, so on advice, took it off and threw it away, letting the filter on top of tank do that job, as its a tank off job to get at tank filter.

I do have a problem with the tank as i have taken it off and cleaned it 3 times, but it still seems to clog up filters, so i am thinking its rusting inside and am in the process of looking into getting a stainless one made. I have a friend whole fabricates in stainless and could copy the old one. But i don't think it can be filters as i now change them all the time, due to the tank and trying to sort the problem, and i don't notice any difference?
I have also removed the throttle damper, (again on advice) the throttle stop under the peddle and checked the linkage to ensure pump is fully open under full peddle down.

I havn't changed the fuel pipes.
5) Turbo conversion was done by previous owner, but the company, J B turbo's was a respected professional company doing these conversions, so is a proper job. Has intercooler, pump was retuned and has been checked, waste gate all working etc. I havn't done any checks on turbo it self, but i can here it wine etc.

So that's where i am. I have to admit i have always thought it must be some sort of blockage, as I've been around engines all my life and dont think it's a nackered worn out lump that's the problem and others have said how good these are with the turbo conversion. I cant work out if its just different opinons on whats good or not, or if i have a problem?

On a camper forum, i talked to an owner of an exact same vehicle, model, age,engine gearbox with the exact same turbo conversion from same company, towing a car all around Europe, and he raved about how good it was, not a hotrod, but plenty of power for a camper. The only difference, they were a retired couple and i have a 4 kids, so a bit more weight to carry, but surly not enough to make that much difference? I even took all the intercooler pipes and intercooler off and air clearer off to check there wasn't a blockage there etc.

Its one of those things. I'm convinced there is a simple problem, given the guy above's opinions, but I have now had 3 garages look at it, spent hours myself and running out of things to try! The problem is, when stationary, all seems fine, its starts on the button, revs up fine, no hicups etc. Its when you are on the motorway, towing, fully loaded under full throttle with the wind resistant etc, that the underpowered feeling is there, which even as i write this, keeps bringing me back to fuel starvation or a blockage in the airflow? So under max load, when max air and fuel is needed, its not getting enough, but is getting enough on B roads etc where it feels fine. Again as I'm writing this, I'm coming back to fuel, as the only other time i feel under powered, is up a steep hills, again under full throttle, which is when power seems to tail off, and i end up in 2nd.

Surly there cant be any more than 3 fuel filters, ? Anything in the pump? So to recap, in tank gauze filter (removed), paper filter on top of tank, and screw cartridge on front of the engine.

Sorry for long reply, but you can see my problems, running out of things to try? New injectors, injectors blocked? But surly that would show on lower revs?

Thanks

Stretch · #5 09-05-2013, 11:42 AM

I reckon you need to start going through things in a systematic order. With the greatest of respect it sounds like you're now running about chasing your tail a bit.

Why not make up a new fuel tank (jerry can) and strap it to the front seat (or where ever) and run the engine for a bit with that. Follow the fuel lines - just get plastic fuel lines from a motor factors (Halfords even?) - and make sure that any fuel filters between the tank and the engine are changed. See how it performs.

If you start getting muck coming back down the return line - then that gives you a clue

If you have a sudden improvement in performance - then that gives you a clue

If you don't - well guess what? It isn't the fuel tank then!

Stretch · #6 09-05-2013, 11:46 AM

Oh I'm going to ask the moderators to move this thread to the diesel discussion.

You'll get more help from folks there =>

Diesel Discussion - PeachParts Mercedes ShopForum

bricktron · #7 09-05-2013, 04:17 PM

does this engine have an ALDA device? if so, there is a cleaning step and an adjusting step that could help. this will probably go hand in hand with measuring the boost since the gauge is usually spliced into that same pressure line.

gpb · #8 05-22-2014, 06:42 AM

Hi, an old post I know, but did you replace the small inline fuel filter which is clipped onto the side of the diesel pump, it's just a pre-lift pump filter but will cause the same problems you have if blocked..