Need help! 1988 190E won't rev up, seems to run very lean - PeachParts Mercedes-Benz Forum

lombrozo · #1 07-26-2013, 05:20 PM

Working on and off for years on this 1988 190E 2.3, trying to get it running well enough for a first car for a 16 year old girl - who is now 18!
Indy mechanic did all he could, replaced fuel pump regulator, and full electrical tuneup.
The car starts great and idles OK, and runs OK at light throttle, but as soon as the vacuum drops, it just falls flat. Put it in second and floor it, it just can't rev past 4000. I am guessing it is a fuel supply problem, filter is brand new and tank is full.
I do have a pressure gauge left over from my 1978 280SE. How can I check the pressures on this car?
What else can I look for? Clogged injectors? I keep hoping running some injector cleaner through will help.
Are there fuel filters other than the canister under the car?
I'll take any advice I can get, I am at wit's end and running out of time.
Thanks!
David

JamesDean · #2 07-26-2013, 10:43 PM

Somewhere I have this CIS fuel pressure test kit....IIRC, there is a test port on the fuel distributor. You would connect one line up to the test port and the other line to the cold start injector line.. I believe and this would give you system pressure and upper chamber or lower chamber pressure...and you were supposed to see a certain difference between them..I dont recall 100%

http://www.startekinfo.com/StarTek/outside/11832/?requestedDocId=11832

See this PDF:
http://www.startekinfo.com/StarTek/outside/11832/Resources/201Create/PDF/30006.pdf

Service Manuals
Mercedes Factory Service Manuals

lombrozo · #3 08-08-2013, 02:26 AM

1988 190E, that has been pretty much off the road for 4 years while I have worked on and off on it.

So here is the symptom:
starts instantly, idles OK. Off idle throttle response not as strong as it used to be. Looses power when the throttle is opened. When the economy gauge drops to halfway, it bogs. Will not rev past 4000.

New plugs, wires, cap, rotor, fuel filter, air filter.
Ran the fuel pressure test with the proper gauge, 5.5 Bar system pressure. 4.9 bar lower section pressure.

Thought it might be a clogged tail pipe, I opened up the exhaust and made it into a clean through pipe, and left the rear section disconnected after the resonator.

I disconnected the O2 sensor (I am replacing it tomorrow) but thought that is an interesting test, it would be all mechanical rather than listening to the sensor. Still ran the same.

Tomorrow I will try the LED box and duty cycle test. I am not clear on which connector to put the LED box in - this is a 1988 190E 2.3 4 cylinder, automatic. Is the plug on the passenger side by the battery or on the driver side mid fender?

Is it meaningful to look at the duty cycle when I don't have the O2 sensor connected? Or am I better off installing it and hoping for a shot at a good setting?

I am thinking about clogged fuel injectors. I once made a pressure test rig using the air compressor, for a 1978 280SE, I could try to recreate that. If it is a clog I am looking for, and not dribbles and leaks, would it be valid to pull one injector at a time, reconnect to its fuel line, disconnect the spark plugs, and crank the engine to see what the spray pattern looks like?

Or same setup, but start the engine on three cylinders to get a more realistic test than a cranking test?

A lot of wit's end here, I have to get this thing finished and this poor running is the only thing keeping it off the road.

All ideas welcome!

David

JamesDean · #4 08-08-2013, 08:33 AM

A good next step would be to get a multi-meter and probe the x11 port (driver's fender) and see what the duty cycle is at. I believe you want pin 3 = + probe, pin 2 = - probe.

Ideally it should be fluctuating 40-50% after 1-2 minutes at idle. This is normal operation.

IF you see a fixed value, like its stuck at 29.9% or 30% (or some other percentage) and does not move at all when you give the car throttle... Then you have a faulty component. The CIS book will tell you what to check for. I think thats in the above pdf. If not let me know.

If you see it fluctuating at like 70-80% or 10-20% then you need to adjust the lambda tower and get it back to 40-50% duty cycle.

This car wouldn't happen to have ASR would it?

Hope this helps!

lombrozo · #5 08-08-2013, 04:03 PM

I bought a cheap DVM just to get the duty cycle feature - I already have a dozen free-with-coupon Harbor Freight DVMs scattered around.

I don't have ASR.

I believe I need the LED box, which I built a while ago, to go into diagnostic mode. I may have misused that the last time I tried this measurement.

First, in with the new O2 sensor. I'll keep you posted.

JamesDean · #6 08-08-2013, 04:11 PM

Thats what everyone told me too but I've never had to do it.

I just connected up my meter to the X11 and read out the duty cycle.

Let me know what you come back with.

If you've got a bad Oxygen sensor it will read out a solid 50% after you let the engine sit for abit.

IIRC, the engine start out in pure mechanical mode, which will read out 50%, then it will go to computer control, closed loop, and start adjusting which is where the duty cycle should start to change. If it stays constant at X% then you've got a faulty component somewhere.

lombrozo · #7 08-09-2013, 04:10 PM

Replaced the O2 sensor and hooked the muffler back up.
Found that the car DOES have a little button and an LED in the battery compartment. Before pressing button, X11 pin 3 read 12.5V

Instructions say press button for two seconds and it will flash once indicating no trouble codes (Check Engine Light is not on). Mine did not flash, went to steady on, brighter when button held than when release.

Was seeing key on - engine not running steady state voltage of 6.6V - so about 50%. Not clear what that means.

Started car and let the O2 sensor warm up for a minute. Saw the duty cycle moving around, between 55% and 34%, roughly. Gave the tiniest twist counterclockwise to the lambda allen screw, brought it closer to averaging 50%.

Revved the car up to about 3500, saw it seem to be more clustered around 50%. Tried to rev it higher, before it would not exceed 4K in neutral. It sort of hung and that point, then broke through and revved up to redline!

I suspect I might have blown out a clogged injector?

Took it for an aggressive test drive. Not perfect, but running better than before. I have a feeling that putting some miles on it will clean out the injectors. Or at least a hope.

It will rev up past 4000, but it is not making much power, I would expect to get pushed into the seat, but really it is watching the needle slowly climb in 3rd gear.

Any suggestions on the next thing to check? I suppose I should replace the injectors, but am holding off on that.

JamesDean · #8 08-09-2013, 04:14 PM

Throw a bottle of Techron in the tank and go for a drive. The 2.3 8 valve is not the most powerful thing out there. I think 0-60 times are in 10-13 seconds? Maybe?

lombrozo · #9 08-14-2013, 04:57 PM

20 oz bottle of Techron, and ran a tank through it. The car has two modes, it idles/runs lumpy and won't take the throttle - anything more than halfway on the Economy vacuum gauge and power is reduced - you lift off the pedal and the car speeds up.
It won't rev past 4000. Then it goes randomly into a mode where it clears up and will run to redline.
The idle is higher than it should be and vacuum too low at idle.

I have convinced myself that the fuel injectors must be clogged and at the spray pattern is sub-optimal even when they are flowing. I think the IAC is holding the idle high for me and causing the reduced vacuum.

I have ordered a set of injectors - only $75 with postage from ebay, and some seals. Next week we will know more.

lombrozo · #10 08-22-2013, 06:05 PM

I installed the new injectors, the car started up grossly rich - good sign, moving more fuel through the new squirters.
But I can't get it to go into diagnostic mode. I pressed the little button by the LED near the battery, light does not go on. I don't see a voltage or a duty cycle on pin 3 of the round test socket.

Last time, the light went on steady on the first 2 second push, rather than flashing as I was expecting, but I was able to set the duty cycle.

I pulled the battery overnight hoping to reset everything.

I guestimated the tower adjustment and leaned it out quite a bit and it is running much better. Idle is way too high, 1200+ in N, 700 but lumpy in D.
Just off-idle rolling on the power, it is lumpy and in gravel wants to spin the tires. Once underway, it pulls smoothly but not terribly powerfully.

I never drove one of these that worked well, so I don't know what to expect. Going to full throttle, even above 4000, does not have much effect vs half throttle. Really hoping to get diag mode running and convincing myself it is as good as it will get.