Intermittent loss of power

Fiero1441 · **Intermittent loss of power -** 11-11-2008, 06:35 PM

Hi, My 1991 190e 2.6 has power problems. It takes a really long time on the highway to get to highway speeds. Once at 60, I can get it no further. And I slow down going up hills. If I have to stop at a light, I have a very difficult time getting it moving again. When I am driving, at any speed, there is a very narrow range I have to keep the pedal in. If I press down too fast or too far for the speed I'm at, the car starts to stumble and it sounds like it is backfiring into the air cleaner. But only if I press the pedal as if under hard acceleration. If I very gently press the pedal and take 10 mins to get up to 60, there's no backfiring. Nor is there any backfiring when cruising at 60 on a flat highway.

So far, I've verified that I'm getting spark to all cylinders. New plugs (non-resistor) and new wires. New fuel tank strainer, new fuel pumps, new fuel injectors, new O2 sensor. I've replaced the fuel distributor/EHA valve, the fuel pressure regulator, and the OVP relay with parts from a salvage yard. I've cleaned the IAC valve and it is operating within spec. I've measured the fuel flow and it seems fine. I do not have the equipment to verify pressure. I cannot get a duty cycle on X11/2. I get a voltage reading that is initially the battery reading and it slowly and steadily drops to zero. As I changed parts (whether new of used), the performance increased ever so slightly but nothing has fixed the problem nor have I been succesful at diagnosing this. Not being able to get a duty cycle reading, I've adjusted the lambda tower by ear. I've tried setting it at both extremes of CW and CCW where the car still idles acceptably (making it richer and leaner). No apparent difference. The car has no problem starting either hot or cold.

Most cars also seem to run better in humid air (better burn rate, I guess). This one runs much worse in high humidity but its not arcing the spark. It also seems to run better when it's cold outside. I've also cleaned the mass air flow sensor. I've also done some checking for vacuum leaks but so far haven't found any. The throttle body seems to be sealed fine.

Anyone have any ideas?

Wolf190 · 11-11-2008, 07:15 PM

You didn't say anything about the air filter... It is best to start with the basics. Check for a clogged filter.

Also a clogged catalytic converter could cause problems, but I don't see it having the effects that you are describing.

At work when we have a car acting up we sometimes start by removing all electrical connectors (one at a time) and spray them with either electrical contact cleaner or a di-electric grease/cleaner.

Did you check for vacuum leaks?

So there's a few. Don't mean to insult your intelligence or anything but these are the rules I've learned to live by with these cars. Easy stuff is what usually goes wrong.

ghosts · 11-11-2008, 07:46 PM

Air filter, fuel filter, clogged cat, blown coil...

I had a 1980 Chev Silverado that had a bad habit of clogging fuel filters... clogged up so bad I couldn't get it past 80 km/h... and if I romped on the throttle, it'd just stall out. :\

Fiero1441 · 11-11-2008, 07:51 PM

Air filter is new, fuel filter was replaced when the pumps were replaced. I even tried testing without the air filter altogether. I also tried running with the exhaust disconnected at the manifold. Other than being loud, it made no difference. Spark seem strong so I doubt the coil. I did some checking for vacuum leaks but probably didn't get all the lines. Didn't find any obvious leaks.

TiE10 · 11-13-2008, 01:28 AM

and its definitely not head gasket?

dan_189 · 11-13-2008, 07:50 AM

I had the same thing today, its hot 34 degrees and the car was struggling really badly. Had 4 people in it but it usually does fine, the brakes were not performing their best either. Had the air con on for a while but I turned it off because it felt like walking would be faster than driving...