Car lays down if you get in it off a cold start.

[Ascension]

My 95 E 420 will come up in the revs then suddenly nose over then come back and does not have to be at close to full throttle. Only does it before it fully warms up after it's fully warm seems fine all the way to redline. Suspect a fuel issue of some kind. Mine is a late 95 so may have the single pump can some one decipher off my VIN as to which system I have? I have never heard a pump under the back seat on my car so--. Anybody got insight on this as seems strange it's only after it has sat a while and as soon as she is fully warm there is no issue.

 

[nocfn]

So in the morning cold start, it automatically gets about 10 on the RPM scale, then after 20-30 seconds it drops to 7.5 them about 5.5. You put it in gear and then you drive in low gear until the car heats up more then the sensor flips the gear to second (420) and then the car is fine? Sounds fine to me.... normal behavior. Not sure it is an issue, especially after temp rises off the peg things are normal.

 

[maw1124]

@nocfn I think he's trying to describe a flat spot in the power curve but I'm not sure. OP, please explain more clearly what you mean. Flat spots in the power curve are known issues (I forgot what it was on mine, but it happened in prior ownership). I want to say caps / rotors but I'm not sure. It wasn't pumps or LH module as those were handled under my ownership.

maw

EDIT… OP, this might be a good read… SOLVED: Uneven idle, hesitating when accelerating, power is down (Faulty CKP) | Troubleshooting and Diagnostics

 

[Ascension]

@nocfn I think he's trying to describe a flat spot in the power curve but I'm not sure. OP, please explain more clearly what you mean. Flat spots in the power curve are known issues (I forgot what it was on mine, but it happened in prior ownership). I want to say caps / rotors but I'm not sure. It wasn't pumps or LH module as those were handled under my ownership.

maw

EDIT… OP, this might be a good read… SOLVED: Uneven idle, hesitating when accelerating, power is down (Faulty CKP) | Troubleshooting and Diagnostics

Now that the weather is getting cooler problem is back. Car will start and run fin with absolutely no misfiring. Under brisk acceleration will suddenly just nose over then come back. Pull back on the throttle and it will catch and to me this feels like a fuel supply issue. Is much worse when the engine is cool and will just lay down at WOT. Was also much worse with the 92 LH in the car I have. I'm wondering if the fuel pump is going. Need to run the VIN as I suspect this car has the single pump being a late 95.

 

[maw1124]

That actually does sound like fuel delivery. Almost like it’s running lean under load. Put a gage on it, it can’t hide. Did you rule out crank position sensor?

maw

 

[JC220]

Sounds like the classic m119 ignition issues

Thread 'Essential M119 Ignition "Tune Up" mods' FYI - Essential M119 Ignition "Tune Up" mods | M119 Engine

 

[gsxr]

Now that the weather is getting cooler problem is back. Car will start and run fin with absolutely no misfiring. Under brisk acceleration will suddenly just nose over then come back. Pull back on the throttle and it will catch and to me this feels like a fuel supply issue. Is much worse when the engine is cool and will just lay down at WOT. Was also much worse with the 92 LH in the car I have.

When the power loss occurs, is it perfectly smooth, with zero misfiring? If so, this may be failing fuel pump(s). I've had this occur on at least two different cars. However the only way to prove it is the pumps, is to connect a fuel pressure gauge that can be viewed while driving. Pressure will drop drastically (say, down to 20psi instead of 50) when the power loss occurs. However, I did have one car with identical symptoms where fuel pressure was normal. In this (rare) case it ended up being either the crank sensor or ETA (not 100% certain, changed both and it was cured). Zero fault codes are present with all of the above scenarios.

If there is any misfiring, then it's ignition related as JC220 said. Again, no fault codes stored if it's a misfire.

I'm wondering if the fuel pump is going. Need to run the VIN as I suspect this car has the single pump being a late 95.

Check the VIN but I'd pull the cover and visually confirm before ordering pumps. If the pumps are original from 1995, it's a good idea to replace proactively anyway. I think I have replaced the pumps on every single 124 that I currently own. If you need the early dual pumps, beware of the great price on Amazon on the Bosch 69608 from a 3rd party, I just bought a pair and they arrived not in a Bosch box - I didn't want to risk it, and returned them.

 

[Ascension]

Dave yes it's perfectly smooth and when I back out of the throttle it comes back smoothly. Car has absolutely no sign of an ignition misfire. I had a shop do some work on it and they replaced the fuel filter so have never messed with the fuel system on this one. It's one of the last 034's in a 95 so may be single pump system. I need to run the VIN to make sure. Car will pull very smoothly and strong until it suddenly lays over.
Will do on taking a look at the system to confirm what it is. Guarantee if I replace pumps on this one they will be Bosch! She needs a trans build as reverse is weak plus a ETA build so I've neglected her as of late and need to get a few things sorted out soon. This is way to nice a car to not get her back right.

 

[Ascension]

Sounds like the classic m119 ignition issues

Thread 'Essential M119 Ignition "Tune Up" mods' FYI - Essential M119 Ignition "Tune Up" mods | M119 Engine

Trust me the ignition on this car is right. Have fought wars over the moisture in the distributor issues over the 8 or so years I have owned this one and know the symptoms well. She has real Duco caps and buttons new insulators ect.

 

[Ascension]

That actually does sound like fuel delivery. Almost like it’s running lean under load. Put a gage on it, it can’t hide. Did you rule out crank position sensor?

maw

Have not on the crank position would that not just shut it down? Car pulls absolutely smooth and strong until it noses over like it's running out of fuel. Back off the throttle and it will catch and come right back.

 

[gsxr]

The single-pump OEM is Pierburg, made in Poland, smaller diameter.

The dual-pump OEM is Bosch, made in Czech Republic, larger diameter.

The scenario described above with the crank sensor was extremely unusual, but as I said it acted *exactly* like a failing fuel pump. Which is why I was shocked to see fuel pressure remain at 50+ when the power loss occurred. It was truly bizarre. I didn't want to re-install the old CKP to see if any bad behavior returned. I do know all issues were cured after the CKP and ETA were both replaced. Zero fault codes on any module, nothing to indicate either item was defective, but there was some odd live data which also was cured with the new parts.

If the ETA is old/original, I'd send that to Don Roden if new pump(s) don't cure the problem. Would be nice to check fuel pressure first but you'd have to borrow or buy the hose+gauge to perform that test.

 

[maw1124]

That actually does sound like fuel delivery. Almost like it’s running lean under load. Put a gage on it, it can’t hide. Did you rule out crank position sensor?

maw

Sorry, I meant these ideas to be sequential. A gage will tell you about fuel pressure. After that, if the problem persists, CPK. If it was my car that's what the order would be. I don't think you need to be driving with the fuel gage. Revving and idle should suffice. My cars have never been driven with the gage on -- always diagnosed with the gage in the lot (no need to blow up the shops with fumes).

If no gage, I'd maybe swap the fuel filter. A partially clogged filter would also act like this (pressure, whether from throttle or thermal gets the fuel through the filter). If you've never changed the fuel filter, that's they quickest, easiest and best guess for what you describe IMO.

maw

 

[gsxr]

Unfortunately, for this particular fuel pump failure, it's a volume issue. The pumps have sufficient pressure & volume at idle, so revving in park/neutral the pressures are normal. But under load, the pressures drop as the injector duration increases and a higher fuel volume is called for. As described elsewhere on the forum, I bought a 4-foot length of AN-braided hose and an AutoMeter fuel pressure gauge that slips under the windshield wiper. With bad pumps, the gauge needle drops like a string is connected to the accelerator pedal. But it will not do this in the driveway.

Again, if the pump(s) are original from 1995, replace them on principle anyway. No point waiting for them to fail and leave you stranded. I just had original 1994 pumps spring a significant leak a few weeks ago, one of my last cars with original pumps. I was fortunate to notice it immediately (gas smell in the garage after cold start) and parked the car until I had time to fix it.

 

[maw1124]

You keep reminding me @gsxr to check to see if I'm still on original fuel pumps. Thanks again.

maw