Loss of power

R

Rabid Sloth Racing

Active Member
Hey all,

I'm having some bad power loss issues. The car has always run better with the MAF disconnected but last night it started running really rough. After about an hour of cruising around just fine it started sputtering under WOT and finally died to the point i thought I had run it out of gas. After filling it up it was very hard to start and had a dramatic loss of power anywhere over ~25% throttle. I limped it home and took the video below. the only codes that were thrown were P0443, P0449, P0452, and P0300. As hot as it was I didn't really feel like working on it, so I let it sit overnight. This evening when I went out it was still very hard to start, idled weakly, and was running rough when it did start. I did a quick loop around the block and from idle to ~1750 rpm its rough. then up to any rpm and very little throttle it will move. It I give it much more than ~25% of the pedal it dies again. Tonight there was no P0300 code, but all the others are still there. I tried it with and without the MAF connected with the same results.

I'm hoping someone might have ideas before I start tearing into it.

The fuel filter only has ~50 miles on it. Just put a new MAF in. I went borderline psycho when doing the grounds. From a quicklook I don't see any loose connections...


 
Rttoys

Rttoys

Goblin Guru
The first 3 codes are evap, so they don’t matter. P0300 is “random misfire“ but you probably already know that.

can you look at the data stream at all? Map readings, o2, coolant Fp temps! Etc?
 
Rttoys

Rttoys

Goblin Guru
Well hell. Seeing the data stream is very helpful. Well, it’s a double edged sword; the data can be very helpful in diagnosing, but you have to be able know what you are looking at too. o_O
 
Ross

Ross

Goblin Guru
Do you have a pointer temp gauge thingy that you can point at each exhaust port?
Pull the plugs. Do they all look the same?
Check compression. It does sound like spark, but at least it would rule out a mechanical issue.
 
ccannx

ccannx

Goblin Guru
Is your Goblin is still running after you pull the ignition key. Seems almost as if there is un-burnt fuel , injector leak or trash in the injector allowing the engine to keep running.
 
Last edited:
ctuinstra

ctuinstra

Goblin Guru
First if the car is running better with the MAF unplugged, there were some real underlying issues that needed to be addressed. That forced the car to run strictly off the VE table. Also with it unplugged, it couldn’t read the intake air temps so it probably assumed the coldest all the time and run very rich. Running that rich could have fouled the O2 sensor making issues worse. It seems as if it snow-balled on you. You may be looking at multiple problems at this point in not just one issue.

Sorry this seems so negative and isn’t really helping to solve it. You are going to have to get more diagnostic tools to get to the solution quick otherwise it’s just a bunch of guesses along the way.

I’m surprised you aren’t logging P0100,102,103 codes if the MAF is unplugged.
 
R

Rabid Sloth Racing

Active Member
It ran better off the tables, but I mostly ran it with the MAF connected. The MAF housing had a small crack in the plastic which was what I thought was causing the issue to start with. Generally it would run best when it was cool and get worse as it was driven. I replaced the MAF just before the last drive and it was running mostly fine up until the car died.

The original upstream O2 sensor looked like junk when I pulled it from the donor, a ton of that rusty looking build-up. I had forgotten to swap it out, but as of tonight there's a new upstream O2 in it. Still runs rough. I haven't changed the downstream one.

Swapped the old spark plugs after doing the O2 sensor. The original ones didn't have a ton of electrode left but looked similar. I don't have a gas engine compression tester to check that. Still runs rough...

How are these old fuel pumps when they get to or near empty. Do they ever self disintegrate? If so would I expect a pump or rail pressure code? Volume and pressure aren't the same, but could I pull the line post filter, jump the pump relay, and check flow rates as a first pass?

I bet the coils are original with ~120k miles on them, but if they are going would I expect to always get a P0300, not just the one time?

As for it running after the key is pulled I think I remember someone on here tracking that down to the new heat exchanger fan supplying current as it spools down.

Maybe it's time to get a copy of HP tuners?
 
Karter2026

Karter2026

Goblin Guru
1. I bet the coils are original with ~120k miles on them, but if they are going would I expect to always get a P0300, not just the one time?

Coils should give a definite cylinder if they are bad. Like a P0302 , P0304 etc. A P0300 can be caused by multiple things it is sort of a generic code in my opinion.

2. The original upstream O2 sensor looked like junk when I pulled it from the donor, a ton of that rusty looking build-up. I had forgotten to swap it out, but as of tonight there's a new upstream O2 in it. Still runs rough. I haven't changed the downstream one.

Just unplug the downstream o2 you do not need it unless you are running a CAT It will still throw codes even with it plugged in and no CAT.
3.
As for it running after the key is pulled I think I remember someone on here tracking that down to the new heat exchanger fan supplying current as it spools down.

Look back through Baltimorehokies build I think he had to put a resistor in some place to stop this same thing.

Just my 2¢
 
ctuinstra

ctuinstra

Goblin Guru
Agree with Karter. You don’t need the second O2. I don’t think that will change anything but having it plugged in is telling your PCM that the cat is bad.

Investing HP Tuners may be the way to go. Not only can you do a scan with it to “see” what is happening, you can adjust for differences in your set up as compared to the Cobalt setup.

If you have changed your intake plumbing much from stock, that will throw off the MAF really bad. Most likely that’s why with the MAF plugged in, it doesn’t run well.

In HP Tuners, you can turn off many things that have to do with the cat. I also eliminated many things that have to do with the A/C compressor load. It can be a very useful tool (if you know how to use it, I’m still learning).
 
Ross

Ross

Goblin Guru
My MAF sensor won't read correctly if the air filter is mounted too close to it.
I have to back the air filter up until it barely catches the intake tube, then it reads better.
15435
 
DCMoney

DCMoney

Goblin Guru
Karter2026 said:
3.
As for it running after the key is pulled I think I remember someone on here tracking that down to the new heat exchanger fan supplying current as it spools down.

Look back through Baltimorehokies build I think he had to put a resistor in some place to stop this same thing.

Just my 2¢
Click to expand...
Diode fixes the engine running after key is pulled issue.

dfkitcar.com

Manny's City Goblin - 07 SS/SC Donor

Seems to be a common problem, as several other build threads also indicate getting only 3psi boost after getting their cars on the road. You may want to search for them to see what remedies may have been implemented. I figured it out. It was a solenoid that I removed thinking it was part of the...
dfkitcar.com dfkitcar.com
 
ctuinstra

ctuinstra

Goblin Guru
Ross said:
My MAF sensor won't read correctly if the air filter is mounted too close to it.
I have to back the air filter up until it barely catches the intake tube, then it reads better.
Click to expand...
I agree with Ross. That was the first thing my tuner commented on when he seen the car. It's one of the things on my list to do. Remount and lengthen the air path before the MAF. I just can't seem to find a good source for the 3" aluminum pipe and fittings. Anyone have a source?
 
Karter2026

Karter2026

Goblin Guru
ctuinstra said:
I agree with Ross. That was the first thing my tuner commented on when he seen the car. It's one of the things on my list to do. Remount and lengthen the air path before the MAF. I just can't seem to find a good source for the 3" aluminum pipe and fittings. Anyone have a source?
Click to expand...
Frozen Boost is one place you can find them. Also ebay
 
ctuinstra

ctuinstra

Goblin Guru
They do have a few pieces. The one was a group of pieces of different bends, but it's out of stock. I need to figure out how I want to do it first. Also, I which they had a long piece with the MAP mount welded to it.
 
Lonny

Lonny

Administrator
Staff member
Ross said:
My MAF sensor won't read correctly if the air filter is mounted too close to it.
I have to back the air filter up until it barely catches the intake tube, then it reads better.
View attachment 15435
Click to expand...
Ross is correct, if the filter is pushed too far on it causes the air to tumble and confuses the MAF sensor.
Intake air filter_0.jpg
 
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