No Top End Power
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Logistics Pro
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From: Brandon, MB
No Top End Power
I've got a '93 4.0 AWD with 180k and in the last 3-4k I've completely lost all top end power. Lots of bottom end grunt though. I changed the fuel filter, gutted the cats, checked the spark plugs (no fun at all), and am now thinking MAF sensor? Any other ideas? Oh yeah, I had the O2 sensor changed as well. And the air filer is still good too.
Thanks
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Posting Guru
Joined: Jul 2004
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From: Mitchell, SD
Originally Posted by Fullcrew7.3
I changed the fuel filter, gutted the cats, ....and am now thinking MAF sensor? Any other ideas?
That is a very bad thing to do (and illegal.)
I am leaning towards two ideas of your lack of high end power. 1, Sense you gutted the cats, you have reduced your exhaust velocity (how fast the exhaust moves through the pipes) so you have less HP (but more TQ.) 2. You dropped some cat pieces down the pipe and they are obstructing exhaust gasses from leaving causing a loss of HP because the engine has to work harder to expell the gasses.
BTW are you getting a CE light. Instead of throwing parts at it (which looks like you have been doing) I would do some more investigating.
FTE Community Team
Joined: Nov 2001
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From: Oak Harbor, Washington
Originally Posted by Fullcrew7.3
I've got a '93 4.0 AWD with 180k and in the last 3-4k I've completely lost all top end power.
Can you perform a fuel pressure test at the fuel rail's test port (use a cheap air compressor gauge, <$10 at a hardware store, some high-pressure fuel line, a hose barb, two hose clamps, and a Schrader valve removal tool (like for a bicycle tube))?
Do you have a "Check Engine" light?
Regards,
Al S.
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Joined: Jun 2003
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From: SW VA
Originally Posted by 93nighthawk
1, Sense you gutted the cats, you have reduced your exhaust velocity (how fast the exhaust moves through the pipes) so you have less HP (but more TQ.)
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Logistics Pro
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From: Brandon, MB
I hadn't thought of CLEANING the MAF. I'll try that one. As for the Cat, Provincial regulations where I'm at are such that on '93 and older vehicles, they are not required to be maintained. Don't ask me why, I can't answer that one. As for exhaust flow, It is nicely increased. I did check that. The front was was partially plugged. the back one seemed pretty good, but took it out anyway.
The O2 sensor was changed before I ran into this problem. Shortly I was getting a CE light,so I took the van in and had the codes read. They all pointed to air flow. The mechanics(2 of them) both recomended gutting the cat as a cheap first step. The MAF was next.
I'll have to check the fuel rail. I did similar on my F350 and had to adjust it, so that could be similar. What fuel pressure should I be seeing?
As for under load and revving, yes it does run smooth. It has a distinct hesitation when throttle applied. Especially when punched. It does have a bit of a rough idle, but it's had that since I got it 3 years ago.
Thanks for the help.
The O2 sensor was changed before I ran into this problem. Shortly I was getting a CE light,so I took the van in and had the codes read. They all pointed to air flow. The mechanics(2 of them) both recomended gutting the cat as a cheap first step. The MAF was next.
I'll have to check the fuel rail. I did similar on my F350 and had to adjust it, so that could be similar. What fuel pressure should I be seeing?
As for under load and revving, yes it does run smooth. It has a distinct hesitation when throttle applied. Especially when punched. It does have a bit of a rough idle, but it's had that since I got it 3 years ago.
Thanks for the help.
Former ******
Joined: Nov 2004
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From: Salt Lake City, Utah
Gutting the cats is illegal. Also,m the above post got it crossed. Haveing a straight through exhaust is good for high end power, because the airflow is increased, but without any backpressure, the torque goes to pot. However, the low back pressure can really mess with your o2 sensor, and if the cat was plugged, that means your vehicle has been running poorly for a very long time. Rough idle may suggest a complete tune up is due. I would get all tune up items taken care of before worrying about the MAF. Just spray that out with TB cleaner. Get new High flow cats installed.
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FTE Community Team
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From: Oak Harbor, Washington
It may not be illegal to gut cats where he lives (ie not in USA). His current symptom is not going to be affected by the lack of cats, so let's move on.
Can you post the exact codes exhibited. This will be more helpful than your two mechanics' interpretation of them -- after all, they didn't actually FIX the problem, did they? So let US have a shot at it
Fuel pressure: according to Alldata:
Key On, Engine Off: 35-45 PSI
Engine running: 30-40 PSI
Regards,
Al S.
Can you post the exact codes exhibited. This will be more helpful than your two mechanics' interpretation of them -- after all, they didn't actually FIX the problem, did they? So let US have a shot at it
Fuel pressure: according to Alldata:
Key On, Engine Off: 35-45 PSI
Engine running: 30-40 PSI
Regards,
Al S.
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Logistics Pro
Joined: Jan 2005
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From: Brandon, MB
I stil haven't had a chance to check the fuek pressure, but will get to that when I can. Wouldn't low/or high fuel pressure throw a code though?
Anyway, sorry to take so long getting back with codes I did get. GHad to find the slip of paper they were written on.
114
172
185
186
Actauly, I have a question about 172. I was just looking it up againa and I noticed that it also could be vacuum related. That I'll have to check as well.
As for 114, it was just around new years when I had the codes read, so the ambient temp was pushing -35C without the wind.
Thanks again for the help
Anyway, sorry to take so long getting back with codes I did get. GHad to find the slip of paper they were written on.
114
172
185
186
Actauly, I have a question about 172. I was just looking it up againa and I noticed that it also could be vacuum related. That I'll have to check as well.
As for 114, it was just around new years when I had the codes read, so the ambient temp was pushing -35C without the wind.
Thanks again for the help
Junior User
Joined: Aug 2003
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From: North of Pittsburgh
Your symptoms sound very similar like my 1991 Aero 4L AWD a couple of years ago. It would idle smooth; you could rev it up fine, however when revving it up under load, it would run rough. Turned out the spark plug wires needed changed. After that and a new set of vacuum lines, it ran like new. I changed the plugs before the wires. Should have changed them at same time.
XrayJock
XrayJock
FTE Community Team
Joined: Nov 2001
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From: Oak Harbor, Washington
Plug wires seem to be a very common failure item on both the 3.0l and 4.0l, but moreso on the latter. However, you have smooth running when under load and revved, just lacks power. Hmmm.
When my fuel pump was failing, no CEL occured. I had to pick it up via the fuel rail pressure test, and it was a good 10 PSI low and fluctuating.
The 185/186 sure would have me looking at fuel pressure and the fuel filter. You've already done the filter. You must check the fuel pressure now. Good luck!
Regards,
Al S.
When my fuel pump was failing, no CEL occured. I had to pick it up via the fuel rail pressure test, and it was a good 10 PSI low and fluctuating.
The 185/186 sure would have me looking at fuel pressure and the fuel filter. You've already done the filter. You must check the fuel pressure now. Good luck!
Regards,
Al S.
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Logistics Pro
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From: Brandon, MB
I'm getting just over 30 psi at idle. I didn't check under load.
I was thinking about getting plug wires anyway, but now I have too. Pulled one apart getting them off to check the plugs. Guess I might as well do the plugs too. I'll let you know how it goes.
asavage- was the fuel pressure fluctuating at idle/underload? Just wondering as I only checked at idle. Haven't got a guage yet, just checked with a handheld.
I was thinking about getting plug wires anyway, but now I have too. Pulled one apart getting them off to check the plugs. Guess I might as well do the plugs too. I'll let you know how it goes.
asavage- was the fuel pressure fluctuating at idle/underload? Just wondering as I only checked at idle. Haven't got a guage yet, just checked with a handheld.
FTE Community Team
Joined: Nov 2001
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From: Oak Harbor, Washington
On mine, I stopped testing when I had low idle pressure, so I can't answer that. Generically, if the pressure is good at idle, and I still suspect fuel delivery, I do a volume test: can you get a pint in 30 secs? Harder to do on our rigs without the diverter valve setup.
A fouled fuel filter can yield good low-volume pressure and poor high-volume pressure. Unrelated to your problem, but a restricted fuel filter can contribute to accelerated fuel pump wear, because the pressure between the pump and the filter can run higher than the fuel pressure regulator setpoint, and that's more work the pump has to do -- all the time it's running.
A fouled fuel filter can yield good low-volume pressure and poor high-volume pressure. Unrelated to your problem, but a restricted fuel filter can contribute to accelerated fuel pump wear, because the pressure between the pump and the filter can run higher than the fuel pressure regulator setpoint, and that's more work the pump has to do -- all the time it's running.
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