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2004 Cadillac Deville idle

Tiny
SUPERMAN726
  • MEMBER
  • 2004 CADILLAC DEVILLE
  • 4.6L
  • V8
  • FWD
  • AUTOMATIC
I have a 2004 cadillac deville with the 4.6 Northstar motor. The car started to stumble and stall and hesitate then all of a sudden the engine started to race and run at like 2000-2500 rpm we did find a vacuum leak and fixed that. We tried another TPS, IAC, cleaned the throttle, and checked the codes. It is giving codes p0121, p0171, and po174, and p1101. Can someone please help?
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Friday, March 20th, 2015 AT 6:09 PM

11 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
I would probably monitor the fuel pressure at the moment this is occurring. Indications are that the system is going lean for some reason and losing fuel pressure would be a likely cause.
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Saturday, March 21st, 2015 AT 4:23 AM
Tiny
SUPERMAN726
  • MEMBER
  • 12 POSTS
I will hook up a gauge to that today I didn't even think of that. What should it be? About 40-50 right? Also I'm trying to bench test the TPS, MAP, MAF, AND IAC can someone give me these specs and how to test them? Maybe a direction of a website on these specs and instruction. Also could the EGR or EVAP be doing this? I'm beginning to think it's the ECM and I'm not happy.
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Saturday, March 21st, 2015 AT 7:42 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
The fuel pressure spec for that engine is 41 - 47 PSI.

As far as other diagnostic info you can get a single vehicle subscription to www. AlldataDIY. Com for a very reasonable price. That is the same data service we use in the professional version.
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Saturday, March 21st, 2015 AT 7:52 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
You also want to clear all those codes to see which ones come back. You may have unplugged something and turned the key on and that would have set some of those codes.
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Saturday, March 21st, 2015 AT 7:53 AM
Tiny
SUPERMAN726
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  • 12 POSTS
I tested the fuel pressure and it was very erratic and leveled out at about 38psi running. When I shut the car off it went up to 40 and stayed there till I released it. Once I released it for some reason it continually had a little pressure even with the car off. Could a vacuum leak send all these sensors into a fault and make the engine race like this. The car won't idle normal it is always idling at like 2000 rpms.
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Saturday, March 21st, 2015 AT 1:18 PM
Tiny
SUPERMAN726
  • MEMBER
  • 12 POSTS
I tested the fuel pressure and it was very erratic and leveled out at about 38psi running. When I shut the car off it went up to 40 and stayed there till I released it. Once I released it for some reason it continually had a little pressure even with the car off. Could a vacuum leak send all these sensors into a fault and make the engine race like this. The car won't idle normal it is always idling at like 2000 rpms. The most recent codes were p02l121, p0171, and p0174. How would I clear the computer (I do have a pocket scan tool) and if I cleared the computer by pulling the fuse for 5 minutes do I have to reprogram it or something?
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Saturday, March 21st, 2015 AT 1:20 PM
Tiny
WRENCHTECH
  • MECHANIC
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Why are you still talking about sensors? You just proved the fuel pressure is too low.
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Saturday, March 21st, 2015 AT 1:20 PM
Tiny
SUPERMAN726
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Last night we decided to take a gamble and we pulled the intake manifold. Thank god we did there was a hole in the throttle body to intake coupling and we also found an injector that the pintle cap was broken on. We had to use a vacuum with a small hose on it to get the pintle cap out of the engine and we replaced everything. The car is now running 100% better. Thank you for your help and if y'all ever hear of a cadillac 4.6 Northstar racing up to like 2000 rpm have the owner or Mechanic look at the throttle body to intake manifold coupling. You can mark this one as solved.
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Sunday, March 22nd, 2015 AT 8:04 AM
Tiny
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Oh and the fuel pressure is back to normal.
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Sunday, March 22nd, 2015 AT 8:05 AM
Tiny
WRENCHTECH
  • MECHANIC
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I suspect the fuel pressure problem was more of a faulty gauge than an actual problem. What you found didn't have any effect on fuel pressure. Glad you found the problem though.
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Sunday, March 22nd, 2015 AT 8:07 AM
Tiny
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I tested the fuel pressure this morning and it was right around 40psi.
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Sunday, March 22nd, 2015 AT 2:29 PM

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