87 F150 sputtering at tip in
01-28-2008, 11:50 AM
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87 F150 sputtering at tip in
All,
I've got an 87 F150 with a new fuel system (every part is new - no joke), 40 psi fuel pressure, timing is set correct (10 BTDC), new sensors (MAP, O2 sensor, IAC, TPS), new FPR, 21 in vacuum at idle, EGR valve is good, EVP sensor is good. When you tip in on the throttle, the engine sputters badly and spark knocks some, but will correct itself if you press harder on the throttle. It seems to be running rich (very dark plugs) and the IAC has the motor idling at 1500 rpm. The TPS is set at .98V at idle. The truck will idle fine if you unplug the IAC. With the IAC unplugged and the spout unplugged, the truck will still sputter and die under very light throttle. I'm thinking computer since it is rich, spark knocking, and has the IAC turned up. Any thoughts are appreciated. Thanks.
Jeff
I've got an 87 F150 with a new fuel system (every part is new - no joke), 40 psi fuel pressure, timing is set correct (10 BTDC), new sensors (MAP, O2 sensor, IAC, TPS), new FPR, 21 in vacuum at idle, EGR valve is good, EVP sensor is good. When you tip in on the throttle, the engine sputters badly and spark knocks some, but will correct itself if you press harder on the throttle. It seems to be running rich (very dark plugs) and the IAC has the motor idling at 1500 rpm. The TPS is set at .98V at idle. The truck will idle fine if you unplug the IAC. With the IAC unplugged and the spout unplugged, the truck will still sputter and die under very light throttle. I'm thinking computer since it is rich, spark knocking, and has the IAC turned up. Any thoughts are appreciated. Thanks.
Jeff
01-28-2008, 09:12 PM
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Ok - just a few basic questions - don't mean to offend, you seem to be mechanically inclined - just need a little more info:
Did you pull the SPOUT connector when setting the timing?
Is the MAP sensor correct for the motor?
Any 'check engine' fault codes?
Certain there are no vacuum leaks anywhere?
Does the TPS voltage change smoothly with the throttle changes?
Did you pull the SPOUT connector when setting the timing?
Is the MAP sensor correct for the motor?
Any 'check engine' fault codes?
Certain there are no vacuum leaks anywhere?
Does the TPS voltage change smoothly with the throttle changes?
01-30-2008, 07:39 AM
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WDE,
The spout was out, there are no vacuum leaks that I can find, the TPS transfers from .98V to 4.5V evenly, and according to the old analog voltmeter sweep test, there are no codes (seemed strange to have no codes - I thought it might be another symptom of a bad computer - no entry into self test). As far as the MAP goes, it is correct according to the parts store. When I first put it on the truck, you could unplug the vacuum line and the truck would black smoke (normal response). Now, it doesn't do anything at all when you unplug the vacuum line. So the question is - computer can't read the MAP input, computer is sending the wrong output regardless of MAP input, or is the new MAP I put on bad? I ran out of time last night and didn't get to check the MAP signal - I'll have to do that tonight.
The spout was out, there are no vacuum leaks that I can find, the TPS transfers from .98V to 4.5V evenly, and according to the old analog voltmeter sweep test, there are no codes (seemed strange to have no codes - I thought it might be another symptom of a bad computer - no entry into self test). As far as the MAP goes, it is correct according to the parts store. When I first put it on the truck, you could unplug the vacuum line and the truck would black smoke (normal response). Now, it doesn't do anything at all when you unplug the vacuum line. So the question is - computer can't read the MAP input, computer is sending the wrong output regardless of MAP input, or is the new MAP I put on bad? I ran out of time last night and didn't get to check the MAP signal - I'll have to do that tonight.
01-31-2008, 08:57 AM
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Well - the new MAP was bad. I tested it, it didn't change frequency, so I shotgunned a new one in and it fixed the problem. I sure wish I knew why new parts go bad - lowest bidder on the contract I guess. Thanks guys for the help.
Jeff
Jeff