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94 chevy C2500 engine rattle


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Flash32
New User

Oct 21, 2010, 10:55 PM

Post #1 of 3 (1812 views)
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94 chevy C2500 engine rattle Sign In

94 5.7 TBI, started what sounds like an ignition rattle. Engine only makes the noise under a load when accelerating.
I have changed MAP sensor, TPS, knock sensor, new plugs, cap, rotor, wires, fuel pump, fuel filter & even the ECM! I checked the timing by letting truck warm up, disconnecting the tan/black wire & setting timing to 0. Plugged the wire in & re-checked timing. Checked the valvetrain with valve covers off & found everything to be fine there. Checked the fuel "cone" with a timing light & it seems even.

Now when trying to start the engine when its cold, it won't start until I pour a little gas in the TB, then it runs ok. After the engine is warm & try to re-start, it starts ok. But still rattles under a load, won't rattle while raising rpm's sitting still.

Motor has 140,000 mi. Could this be a TB problem? New to the forum & after reading some of the posts, seems like there are many that have very good solutions on here!

Thanks in advance & hope I covered everything!


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Oct 22, 2010, 5:37 AM

Post #2 of 3 (1808 views)
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Re: 94 chevy C2500 engine rattle [In reply to] Sign In

A few things that will cause that.

  1. Excessive lean fuel mixture from low fuel pressure or clogged injectors
  2. Inoperative EGR system
  3. Advanced ignition timing
  4. Overheating





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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Oct 24, 2010, 2:03 PM

Post #3 of 3 (1797 views)
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Re: 94 chevy C2500 engine rattle [In reply to] Sign In

Yes - all of what HT suggested. Since you have to prime this cold to start it there's a big clue. Takes some guessing as calling it an ignition based noise is a bit confusing so far to me. Having to prime it needs be tended to first as it's possible the thing is trying to compensate for low fuel pressure.

Once that is all set if it still makes this noise then it's open book of possibilities. One way if you have competent help could be to block wheels, set parking brake hard, hold brakes and put a load on it in place (stand to side of vehicle not in front) and you might with hood open find it's an accessorie.

Some other things on the maybe list to check since I'm just not sure nor are you:

*Take belt off and do that apply load thing. If noise is gone and was there with belt on there's the clue for the noise if that at all.

* Check (engine off keys out) the free play if any with fan clutch and or waterpump.

* Oddly - sometime type of fan belt, brand of fan belt can be noisy suckers with nothing really wrong. Had one that sounded like hell brand new making noises like real problems were happening and it was only that belt. Did it within 5 miles! Next belt has been quiet for years. pulleys get shinny with age and miles and if that there are belts known to stay quiet even with that condition so long as there isn't a real problem with a pulley,

T
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