early TBI 7.4L engines
08-28-2006, 03:05 PM
#1
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early TBI 7.4L engines Some 1988 and 1989 Chevy trucks with TBI 7.4L engines ran hot--240+--
and many engines did not make it past 10,000 miles. I bought an '88
five years ago, and it runs hot, exhibiting cherry red exhaust manifolds
even during cold weather. I have replaced everything from radiator to
tail pipe, including ECM, and it still runs hot. Any ideas, or other horror
stories? Also, 1988 K3500 7.4L's (at least) did not have knock sensors. Is it
possible to add a knock sensor?
and many engines did not make it past 10,000 miles. I bought an '88
five years ago, and it runs hot, exhibiting cherry red exhaust manifolds
even during cold weather. I have replaced everything from radiator to
tail pipe, including ECM, and it still runs hot. Any ideas, or other horror
stories? Also, 1988 K3500 7.4L's (at least) did not have knock sensors. Is it
possible to add a knock sensor?
08-29-2006, 03:41 AM
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I believe my truck is running lean, even though I have installed an aftermarket
chip to correct the "delayed power enrichment" that was designed into the factory ECM; also have added aftermarket kit to boost pressure at TBI from
spec of "9 to 11" up to 13 psi. Running a high-flow water pump and 160
degree stat as well. But the cause of running high temps is the red hot
exhaust manifolds, transferring so much heat back into the heads that the
cooling system cannot effectively dissipate it. With outside air temp of 70, driving at 55 mph yields an engine temp of 225, 65 mph = 235 and 75 mph =
245. Pull a heavy trailer on a 90 degree day and it runs 255.
chip to correct the "delayed power enrichment" that was designed into the factory ECM; also have added aftermarket kit to boost pressure at TBI from
spec of "9 to 11" up to 13 psi. Running a high-flow water pump and 160
degree stat as well. But the cause of running high temps is the red hot
exhaust manifolds, transferring so much heat back into the heads that the
cooling system cannot effectively dissipate it. With outside air temp of 70, driving at 55 mph yields an engine temp of 225, 65 mph = 235 and 75 mph =
245. Pull a heavy trailer on a 90 degree day and it runs 255.
09-03-2006, 07:45 AM
#7
Is your water pump turning in the right direction? It should be a counter clockwise pump, it will pump water if it turns the wrong direction. You can also reduce radiator bypass by putting a restriction in the heater hose, and in the hose that goes from the water pump to the intake. I'm assuming your fan is turning the right direction also?
I've seen people put clockwise fans engines with serpentine belt driven water pumps and not even realize it blows air out the radiator.
I've never heard of these problems you say, like they only last 10,000 miles.
I own a 1992 7.4 TBI Silverado dually. No problems here.
I've seen people put clockwise fans engines with serpentine belt driven water pumps and not even realize it blows air out the radiator.
I've never heard of these problems you say, like they only last 10,000 miles.
I own a 1992 7.4 TBI Silverado dually. No problems here.
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09-04-2006, 12:42 AM
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yes, the water pump turns counter clockwise...and the fan blows air back over the engine, not forward, through the radiator.
and notice that I started this thread by saying "some" 88 and 89 trucks
had this problem---some trucks are not affected, and later models with TBI are excluded. The same ECM is used in them all, however.
I have talked to owners who bought these trucks when they were new.
they ran hot, especially when towing, and most got rid of them. I was
unlucky enough to have bought a used one--when it was 10 years old--
and I am determined to find a fix as I have a lot of time and money invested.
and notice that I started this thread by saying "some" 88 and 89 trucks
had this problem---some trucks are not affected, and later models with TBI are excluded. The same ECM is used in them all, however.
I have talked to owners who bought these trucks when they were new.
they ran hot, especially when towing, and most got rid of them. I was
unlucky enough to have bought a used one--when it was 10 years old--
and I am determined to find a fix as I have a lot of time and money invested.
09-04-2006, 06:23 AM
#10
yes, the water pump turns counter clockwise
my truck has an '88 engine in it with 7000 original miles, actually just the long block, it has the '92 TBI and the brackets.
09-04-2006, 10:12 AM
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[QUOTE=8a8mfh]but you've replaced it with...did you verify it was a ccw pump? QUOTE]
Water pump is genuine GM, bought at the dealership, part number verified and double-checked...wouldn't think I would have to take off the back cover
to make sure it was the right pump. At one time, I had an after-market, high-flow water pump on it (forgot the brand)--but the housing on it was broken
when the original crankshaft pulley, kind of a "cone-shaped" one, disintegrated (at 35 mph), which also took out the serpentine belt and put
shrapnel in my new radiator. The replacement crankshaft pulley is built with
a different, stronger design, but when it came in, the tech said it wouldn't fit---so I spent an hour with a rat tail file enlarging the center hole enough so that it would fit. Anyway, hope your '88 block has been updated with the new-style pulley.
Water pump is genuine GM, bought at the dealership, part number verified and double-checked...wouldn't think I would have to take off the back cover
to make sure it was the right pump. At one time, I had an after-market, high-flow water pump on it (forgot the brand)--but the housing on it was broken
when the original crankshaft pulley, kind of a "cone-shaped" one, disintegrated (at 35 mph), which also took out the serpentine belt and put
shrapnel in my new radiator. The replacement crankshaft pulley is built with
a different, stronger design, but when it came in, the tech said it wouldn't fit---so I spent an hour with a rat tail file enlarging the center hole enough so that it would fit. Anyway, hope your '88 block has been updated with the new-style pulley.
09-04-2006, 08:45 PM
#12
You could try www.454ss.com theres a lot of knowledgable people over there when it comes to the TBI big blocks.
