3.8L Hiccups
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3.8L Hiccups
Got a really weird problem, and have had it since the old Duck was about 5 years old (obviously, out of warranty).
1986 Thunderbird, 3.8L, CFI, C5 3-speed
Problem: Intermittent surging when at switchover temperature (open loop to closed loop)
When cold, it runs like a champ. If I can make it to the interstate before it reaches "switchover" temperature, I don't have the problem. Sometimes, don't have the problem at all on a hot summer day if the temp climbs quickly. If I get stuck in normal traffic, the old bird runs cool enough that it seems to hover around the switchover temperature, at at least this is my theory. The problem occurs under light throttle, like just maintaining speed, or easing off from a light, following traffic, etc. A small change in throttle, and it's like the fuel injectors just shut off. If I stick my toenails in the main bearings (WOT)though, it'll take off like a scalded dog. Just holding the throttle constant, and it starts surging like the injectors are switching on and off (not pulsing when they should be), and acting like it's running out of fuel. I've checked fuel pressure, it's fine. FPR is built into the TBI assembly, and I'm not having any flooding issues, so I'm assuming it's OK.
This engine has been plagued by coolant and oil leaks forever. The ex overheated the original engine once when the bypass hose blew. That started the initial leaking by cooking most of the gaskets. It had the top off the original engine several times for coolant and oil leaks on the intake, and I have to wonder if perhaps the connectors for the ECT and ACT have been swapped somewhere along the line. (Anyone got EEC-IV wiring diagrams for the '86 T-Bird?) The connectors are identical, and the two are very close proximity to each other. Could this cause the toggling back and forth between open loop and closed loop modes, and perhaps opening things that should not be opened, and causing the surge. Engine's got excellent vacuum (about 19 inches) at idle. The intake and exhaust manifolds, however, are about the only original parts left of the engine. One episode with intake leaking resulted in a rag being left under the intake, wrapped around the cam, and thoroughly trashing an engine with only 63000 original miles. August, two years ago, I had a long block installed by a dealer, which is a whole other story.
As long as I'm running highway speeds, it runs like a champ. When I get off the interstate, and run about a mile or two, that's when the surging starts again. The only common factor I've noticed is that the temperature drops back down a bit, and I'm guessing it's right at the switchover temperature. The t-stat is a brand spankin new 195 degree Motorcraft. I put a new radiator in it because one I put in about 8 years ago was leaking pretty badly at one of the headers. I seem to have remedied all the leaks except one weeping oil leak where the dealer that installed the new long block used the side of a can or something to block off the hole for a mechanical fuel pump on the timing cover.
Is this a problem that electric fans could solve by raising the coolant temperature a little, say to 200 before letting the cooling fans come on? (would love to get rid of the airplane propeller it uses for a fan, and get some HP's back) This car is going to be a project car for me. I bought it new in December of '85, and it's got a lotta sentimental value to me, but is worthless for trade-in. Electric fans seem like a good idea for faster warm up, and should give the CFI engine a few ponies back. I need all I can get with a V6 in a 3900 pound car. Would a system with dual sensors, one on the block, and one in the radiator be a bonus, or just more complication? I've had the fan clutch lock up on it once, and the noise was very impressive. I couldn't tell if the fan was pulling the car, or if the transmission was pushing it.
Of particular note, when it surges, if I back off the throttle, it picks back up for a second, then surges again. It NEVER dies while idling, and in fact, idles like a dream.
Me and a lot of other 'mechanics' have been chasing this problem for a very long time (most of the life of the car), and I've checked everything I can think of. However, with no wiring diagrams, I can't guarantee the ACT and ECT are not swapped, or that everything is as it should be.
Thanks for any ideas or suggestions in advance.
1986 Thunderbird, 3.8L, CFI, C5 3-speed
Problem: Intermittent surging when at switchover temperature (open loop to closed loop)
When cold, it runs like a champ. If I can make it to the interstate before it reaches "switchover" temperature, I don't have the problem. Sometimes, don't have the problem at all on a hot summer day if the temp climbs quickly. If I get stuck in normal traffic, the old bird runs cool enough that it seems to hover around the switchover temperature, at at least this is my theory. The problem occurs under light throttle, like just maintaining speed, or easing off from a light, following traffic, etc. A small change in throttle, and it's like the fuel injectors just shut off. If I stick my toenails in the main bearings (WOT)though, it'll take off like a scalded dog. Just holding the throttle constant, and it starts surging like the injectors are switching on and off (not pulsing when they should be), and acting like it's running out of fuel. I've checked fuel pressure, it's fine. FPR is built into the TBI assembly, and I'm not having any flooding issues, so I'm assuming it's OK.
This engine has been plagued by coolant and oil leaks forever. The ex overheated the original engine once when the bypass hose blew. That started the initial leaking by cooking most of the gaskets. It had the top off the original engine several times for coolant and oil leaks on the intake, and I have to wonder if perhaps the connectors for the ECT and ACT have been swapped somewhere along the line. (Anyone got EEC-IV wiring diagrams for the '86 T-Bird?) The connectors are identical, and the two are very close proximity to each other. Could this cause the toggling back and forth between open loop and closed loop modes, and perhaps opening things that should not be opened, and causing the surge. Engine's got excellent vacuum (about 19 inches) at idle. The intake and exhaust manifolds, however, are about the only original parts left of the engine. One episode with intake leaking resulted in a rag being left under the intake, wrapped around the cam, and thoroughly trashing an engine with only 63000 original miles. August, two years ago, I had a long block installed by a dealer, which is a whole other story.
As long as I'm running highway speeds, it runs like a champ. When I get off the interstate, and run about a mile or two, that's when the surging starts again. The only common factor I've noticed is that the temperature drops back down a bit, and I'm guessing it's right at the switchover temperature. The t-stat is a brand spankin new 195 degree Motorcraft. I put a new radiator in it because one I put in about 8 years ago was leaking pretty badly at one of the headers. I seem to have remedied all the leaks except one weeping oil leak where the dealer that installed the new long block used the side of a can or something to block off the hole for a mechanical fuel pump on the timing cover.
Is this a problem that electric fans could solve by raising the coolant temperature a little, say to 200 before letting the cooling fans come on? (would love to get rid of the airplane propeller it uses for a fan, and get some HP's back) This car is going to be a project car for me. I bought it new in December of '85, and it's got a lotta sentimental value to me, but is worthless for trade-in. Electric fans seem like a good idea for faster warm up, and should give the CFI engine a few ponies back. I need all I can get with a V6 in a 3900 pound car. Would a system with dual sensors, one on the block, and one in the radiator be a bonus, or just more complication? I've had the fan clutch lock up on it once, and the noise was very impressive. I couldn't tell if the fan was pulling the car, or if the transmission was pushing it.
Of particular note, when it surges, if I back off the throttle, it picks back up for a second, then surges again. It NEVER dies while idling, and in fact, idles like a dream.
Me and a lot of other 'mechanics' have been chasing this problem for a very long time (most of the life of the car), and I've checked everything I can think of. However, with no wiring diagrams, I can't guarantee the ACT and ECT are not swapped, or that everything is as it should be.
Thanks for any ideas or suggestions in advance.
