Incomplete exhaust......really poor idle....I'll explain

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Cochip

New Member
Nov 29, 2010
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Caldwell, Idaho
Hey there everyone I need your assistance. First off I'll let you all know that I currently drive a 1994 Toyota pickup :aigo:, but wait before you click off this thread I'll have you know there is a 7MGE out of a 1988 Supra living there. Better? Good. Now I need some piece of mind. I just recently transplanted the ol girls heart with a better one and haven't yet had the exhaust completed, lack of welding skills or equipment. My hope was to limp her down the road a couple of miles and have the experts do it for me, however she won't stay running. Now I didn't expect the engine to purr like a kitten or anything of the sorts, but I did figure she'd run enough. I was wrong. She'll fire right up and initially high idle well and I can give her some gas and she'll rev up real nice. But within thirty seconds or so the engine will drop down rpms quick, no matter how high the idle is at the time and with gas being applied, and then she'll gallop and studder. If I give her some gas during that time she'll die, everytime, without fail. Is this just the lack of a complete exhaust? If so that'd make me happy, I'll just get her towed down the way and presto, I have a sweet truck. If not the exhaust, any thoughts? The engine has 142k on the odo and ran smooth when she was removed to be replaced by a 7MGTE. Thanks ahead of time and thanks for reading this. :thumbup: Oh I almost forgot the only change I made to the engine was to install EGR blockoff plates that I purchased from Driftmotion.

1994 Toyota Pickup 4X4, 1988 7MGE Engine

PS: I looked around for this one online first, but no answers were found. The oil pan on the engine is out of a Cressida, front sump and it has a plastic plug in it as well as the traditional drain plug. What is that plastic plug? Is there a function for it? I've seem to have found a donor pan with a plastic plug that has a slight weep from around the edges of it so I wonder if it is able to be replaced or are there treads in there and can I just remove it and run a bolt up in there instead? Just couldn't find an answer on this one. Thanks
 
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C

Cochip

New Member
Nov 29, 2010
31
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Caldwell, Idaho
AJ'S 88NA;1652379 said:
Have you adjusted the TPS?
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No adjustments whatsoever. I was wondering if that could be a potential issue. I didn't want to go and adjust anything just yet. I'll have to give that a look once I get the exhaust finished up tomorrow afternoon. I was wondering, I got a donor throttle cable from another supra, close in model year, because the throttle cable on the truck was crazy long! I don't know but would that place the throttle in the wrong position and cause this problem?
 
C

Cochip

New Member
Nov 29, 2010
31
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Caldwell, Idaho
slow_yota;1652408 said:
Hopefully the exhaust was there [enough anyways]
so no cold air could get up under the valves and warp them..
Cause they will warp pretty fast in this cold weather.
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I read up a bit on this and I believe I was okay there. I was in the garage for the test fire and since I have added as much of the next section of exhaust as would fit. I'm gonna get it to the exhaust shop tomorrow and I'll see how it acts. If no improvement then I'll have to try to troubleshoot a bit more. I was just curious if anyone has had similar problems or has any idea if running this way would cause the previously noted problems.
 
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Cochip

New Member
Nov 29, 2010
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Caldwell, Idaho
So I got the call from the exhaust shop and the go the exhaust all mated up and flowin' nice. However it sounds like the problems persist. So I appeal to you all who know these engines better then I do. Where to start, here? If you haven't read through that huge first posting of mine the issue is the engine will start without issue, but will not stay running long. The initial idle is up a bit like one would expect, but that idle drops quickly and is replaced with a loping/galloping idle that doesn't respond will to throttle. It will die everytime I give it gas while idling the way I described above. I hoped that the open exhaust was the culprit, but it seems that may not have been the problem. Thanks ahead of time for your help.
 
C

Cochip

New Member
Nov 29, 2010
31
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0
Caldwell, Idaho
RazoE;1653020 said:
could be the throttle position sensor, or the idle air control...

do you have the MAF hooked up as well? It's easy to forget to plug it in..
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My hope is that because the engine was a runner without issue when it was removed from the donor car that nothing has changed there. I'm gonna check into those anyway just to make sure. MAF is hooked up and I'm gonna take a look at the air intake in total to make sure I tightened down all the clamps and there is no leaks there causing a poor air/fuel mix. I found a thread on another site where someone was having the same problem and it led him to a fuel pump issue. I was worried about that part of the wiring with this swap and I thought I had it right because how well it starts, but the way it dies makes me think that the pump isn't keeping pressure. I need to check the fuel pressure to see if it drops and causes this issue. Where is the best place to tap into the fuel supply to get a gauge attached and watch the fuel pressure?
 
C

Cochip

New Member
Nov 29, 2010
31
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0
Caldwell, Idaho
Okay so I rented a fuel pressure tester and hooked it up at the cold start injector per the TSRM. With the key in the "on" position I get no pressure what-so-ever. When I turn the engine over I get a good build up to about 40psi and the engine will turn over. I watched the gauge and it'll immediately start steadily dropping pressure and once it hits zero the engine dies. My hunch was right I'm not keeping pressure, but I'll get enough to get it to start. Any ideas on why?
 
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AJ'S 88NA

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Jul 26, 2007
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Should pressure up with the key on. I guess that you have a leak somewhere or maybe the pump is going bad.

Maybe post in the general section you'd get more response and maybe somebody can help.
 
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