Stumble on Accel - TCC?

smitty286 · Post by **smitty286** » Wed Jun 11, 2008 5:22 pm

Ok Guys,

Having a strange driveability issue with my '94 (Base, 3100/4T60E) that I could use some input on:

When I attempt to accelerate right after putting the car in gear, it stumbles and bucks like it's not getting enough gas, then smooths right out after 10-15 seconds. It starts right up and idles glass-smooth in gear, it isn't until you actually give it gas that it acts up. It doesn't do it when hot, but it doesn't need to sit overnight for the problem to appear either - a couple hours at rest is enough to do it.

I changed the fuel filter (was due anyway) and the TPS (didn't notice any other TPS symptoms, but mine sounded really gritty when operated by hand, figured it was on its way out anyhow and might be a contributing factor), but I don't think the problem is actually engine related - if you take it out of gear while it's acting up, the engine smooths out and surges right up; put it back in gear, and it bucks and stumbles again until those 10-15 seconds are up.

I'm not really a tranny guy, but it almost seems reasonable to me that if the TCC solenoid were sitting partially open at startup and somehow being slowly forced back shut by the increased line pressure of acceleration, that might cause what I'm seeing. At 192k, the tranny actually still seems to be in very good health - shifts properly, no slippage, locks/unlocks like it should on the highway, fluid looks and smells fine, doesn't even leak. This problem is really just a minor annoyance at this point, but I'm worried that I may be putting undue stress on a high-mileage drivetrain and setting myself up for a bigger problem soon.

Anybody run into this before?

SuzukiGhostRider · Post by **SuzukiGhostRider** » Wed Jun 11, 2008 5:48 pm

This sounds like a fuel problem to me. Your engine isn't under load in Neutral or Park. I'm going to say you've got either fuel pump or injector issues. You say it stumbles upon accel. Well, you're asking for quite a bit more fuel upon acceleration than at idle. Test your fuel pressure at the rail. GL.

smitty286 · Post by **smitty286** » Thu Jun 12, 2008 12:47 pm

My first thought was fuel too, but I figured that would cause a more continuous problem...good suggestion though, I'll see if I can scrounge up a pressure tester this weekend. Thanks for the reply!

SuzukiGhostRider · Post by **SuzukiGhostRider** » Fri Jun 13, 2008 3:36 am

NP! Just for shats and giggles, check the condition of your coil packs, and spark plug wires too. If you know how test the coil packs. GL. Let us know and we'll get you sorted.

JeffD · Post by **JeffD** » Fri Jun 13, 2008 5:39 pm

I've had a similar problem ever since I bought my car. My fuel pressure isn't the issue, I have speed density anyway and I think I have a vac leak somewhere. you might want to check that. you also you might want to check the Mass airflow sensor, if the screen has junk on it clean it off, sometimes you have to clean the element too. what ever you do don't bend or damage the honeycomb pattern. CRC, I think, sells a MAF cleaner spray.

JeffD · Post by **JeffD** » Fri Jun 13, 2008 5:42 pm

prolly not TCC. The TC clutch is normally off, so it takes a command to engage it. the tendency is for them to stay on because of debris and stall your car as you come to a stop. When your engine is cold TCC is disabled.

JeffD · Post by **JeffD** » Sun Jun 15, 2008 9:11 pm

any progress? So many people leave the helpers hanging, kinda annoying.

smitty286 · Post by **smitty286** » Mon Jun 16, 2008 10:28 am

Sorry SCB, I appreciate everyone's time here and I surely don't mean to leave anyone hanging - it actually turns out that the buddy with the pressure gauge is out of state for a wedding; he should be back in a couple days, I'll definitely get back with some results once I can get them.

JeffD · Post by **JeffD** » Tue Jun 17, 2008 3:08 pm

I didn't mean that your annoying, just it seems that whenever I let people know no one ever gets back on. so thanks for keeping up.

smitty286 · Post by **smitty286** » Thu Jul 31, 2008 12:30 am

Okay, so I finally got around to the pressure test (been tied up with some MAJOR home repair problems the past few weeks, sorry for just disappearing like that):

41 PSI at the rail with the engine off, down to 36 at idle. My service manual says that both these values are acceptable (on the low side, but still within range); the one problem I DO see, though, is that the pressure drops down to about 32 PSI and bounces around erratically once you get up around half-throttle; not good, but I have a hard time believing this could cause my problem since it goes away so quickly after start-up. I also did a bleed-down test while I had everything hooked up: the 41 PSI bled down to 37 after 10 minutes, 32 after 20 minutes. I then manually relieved the pressure down to 12 PSI and it held solid for 30 minutes before I took the gauge off (this is the bleed-down test that the book calls for, I'm not sure if the failure to hold at higher pressures means anything).

I also got my hands on a scan-tool that does live data and checked the MAP sensor (I believe '95 was the first year for MAF, mine's SD), I think it looks good but I've been having a hard time finding specs to compare to: about 10 in/Hg at idle, up to 16-22 under load depending on how hard I accelerate, responds quickly to throttle and reads the same pressure as the BARO sensor with the engine off (within 0.2 - 0.5 in/Hg). No codes either - I figured such a noticeable stumble should at least set a misfire code, but perhaps these older PCMs aren't as sensitive to misfires as OBDII systems are.

I'm thinking the borderline fuel pump should be replaced while it's still nice outside (it could just be dirty socks, but I'd be crazy not to replace a pump with that many miles while I had the tank down), but I don't hold out much hope that it will solve this problem. Vacuum lines look good on visual inspection, I may try a propane test next to be sure...

Mr. Beefy · Post by **Mr. Beefy** » Thu Jul 31, 2008 11:06 pm

I think it sounds like a weak coil. Test the ohms across the polls and let us know. Should be 7-10K ohms. Anything outside of that replace the coil.....

http://www.autozone.com/shoppin....017e720

Vampcrist · Post by **Vampcrist** » Wed Jul 21, 2010 7:52 pm

So far thats the closest to what I have going on with mine I wish there was a finished post on this one of what caused his problem unless he replaced the MAP and it changed

DTMAce · Post by **DTMAce** » Wed Jul 21, 2010 9:30 pm

Anyone check for a vacuum leak?

Vampcrist · Post by **Vampcrist** » Thu Jul 22, 2010 2:33 am

vacuum is at about 17 on mine and jumps up to 20 something after a rev once it starts to build back up

DTMAce · Post by **DTMAce** » Thu Jul 22, 2010 9:55 am

Yes but yours being older than 94 doesn't use vacuum to operate part of the transmission. Unless you changed it to a 4t60e?

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