Throttle locking at wide open

[slo_5_0]

I've encountered a very odd problem. Driving along, depress throttle to the floor, engine reaches roughly 4000 RPM and suddenly goes flat as though the battery was unhooked. BUT, the throttle is stuck wide open and the engine continues to run as the car coasts with no throttle control. This happened 3 times, the first time I shut the ignition off and as soon as I did the throttle released. The second time I realized the engine didn't wind up with the open throttle so I let it slow down, the throttle released on its own and I continued driving. The 3rd time I was able to data log the event, but I can't tell what's happened. There are two springs on the throttle body with enough tension to make it difficult to open the throttle with my finger and there is not even the slightest big of drag open or close so it's not mechanically stuck.

The TPS sensor is a Ford and seems to work properly - except for this. Is it possible that the TPS can lock itself? A bad connection maybe? I had a problem with it coming loose right after the initial install, but I carefully reconnected with push in connectors and have no other issues with it.

Attached is a screen shot of what happened.

Any thoughts or places to look? What other information could help figure this out?

Pete

[Mike_Robert]

It certainly looks to me like a TPS signal failure, probably somewhere in your cabling or connector(s). Don't overlook the DB37 connections.

[devastator]

So, wait a minute. Are you saying your throttle plate was physically stuck in place? Then when you cycled the power it released? I've never heard of a TPS sensor, or any other sensor, literally, holding the throttle shaft assembly open. This sounds kinda scary. Are you sure about this?

[Mike_Robert]

There are two springs on the throttle body with enough tension to make it difficult to open the throttle with my finger and there is not even the slightest big of drag open or close so it's not mechanically stuck.

I thought the same thing - d'oh!?!?!?? But I'm pretty sure after examining the log that he's referring to the TPS sensor reporting a closed throttle. I wish he'd let us know what happened....

-Mike

d'oh == Whiskey Tango Foxtrot; the forum filter got me....

[slo_5_0]

Thank you for the follow ups. I appreciate the reponse. Sorry for the delay replying back.

Yes the throttle is sticking wide open and the TPS says it is open too. If you take a look at the snap of my log the TPS is 99 and doesn't release until the RPM is dropped below about 1500. The throttle cable does not release. I lift my foot from the pedal and it stays down. There are two springs on the butterfly. It's actually a lot of pressure to open the throttle when operating normally.

I don't see how its possible the TPS could be causing this. Any one have any thoughts about that being possible?

I've tried prying and twisting on the throttle to see if there is any hang or friction. It seems very normal. There are no other interferences in the area that I can tell. The throttle body is new as is the TPS. I just can't see any mechanical reason for this sticking. But I just can't believe it's something electrical either so I wanted ask if anyone could believe this to be possible.

Pete

[FixItAgainTony]

Here is a long shot - how are the motor mounts?
I had a '69 Chevy Impala 350 go full throttle on me because the engine rotated a little, pulled on the throttle cable, which caused it to rotate and pull a little more. It does not sound exactly like your problem, but perhaps something of that sort is causing the accelerator linkage to seize up.

- Charles.

[Mike_Robert]

Pete, according to that log shot, your throttle plate shows very strong evidence of being mechanically shut - the MAP signal is 22 and RPM is decreasing when the TPS is indicating full open. That's inconsistent with a full open throttle plate - it looks exactly like a coastdown against a closed throttle with the TPS malfunctioning. Does this happen often enough to where you could just completely shut down and visually inspect things? Please keep us posted - this is definitely a strange one.

[Joe]

Long shot #2-

Check your body grounds! Sometimes a bad body ground can do this. Your body systems will ground through the throttle cable.

When the cable gets hot it sticks. Turn on the heater, throttle sticks. Volt drop batt neg to the body with multiple body systems on, heater, lights etc....

Again, long shot but I have seen it before.

Joe-

[devastator]

A TPS sensor is a potentiometer or variable resistor. They don't have the ability to become electromagnets. Your problem is elsewhere. Can you test shot in the dark #2 by turning on MS and not starting the engine, then checking to see if the throttle cable is getting hot enough to cause problems? I've had a similar experience to shot in the dark #1. Be sure your cable is not too close to anything that engine torque would affect.

[h22]

I have to go with the bad ground here, unless somehow you have physicly mounted the tps wrong, witch does not explain the low MAP value, a binding or grounding throug the throtle cable makes the most sence, givven the fact that everything shut off. i would double chech the chasis ground to the engine or run another one just to be safe, and go get a replacement cable A.S.A.P!

[slo_5_0]

Thaks for the additional replies.

I've added a 6 gauge ground from the body to the engine in addition to several smaller ones that already existed and the one from the battery. Since the most likely scenario seems to be a binding cable, I rerouted it slightly and to soften the bends that were there. I can't tell any difference. Also, I repositioned the throttle spring so now it's really hard to press the pedal.

Assuming there are two problems here and potentially I solved the cable problem, the one thing that still doesn't make sense, if the cable was stuck, and the throttle plate also stuck wide open, what would cause the engine to just go flat? In other words, you'd expect the engine to speed up if the throttle was stuck open. Or if the throttle plate wasn't really stuck open, in other words it was closed but the logged showed the MS believed it was open, the engine didn't decel like it would if I just lifted the pedal. It sort of soft landed to around 1500 when the pedal freed and I could control the throttle again. I have the AFR high around 17 at that MAP & RPM, so it wasn't getting enough gas to run right, but it wasn't popping. It just sort of coasted like when you shut the engine off while in gear. More like the spark was cut.

I'm using the EEC-IV adapter and wasn't grounding the MS as I assumed this was grounded through the wiring harness. I've now placed a ground from MS to the body. If this should have been done from the beginning, I'll try driving it again and see what happens now that it's grounded. If that isn't required, any other thoughts on things I should be looking at?

One more variable that I have removed, I had an MSD digital LED shift light connected to the spout inside the EEC-IV adapter board with the power and ground also connected inside the EEC-IV adapter to the 12v source and ground. I've disconnected it for now. Is there any likely hood that the shift light could have caused an a problem - pulling too much signal from the spout? The light was set at 4650 RPM and I wasn't reving it quite that high. Can the shift light cause problems when connected to the spout signal?

Pete

Pete

[h22]

Ok, here is another scenario, let us assume that because your datalog showed 20mpa, that the TV was closed. A bad ground on your sensor return would cause the TPS to read full open, it also would most likely cause MS to shut down. When i first installed my Dads unit with the relay box i forgot to run the separate sensor return to the relay box and surprise it wouldnt work! double check your sensor return wire.

This still does not explaun why your throttle peatle was stuck to the floor, but if it was [b][i]just[b][i] a sticking throttle you would have had a runnaway engine!




Joe

[Mike_Robert]

Joe, a railed TPS input on a running engine won't shut down MS. However in a powered but non-running state a full open TPS signal wil usually cause a flood clear situation where the injectors inject nothing. It'll work just fine with no TPS signal at all - I've run without a TPS for some years using MAPdot as the AE trigger.

[Joe]

Initially I was under the impression the issue was the throttle was mechanically sticking for no apparent reason.
(pedal stuck to the floor)

My comment was mainly to make sure the body systems are not grounding through the throttle cable to the block.

I've seen a few conversions where the body grounds were left off causing this issue.

This does not seem to be the case here so disregard long shot #2- Does not seem to make sense to me really with 20kpa and pedal stuck to the floor.

Running without TPS- agreed. Actually works well.

Just a thought about the ground issue-

Joe

Edit- Just fiqured out there are multiple Joe's in this thread- DOH

[h22]

Joe, this is Joe , I actually agree with you about the grounding through the throttle cable, and i also agree that [b][i]just[/i][/b] a railed TPS will not cause a stut down, however a bad signal return can, its happened to me. mine was because i tied the HEI module ground to the return ground, hence no tach. I am led to belive by another person who reveiwed the datalog that map was 20kpa ( map is internally grounded ) , so this leads me to belive that the throttle plate was closed and it shut down for other reasons. as a
i said, still does not explain the petle being on the floor, if you read my earlier post i think your explination makes the most sence. the only other explinatoin i can come up with is a physical issue inside the TPS, that simaltaineously puts it in a bind where it wont release the throttle plate and full grounds the Vref, kicking in the varistor. cordualy, the other Joe

[h22]

Did i see your log right? to me it looks like your map drops way down your injectors shut off, could you acually post the log file and is there a way to add a comment as to exactly when it shut down?

[slo_5_0]

Sorry for the lack of follow up, especially to those that have followed up with me and the topic. I've been unable to get back to the car after making a handful of changes, but I'm convinced there were two problems 1. the throttle cable must have been binding at high load in 1st gear due to engine movement. I moved the cable routing a little and have not been able to repeat the throttle sticking problem. 2. Something else is wrong with either the megaquirt, the eec adapter or wiring in the car.

This is where I could use some additional advice.

I believe it was a coincidence with the throttle sticking and the car going flat because the car still will go flat at various times. I have a log of it posted from today where you can see on the log many of the values jump to impossible numbers MAPdot of 12,000+ or TP of 1,600, RPM of 47,000. I had 1 reset during the log today which was about 10 minutes of driving.

I'm unsure where to start to look for the problem, but the car idles and runs fine except for these periods where the car will pop suddenly or just loose power, but not die. Most of the time this happens under a little or even moderate accelleration, but if you look at the log, it's jumping around at idle. It is noticiable at idle and it's noticeable at cruise. Until today, the values logged were not jumping to extremes as they are now.

No similar problem on the stimulator, so it appears only while on the car.

Can anyone provide ideas to start with troubleshooting?

Here's more spec's on the car - 400+ CI with Vortech running about 7lbs of boost, TFS ported R heads, Super Victor intake with 96# injectors, long tubes, C4 trans with 3,500 stall, car is about 3800 lbs with me in it. Also, running MS code version 2.6

Thanks in advance

Pete

[h22]

Are you running high or low impreadance injectors?

[slo_5_0]

low impedence

[h22]

Check out the threads dealing with MSII and low impeadance injectors, or Goto Diy auto tune and check out the Megemeat 2008.
Basicly the V3 board and MSII has problems with the flyback circuit on [b][i]some[/i][/b] aplications using low impeanance injectors, there are a cfew recomended repairs, the most common one seems to be running a separate wire for the V12 side of the flyback directly to the injector 12v supply. You have to cut the large 12v trace to separate the flyback 12 from the 12v suply to the rest of the board. see here : http://www.DIYAutoTune.com/videos/megas ... enoise.mov



Also double check your PWM settings, just in case.