Im still fighting a starting problem that I posted about a while back, but can't figure out. I want to try to out rule as many problem sources as possible, and thus was wondering if for test purposes I can unplug the knock sensor? Will it run like that, or do I have to do something with the open ends?

Thanks for any help!


Ken

 

It will run like that, but thats not your starting problem unless its hooked up to 24volts or something stupid like that. If you really feel like testing it with it disconnected, go ahead.

 

Thanks madmax!

I just came back from working on the car. I pulled the plugs and cleaned them - even though they weren't really bad, it still starts easier, and runs on all cylinders. I also re-gap'ed the plugs, so that might be a reason as well.

Now, I also decided to check the TPS, and it turns out I am not at all able to reach 4.0V at WOT as per the Tech Article on here. The max I could adjust it to was 3.78V, and then the idle voltage was all the way up at 1.13V. Does that mean that the TPS is faulty, and if so - could that give starting problems and problems idling when cold?

Thanks a lot!


Ken

 

Ken,

Reset the TPS to deliver 0.54VDC in the idle position, and make sure the reference voltage at the sensor is 5.0VDC across the A and C terminals. If the reference voltage is low, you'll never achieve the desired WOT voltage threshold. A low voltage could indicate a connection problem and the TPS, engine harness, or ECM connections. The ECM connections can often be improved by simply unplugging and reconnecting the edge connectors several times. The wiping action of the individual connectors helps clean and polish the card edge traces and connector contacts, and can frequently resolve some of these nuisance problems.

Personally, I suspect that in at least a percentage of cases, people that replace suspected faulty ECMs are actually solving the root problems by this action of removing and unplugging the circuit connectors, and thus cleaning them for better contact. Some of the signals used by the ECM are extremely low-level, and a very little resistance created by a poor connection can alter these crucial signals to a point of failure. The oxygen sensor, for example, only has an effective range of about 700mV, and the CTS circuit is very sensitive to even the slightest resistance change. For the same reasons it is very important to have clean, solid ground connections at the ECM, battery, and engine. Only ¼ volt drop can cause a catastrophic signal change from the perspective of the ECM, regardless of the cause of the signal loss.

 

Thanks Vader,

I did check the voltage over the A - C terminals and they were right at 5V, or 5.02V something like that.
I also did unplug the connector and plug it back in, but only once though.
I also did set the TPS to 0.54V at idle, but then the WOT voltage was barely over 3V, I think 3.08V or 3.12V.

I will try to reconnect the TPS plug several times to see if I get a different result - but if not, what would be a natural next step?
Also, what kind of problems should I see with the low voltage?

I have also recently had problems with code 43, even after replacing both the timing unit as well as the alternator.

Thanks a whole lot, I really wish I could figure this one out because the car is almost undrivable and my wife doesn't dare drive it at its current condition.

Ken

 

Ken- your TPS may be bad but the adjustment on the old 86 TPIs had a lot of slop in it. Getting both idle and WOT voltages both in spec at the same time took a bit of fiddling back and forth. First off, just manually push the TPS all the way to the end of it's range with you finger and see if you can get it over 4.5V. If not, it's bad and you should replace it. If you can then play with the adjustment some more.

As for disconnecting the Knock Sensor you need to run the wire through a 3900 Ohm resistor and then on to ground to bypass the knock senor. Just unplugging it will resut in a check engine light and the engine running like crap due to being in "limp home" mode.

 

Thanks a lot Damon!

I did move the TPS to all possible positions last night, and 3.78V was the absolute maximum I could get it to. So, Im assuming that is shot?
Is the TPS in any way related to the timing unit? I keep getting the code 43 for low voltage at the spark timing unit.

Just as an update on the result from last nights plug cleaning - the car will now run alright on all cylinders even when cold, when the rpm's pass about 2000-2200.
But, there is still no way the car will idle when cold. It needs a minimum of 1500 rpms to run. When coming below that it sounds like it is running at no more than 7 cylinders, but I think even just 6, as it is very unstabile. It will also come with loud "pops" in the headers/y-pipe/cat area. I assume this is from unburned fuel.

One thing that I have noticed, but can't confirm if it is consistent, is that when it gets real cold (15-25°F) the car seems to start a lot easier. But the problem seems to always be there when the temp is above that.

One last thing that might be helpful, when cranking the car, it will start or try to start immediately - but you have to "catch it" and bring the rpms up as described above. IF I don't get it running at that first try, or that the rpm drops so it stops on me - it is very hard to start. I have to crank forever and keep the gas in, and it will eventually catch on.


I am sorry for the long post and all the questions, but this is really becoming a problem that I can't rely on this car. It is the only car we have, and it used to start once you touched the key.

:/
Ken

 

I remember reading a lonnnnng time ago in Hot Rod Magazine's "tech Q&A" (in the back) that if you got water on your TPS, it would hurt the TPS, and cause a rough idle.

Couldn't you measure resistance of the TPS (unhooked from the car)? I don't have my GM book in front of me, but A to C should be a constant resistance. B should be the "wiper" along the TPS, and would vary from zero resistance to full resistance. I'd say measure A to C & write it down. Then measure between A & B, and measure resistance from closed throttle to WOT. The meter should go from 0 resistance to high resistance, or vise-versa. (B & C would show the opposite).

Also, you could use an analog meter to verify that the sweep from 0 to full resistance is smooth, and not jerky.

Have you checked fuel pressure? When my last pump died, I had to rev the engine pretty damn high to keep it running. (Of course, the pump broke at Englishtown Raceway Park, just as I was lining up to the tree- how embarassing!) That was NOT a fun ride home!

 

Thanks Tom!

I will check the the TPS resistance as you suggest. I know the analog meter would be more accurate but at least with my digital meter the increase was steady, but just didn't go above the 3.78V

Regarding the fuel pressure - no, I haven't checked it, but I will do so. Actually, Im a little worried about my injectors, if they can be bad or dirty.
When your fuel pump went bad, did the temp on the engine make any difference then? I would guess not?
My car is only having these problems when cold. When reaching normal operating temp, it will idle.


Thanks again for you guys help!!


Ken

 

Just wanted to come with some additional information regarding my problem that I have just become aware of - incase it rings a bell for anyone.

I have found that when the engine is cold and the rough running/misfiring is going on, the brakes are consistantly a lot "worse" than when it runs fine (at normal operating temp). The transmission also shifts VERY hard when it is cold, and it also shift at higher RPMs than usual. This also recovers once the car is warm. The only thing that I can think of that relates the three (running rough, bad brakes, rough shifting) is vaccuum??

EDIT: I forgot to mention that these last few days I have also experienced a lot of Code 43 and 44, if that can be any pointers


Any ideas are VERY welcome!

Thanks a lot,


Ken

 

Ken, did you reset the TV cable adjustment? That may help with the shifting...but the 700R4 is not controlled via a vacuum modulator like the TH350/400's are.

Could be a vacuum leak...hint may be in the loss of the brakes 9assuming it's form the power brake system causing the problem).

Have you put a vacuum gauge on it to see what's up?

Also, doing the knock sensor bypass could help you in figuring out your problem for the 42/43 issue.

 

Thanks Mike!

I have not touched the TV cable, and Im kinda reluctant as the trans shifts perfectly fine once the engine gets warm.
I sure didn't know the TH700's didn't use vaccuum. There is a small vaccuum hose that goes from behind the brake booster and across the firewall to the pass. side and into a bundle of wires that goes down on the pass side of the engine. I just assumed that went to the trans. Do you know what that is?

I have not put on a vaccuum gauge, to tell you the truth - I don't know how I would use it, nor where to get one. Would a place like AutoZone have it? Also, where do I hook it up?

I will get a resistor for the knock sensor tomorrow to see if that brings me anywhere.


Thanks lot for the help so far!


Ken

 

The vacuum hose you are referring to should go into the car for the AC/heater controls and stuff.

Is this a MAF car?

 

madmax,

Yes, it is an 86 305TPI.
Okay, so that is the one for the HVAC, I never knew exactly where it went.

Thanks,

Ken

 

Try, just for the sake of testing, unplugging your MAF and starting the car. Sometimes a MAF going bad will cause problems immediately after the engine fires up. Not usually like you are expereincing but similar.

The power brakes I wouldn't worry about. When an engine is stumbling around it isn't making much manfold vacuum and the assist from the power brake booster will be less- hard brake pedal results.

Ditto the tranny. You're opeining the throttle more to keep the motor running which will increase the shift point RPM and shift the tranny harder.

Fix the first problem and the others will likely fix themselves.

 

I dont know if you did it, but verify the TPS is working right. If its jumping around when you slowly open the throttle, its no good. Sounds like a vacuum leak though, MAF cars do not like vacuum leaks at all. Only thing I wonder about is why its not setting a code for the MAF if there is a leak, usually when its so bad that the car isnt running right, it will set a code.

 

Thanks guys,

Damon, I did unplug the MAF as you suggested (I think at CZ.C) but that only made it worse - so I don't know if that would be related. I could barely make it run then.
I see what you're saying with the brakes/tranny, that does make sense.
And you bet I'd fix the problem if I could only find it.

madmax, as stated in one of the posts above, I checked the TPS, but even though it is not jumping around, Im not able to get a decent range on it. When setting it to 0.54V while closed, I will only be able to get around 3.2V for WOT. When I tried to adjust it to get the maximum out at WOT, I still could not by any means get over 3.78V. So, I have a new TPS on order. Should be in shortly.


Today the car has a particularily bad day. It would run on 6(?) cylinders first, when it got somwhat warm I could feel that a 7th started working, and right before I came back home and the car was around 200°F, I felt that it was about to start running right.
When that happens it will kinda give small "backfires" in the exhaust and they get more and more frequent until it all of a sudden just starts running right.

What about the code 43/44, what are common causes of those?

I did mention in a post a while back when I first started having problems, that all the engine mods in the sig. was done at the same time, and that I've never been able to get it to run quite right after that. I do still have the stock chip, could that be a problem?
Also, is there anyway this can be related to the injectors? Can they in any way have problems that depend on the temperature?
And last question - I understand that a faulty fuel relay is fairly common on our cars, what are the characteristics of that problem?

Thanks again folks!!

Ken