Starts Fine and Stalls

[USArmyCombatMedic]

Hi all, I am new to this forum so please bear with me. I have an 87 Chevy R10 with a 350 and 700R4; 80,000 miles.

I have no idea what the problem could be hoping you guys can help. I bought this truck about a year ago. At that time it ran great but it would die at idle if it sat there for a while such as at a stop light. The truck would also shift hard into first and reverse, sometimes causing it to stall itself. That's when I gave up and left for a years worth of training for the Army. Now Im back and trying to attack this at a different angle.

I tore the truck apart and have rebuilt it from the ground up, completely new suspension (8 inch lift) system, brake system, steering system, frame is all painted, rebuilt transmission, rebuilt torque converter. I tore the truck apart figuring the stalling was caused by a faulty converter, lo and behold I put it all back together and same problem. Shifting is great in everything but P to D and P to R. Truck still stalls if I do not give it gas such as a stoplight.

What problems could this leave? Fuel, Air, and Spark correct? Took it in for a tune up, new plugs, wires, distributor cap, rotor, timing was redone. The problem persisted, mechanic said get a new distributor assembly. Have not got it yet since they are a bit spendy. New starter.

The air category is a bit mysterious. I went through and researched this. It all seems to be correct, no vacuum leaks that I have found. If I disconnect the intake manifold vacuum line from the cruise control vacuum line it produces good vacuum and will run for a minute or so (really low idle) and die. If I hook the two vacuum lines up it will start and die within a few seconds. What is up with this?

Then there is the fuel category. New tank, new lines, new filter, rebuilt TBI, the only thing this could possibly be is fuel pump correct? Since the injectors work great and spray a cone pattern like they are suppose to.

Like I said I have researched this a lot. People say disconnect the torque converter switch to make sure you did not screw up installation- no difference. Check EGR valve- stalls when compressed. Check coolant temp sens.- removed no difference. New IAC- no difference. New TPS- No difference. It will not throw me any codes other than the 12 I am suppose to have.

I am really stuck here, I have a lot of time and money into this and don't want to continue if it will be a problem truck the rest of its life. Any help will be greatly appreciated, I am only 20 so bear with me on vehicle knowledge please. The only potential fixes I can see here is new fuel pump? new distributor? recheck vacuum lines? None of these seem to make good sense to replace though. Thanks in advance.

[clapage6]

I would check for a leaky injector for sure..

and/or float level carb'd?

had the similar issue when i was running a holley, incorrect float setting not shutting fuel delivery downa nd causing fuel to dribble in over the ventruis.. I could see it with the air cleaner off

[USArmyCombatMedic]

Thanks for the quick reply! How would I check for a leaky injector? It seems to have a good cone spray pattern and both injectors seem pretty even. I think I will end up testing the fuel line pressure because that would rule out a failing fuel pump correct? I hear the pressure test is difficult on these trucks due to no point to connect the gauge.

Also what did you mean by float level carb'd? This truck is throttle body injected. Although if I cant figure out this stalling problem I am going to switch It to a carb to rule out fuel and air problems.

[clapage6]

Originally Posted by USArmyCombatMedic

Thanks for the quick reply! How would I check for a leaky injector? It seems to have a good cone spray pattern and both injectors seem pretty even. I think I will end up testing the fuel line pressure because that would rule out a failing fuel pump correct? I hear the pressure test is difficult on these trucks due to no point to connect the gauge.

Also what did you mean by float level carb'd? This truck is throttle body injected. Although if I cant figure out this stalling problem I am going to switch It to a carb to rule out fuel and air problems.

gotchya my carb statement was just if it was carbureted or not, i didn't think it was but just wanted to be thorough :-p

so yeah my first thought is to check your plugs and exhaust for raw fuel, that would be a pretty decent indication you're way rich and would re-affirm the leaking injector.

however a fuel pressure check would need to be done to affirm a lazy pump idea. but i would be the least likely to cause only idle problems..

oops also noticed, have you tested your map sensor as well?

[USArmyCombatMedic]

I do not believe so. How would I go about checking the MAP and where is it found? Im assuming its in the cluster of sensors on the passenger side of the TB? Also any idea why when the vacuum is hooked up it works less than when it is not hooked up?

[clapage6]

yep, the map sensor is a black rectangle shaped sensor that should have i believe a 3pin or maybe even 5pin plug into it and a vac line as well

oh and with the vac lines unplugged i think you should not worry about just yet.....i THINK ha..

try unplugging said map sensor and see what happens, should idle decent but sometimes it wont matter and will still need to be tested, there should be a bunch of write ups online to test it... in my only experience with it, it idled with it unplugged and would die when plugged-in so I replaced it.

[USArmyCombatMedic]

Ok I just researched how to do the MAP sensor test. I will do that this weekend. Also would it hurt to temporarily block off the EGR to see if that helped? Seems like that's a common problem?

[Sodell]

TPS usually causes this. You replaced it so that may be out. How does it run when you start it cold? Does it run well with a higher idle until warm? There is a coolant temp sensor ear the thermostat housing, I see you disconnected it but this is what tells the computer what temp the engine is at ect, this causes similar issues when bad and if bad would not make any difference, this part is relatively cheap. I would also check the pressure regulator.

[USArmyCombatMedic]

I have heard that a lot of sensors are bad right out of the box. I checked the TPS with a multimeter and it seems to be working correctly. It runs rough at idle cold. If I give it just a little gas for a minute or two until it warms up it still idles rough but it wont stall. The coolant temp sensor is like $10 so I think I will just buy one like you suggested.

As far as the fuel pressure regulator, that's the little orange diaphragm with the metal circle inside the TB correct? I think I replaced it when I rebuilt the TB but that was almost a year ago so its highly possible its faulty.

[Sodell]

If it is running rough and stalls out when cold I would start there.

[pontgta]

I would start here...... This is the IAC valve reset procedure.

Posted by RFmaster orginally:

http://67-72chevytrucks.com/vboard/s...d.php?t=515419

1. Install a jumper wire between Pins A & B of ALDL diagnostic connector.
2. Turn on the ignition (but don't start the engine)
3. Wait 30 seconds.
4. Leave ignition on and disconnect the IAC connector (four wire plug).
5. Remove the jumper wire from the ALDL connector.
6. Start the Engine. The engine probably will run rough and may stall. Just restart and try again.
7. Adjust the throttle stop screw to set the idle to 500 RPM +/- 50 RPM. - stock camshaft!
8. Turn the engine off and reconnect the IAC connector.
9. Turn ignition on and adjust TPS to proper settings. (0.60 - 0.65Vdc at idle is typical, but 0.3 to 0.9Vdc will work)
10. Repeat procedure until the 500 RPM +/- 50 RPM (stock cam) in step 7 can be maintained while TPS is at proper idle setting. Performance camshaft may require higher idle RPM!
pontgta is online now Report Post

[wilkin250r]

Still sounds like a vacuum leak to me.

Rebuilt with an 8-inch lift, I wanna see pictures of that beast!!

[USArmyCombatMedic]

Alright it looks like I have my work cut out for me this weekend! Check out the MAP sensor, get a new Engine Coolant Temp sensor, check for vacuum leaks again, reset the IAC and double check TPS, and rip apart my TBI to clean it and check the fuel pressure regulator. A lot of these depend on if I can keep her running that long though!

How hard is it to ballpark 500RPM or should I just pick up a timing light with a tach on it?

Wilkin Ill throw some pics up for you this weekend. I think shes got 8 inch leafs in front, 4 inch leafs in the back with a 4 inch shackle flip. She aint too much of a looker yet since I have done no body or engine work yet but soon as I get her running prime you can bet they will be next on my list.

I apologize for the delay in response and being able to work on it and get back to you guys! I am a full time college student and working two jobs... Thanks again guys!

[Sodell]

Make sure you unhook the battery over night, or a good period of time, before driving it. The ECM has to relearn if you replace a sensor. You can also reset it under the dash. Also make sure you unhook the battery whenever replacing any of the sensors or unhooking anything on a TBI.I would not mess with the throttle screw, only as a last resort.

[USArmyCombatMedic]

Alright, Just got home and threw in a new Engine Coolant Temp Sensor. The truck starts and idles for about 2 to 3 min before dying now. It runs a bit rough (pretty close to normal) but I have a feeling that has something to do with the timing. I had my brother unhook the battery overnight so as to reset the ECM.

As for the MAP sensor. The article I read says to hook a multimeter up to the negative batter cable and middle wire of the MAP. It then says to turn the battery on and it will read 4.7 or there about (mine reads 4.6 which is pretty close). As you blow into the MAP sensor, the voltage is suppose to go down to about 0 (my MAP sensor voltage goes up to above 5). A bad MAP sensor is suppose to stay at 4.7 or 0 volts. Is this a bad sensor or is this some electrical problem? It seems that we could be onto something here...

Im sure this might help in some way or another but I forgot to tell you guys that the truck takes forever to start cold or warm. Im talking like 7 to 8 seconds of cranking. If I hold the pedal at half throttle or pump the gas pedal to half throttle it helps but still takes another 3 to 4 seconds of cranking. Fuel, Ignition, or electrical?

[USArmyCombatMedic]

After working on it for a couple more hours, it has become apparent that I have a HUGE parasitic draw somewhere. The battery is brand new and I am going from 12.7 when running (should be between 13.5 and 14 right?) to 11.85 volts in a matter of 1 to 2 min which causes it to stall. Now bases on my research this is a massive draw, so out I go to start pulling fuses. The alternator appears to be working and I even took it in to O Reillys to double check.

[USArmyCombatMedic]

Alright guys. Sorry for the long delay but as previously stated I have been really busy lately. So I have been doing some work on the truck and have fixed a few things. First of all, the rough idle is fixed. The timing was a bit off and also I messed with the IAC as stated by pontgta. The electrical problem has been fixed as well. Turns out the alternator was hooked up wrong. I rechecked the vacuum lines. I am 98% positive this is not it. I have tried both the propane and carb cleaner test as well as physically expecting every line.
Anyways, the truck still takes a good 10 seconds of cranking to start up. It will run as long as I want it to at idle in park. As soon as I shift it to drive or reverse it will die if I do not constantly give it gas. Again, its a rebuilt tranny and torque converter so it is very unlikely, not impossible, that it is either of these. Thanks in advance

[Jabes1]

Sounds like something within the column. You said it was hard to put into gear... Try bypassing your neutral safety switch and see what that does.

[pontgta]

do you have dual fuel tanks? If not i think it could be either a bad fuel filter(i know its new) or bad fuel pump. If you do check the switching valve. I had a loose hose connection in the tank that caused this problem because of the loss of fuel pressure. I would check fuel pressure. also make sure you have all the connections hooked up correctly.

[USArmyCombatMedic]

pontgta you did it again! I had dual tanks and took the right off because it had a basketball size hole in it. Thanks to MN winters. Anyways, this makes sense, like I said it was hard to start ever since I bought it and due to the hole, and removing the tank without plugging the line, it has never been air tight. I loosely plugged the missing tanks line with bolts, redneck but temporary just wanted to make sure it would work. Starts like a normal vehicle now. I think for the shifts I will mess with the column like jabes1 said, but since everything else is now fine Im thinkin I just need to mess with the TV cable. Thanks so much again for all the help!

[Jabes1]

Awesome.... glad its running! Don't you just love simple inexpensive fixes!?!?

[USArmyCombatMedic]

Cheap easy fixes are definitely the best! Unfortunately the problem is back. It start instantly for 5 or 6 tries than went quickly down hill after that. It now takes 10 sec of cranking to start and if I push pedal in 1/3 way it starts in about half the time. The only thing I did before it started working normally was A change the spark plugs, and B plug the dual tank lines. So my questions are, is it ignition problems because as soon as I put new plugs in it fired right up? Or, is it still probably my fuel pressure, I could make fuel line plugs a little tighter but not much, it might be possible that the extra PSI caused a burst line, but they are all new except for one? Or, is it completely unrelated and the fact that it started normal was a freak accident. Also, if I prime the pump several times, it seems to start a little faster as well.

[pontgta]

I think if you have eliminated the other tank. i would bypass the fuel selector valve. you have 3 lines one fuel supply(large) 1 slightly smaller(return) and the 1/4 which is the vent(not connected to the selector valve(connected to a T and to the other tank. Make sure they are all good. sound to me like its still fuel related.

[USArmyCombatMedic]

I will definitely bypass the selector valve. I think in the future I will go back to dual tanks but as for now, one will do. I installed a digital tach and here is what I came up with, not saying this has anything to do with it. Start number one took about 10 seconds of cranking to start, started at 1100RPMs over 5 min it dropped to about 585RPMs were it instantly stalled. Start number 2 took equally as long, but since the engine was warm started at 700RPMs and fell to about 590RPMs after a few seconds. Then it spiked up to about 640 where it stalled after a about 45 seconds. Again, not sure that has anything to do with it, however I found it odd that it wouldn't idle lower than 585RPMs since 500 is stock. I will get a fuel pressure gauge as soon as I get paid. Would it be better to get a pre TBI, in-line tap and fuel pressure gauge, a fuel pressure gauge that I put in my electronic cluster, or both?