- This topic has 14 replies, 8 voices, and was last updated 13 years, 3 months ago by
.
-
Topic
-
First of, hello all i’m brand new to the forum and glad to be here.
I could realy use some help here folks. I’m stumped. I have a 1995 Lumina APV with a 3.1l TBI 130k mi…………………….Stoped laughing yet? Anyway the problem is it starts fine and runs all day with no issues as long as you dont shut it down then start it again. That is shut it down for more than 20 min. If you do shut down for 20 min then come back to it. It will start run very rough then die. it will repete this for about 5 min or so then smooth out and be ok again. I can cure this problem by removing the vacume line to the MAP sensor stat the car let it idle for 30-40 sec. then reconnect the MAP and all is good.
Here is what I have replaced.
MAP 3 times
CTS
Plugs whires cap roter
TPS
IAC
Fuel pressure reg.
I have fuel pressure of 13psi even wen car is acting up.
Any thoughts? I would sure love to here some ideas. Thank you so much all.
-
Replies
-
13 psi isn’t terrible for a TBI system, but I didn’t think the 95 3.1 would’ve run throttle body. That’s news to me.
Hi there and welcome to the forums!
Ill start with a few questions –
Is the check engine light on? When using your fuel pressure gauge, does it hold pressure? Any visable signs of vacuum leaks?
Usually when your remove vacuum from a MAP sensor, the PCM will richen the fuel ratio.
Why did you replace those parts already? Did you test them and use logic and evidence as to why they needed to be replaced?
The next time the vehicle has issues, i would do a KOEO test with the fuel pressure guage and see if you dont have a leaking injector. I would also check for spark on all 6 cylinders. Another check would also be to ohm out the ECT and see if the resistance increases or decreases depending on what type of ECT you have as the vehicle is running.
It also wouldnt hurt to check for a 5vREF at the MAP along with your ground and test the MAP sensor with a DVOM and vacuum gauge.
Hope this helps.
is there a check engine light on? you can access codes on GM vehicles pre-96 by using a paper clip on the data link connector located under the dash.
usually they are two adjacent corner terminals and set the key to the on position. Count flashes for the codes, just google some directions for GM OBD I or something.
your fuel pressure seems low in my opinion, you might check out some specs on pressure and volume output for the fuel pump from a parts store just to be sure and consider doing a volume check as well by simply releasing the fuel from a pressure gauge into a container for maybe 30 seconds or less and see what you get.
I hope this helps, I could be completely wrong.
Have fun!Hi scottie35,
Interesting conditions. Based on dreamer2355’s comments regarding the MAP, it almost sounds like some vacuum lines could be compromised. If you have access to a vacuum gauge, check to see that you have at least a steady 18 inches Hg for vacuum while your car is running at idle. Also, given the age of the car, an inspection of all the vacuum lines for cracks and dry-rot would be also be good to do.
I am very interested to hear the outcome on this. Keep us posted.
I baught the car a few mounths ago. some of the parts needed to be replaced i.e, had a wire burn through so I did plugs and stuff. Others I replaced because I am shotguning this problem. So I went to pull and pay I grabbed a few things. No engine lights on. I have had two readings with the FP. I dont own a gage so i have to rent one if i want to test it. The first one I rented was a bit old and worn it showed 13psi steady. The last one i got (I didnt trust the first) shows 13psi but does drop to 10psi and bounce a bit but not below 10. It does not hold pressure after a turn off the car. No vacum leaks. I did check the MAP 5v that checked out and changed voltage when vacum applied. Also checked EGR. What would the symptom be of leaking injector with a KOEO test? I dont get any pressure until i crank engine. The pump doesn’t come on in KOEO. I kind of ruled out leaking injector due to disconecting MAP thus adding fuel fixes it.
You need to also check fuel flow along with psi. Also have any access to a scanner with live data? (Not just a code reader)
I have seen a video on realfixesrealfast , Eric has a link to that web site. Well he shows a car that had a problem with the map sensor vacuum hose. It was so old that when looking at it with the engine off looked fine but when you start the engine it would collapse, see if yours is soft. http://www.youtube.com/watch?v=SfSq5GaTIrQ I hope this link works.
[quote]Quoted From Tri9SS:
I have seen a video on realfixesrealfast , Eric has a link to that web site. Well he shows a car that had a problem with the map sensor vacuum hose. It was so old that when looking at it with the engine off looked fine but when you start the engine it would collapse, see if yours is soft. http://www.youtube.com/watch?v=SfSq5GaTIrQ
X2
WOW, lots of replys and good ideas. COOL,Thanks. I dont have a scanner. I checked the vacum line to MAP its good.
Check pcv valve and hose but make sure engine ground is good and test to see if you have an intake manifold leak.
Well the good people of the forum have already covered the ‘stop replacing parts’ so I’ll skip that. Given that you don’t have a check engine light on I would be looking for someting basic, like many of the others that have responded I think fuel pressure is the first place to start as it does sound like it might be ‘loading up’ on you after you shut it off. 13psi sounds bogus to me however as most fuel injected systems need at least 35psi to run so you might want to track down a better gauge. I like the KOEO test, when you get a good gauge hook it up and let the engine get warm, shut it off and observe the reading, if it starts to drop by a significant amount then that might indicate a leaking injector which is kind of what I’m thinking, gather the evidence to support this however. You might also consider doing a power balance test as this would also show a weak cylinder which could nail down a bad injector. Here is a link to my video on the subject.
http://www.youtube.com/watch?v=bAOmUjAjNjE
Good luck
Awesome ideas guys I do appreciate every one of them.
Let me please clear up a thing or two. About throwing parts at the car. The total cost of parts is about 15.00 Remember this is a 1995 that means I cant rent a scan tool to look at it. It would need to be 96 or newer. Yes I am able to put a VOM on most of the parts witch i did. But I have had in the past found that just because something ohms good doesn’t mean it’s good. So for a few bucks and about 40 min I will change them and look for a change. I don’t want to spend hundreds of dollars on a scan tool that I will only use one or two times.
As for the FP we may be on to something here. A few things to remember is this is a TBI witch is basically a carburetor with two injectors sitting on top of it. 13 psi is in spec for this set up. I THINK. At least that is what I have read. If you know different pleas chime in. As far an the pressure drop with the car off. It has a mechanical spring diaphragm pressure regulator. Is it abnormal for this to release pressure when car is off? It releases the pressure pretty quick when I shut off the car. And remember this problem only happens when the car gets warm then sits for 20 min to an hour. In other words I can stop for gas with no problems. But if i go into a store I have an issue. Thought being a leaking injector would be the other way around? Also I can drive hundreds of miles with no problems. And get about 23 mpg highway. GM only rated car at 24 highway. So doesn’t appear I’m getting bad mpg.
You all are truly a great resource. Even if i never get this solved it’s great to be able to share my frustration. Chears!Most vehicles will hold steady fuel pressure with KOEO for at least 5 mins before it starts to slowly drop.
You could ohm out the injectors and check for shorted windings. The TBI injectors are usually low impedance injectors so look for readings around 5 to 6k ohms. using Noid lights will also show if you have any short to grounds in the injector wiring causing one injector to constantly be ‘on’.
IF the pressure drops right away, that could be caused by a faulty check valve in the fuel pump.
I would do some more research on the specs for fuel pressure and go from there.
Good Luck and keep us posted!
Wife has car at work. So i cant do any test on it just now. But remember. I can fix this problem by disconnecting vacume line to MAP sensor. So i am telling the car it has no vacume at the MAP. Sending the ECU into some sort of default, what that is i dont know. it does not help to create a vacume leak anywhere else. or to diconect the electric connection to the MAP also does not help.
- You must be logged in to reply to this topic.