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Am I on the right track?


Trying2Help's Avatar
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07-22-04, 09:29 AM   #1  
Am I on the right track?

1988 Chevy Caprice, 305, VIN code: H

Problem: Poor Idle, Missing or hesitation while driving down the road.

Checked EGR: No vacuum to EGR, replaced vacuum control solenoid.
Still no vacuum being applied to EGR. Jumped solenoid to battery to ensure it is working, can hear it click. There is vacuum at the inlet port of the solenoid, but nothing at the outlet to the EGR.

Signal not coming from ECM to solenoid? Determined that the "signal" is really the ground path for the solenoid, as it does have voltage applied all the time while engine is running.

What determines, when the ECM should apply signal to energize EGR?

Checked MAP sensor: Key on (engine not running) = .5 V
Our altitude is approximately 2500, should be 3.5 to 5.1 V (must be bad)
Just for S & G's apply 10 inches of vacuum to MAP = 2.3 V
15 inches of vacuum = 3.2 V
Voltage going the wrong way! MAP sensor is bad, need to replace. Part is now on order as the parts store didn't have one in stock. Should be here today.

Decided to pull codes, just to see what it says: pulled codes (12 and 41) both of these have to deal with no reference pulse from distributor????? What would cause this?

Check EST: Timing at 2000 RPM with ECM ungrounded = Timing mark moves with the change in RPM.
Timing at 2000 RPM with ECM grounded = Timing mark does not move with change of RPM, but is different than timing of the ungrounded ECM.

I BELIEVE, the EST is working. What else would cause these codes to be set? Could the MAP be my whole problem? Causing the EGR vacuum solenoid not to energize and the codes to be set or is there something else I need to look at?

The car seems to run ok, other than being a bit hard to start, dies at some of the stop lights, hesitates/misses while driving down the road. However, at times it runs fine, others are worst.

Any ideas? I will replace the MAP and continue from there, but wanted to know if there were other things I should look at.

 
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07-22-04, 02:33 PM   #2  
Posted By: Trying2Help The car seems to run ok, other than being a bit hard to start, dies at some of the stop lights, hesitates/misses while driving down the road. However, at times it runs fine, others are worst.
Now, that statement makes a lot of sense!!!!!!

You couldn't be farther off with this stuff
A code 12, I believe means "all OK"
There is no code 41 for 88 Vin H
The EGR isn't supposed to have vacuum at idle. It will only energize at cruise, under load, at operating temp
From what I can make of your MAP testing, it doesn't sound like it has a problem. You have a miss and a hesitation, how about the obvious, the cap, rotor, plugs and wires.
Does the accelerater pump work properly? Is you fuel filter clean? Is you check engine light coming on?
Sounds like your ignoring the basics and diving into obscure possibilities.

 
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07-22-04, 03:13 PM   #3  
Posted By: Desi501 Now, that statement makes a lot of sense!!!!!!
Ok, I will agree that the statement sounds a bit off. However, some of the time it does run fairly well, others it is apparent that there is a problem somewhere.

When I checked the EGR I had it a 2000 RPM's, according to the repair manual that is where you check it. The engine was at normal operating temp.

Posted By: Desi501 From what I can make of your MAP testing, it doesn't sound like it has a problem.
Than 5 V applied and .5 V out is a normal reading, for no vacuum applied? And when you apply vacuum to the MAP the voltage should go up?
Posted By: Desi501 You have a miss and a hesitation, how about the obvious, the cap, rotor, plugs and wires.
Replaced and it ran great afterwards.
Posted By: Desi501 Does the accelerater pump work properly?
Not a problem there
Posted By: Desi501 Is you fuel filter clean?
New
Posted By: Desi501 Is you check engine light coming on?
No

As for the codes: 12 is okay (although the Haynes manual says "No distributor reference pulse" in the data sheet. However, in the testing section, it states, "A Code 12 indicates the system is operating properly and capable of trouble code output."
So what about the code 41, where did it come from? It has to mean something. The Haynes manual says, "No distributor reference pulses to ECM with engine running."

I will go back to the basics and look again, I may have missed something. Been there, done that, just didn't think I would bore you with all the basic things I have already looked at.

 
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07-22-04, 03:25 PM   #4  
I'm getting a little confused here. You say you replaced the ignition parts and it ran great. Do you still have a problem and specifically what is it? I checked codes for that specific year and engine code and the is no code 41 listed. I wouldn't bet the farm on Haynes. They give you very generic stuff sometimes. your not getting a Check engine light so I doubt it's setting a code at all. The worst symptom an EST problem will give you is "pinging". Most EGR's are not programmed to energize in park or neutral. Forget the EGR unless it's loading up at idle and that would only mean it stuck open. Post back with very specific symptoms and exactly when they occur.

 
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07-26-04, 09:22 AM   #5  
41 is probably left in ECM from playing with the timing.
With no code, I'd start back at the basics.

 
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07-28-04, 11:49 AM   #6  
Ok, let's start over, maybe I was on the wrong track.

I replaced the dist. cap and rotor, determined the MAP is working correctly (even if it doesn't match what the Haynes manual says, it is working).

The problem is this and it doesn't happen all the time or every day, so it makes it hard to pin down.

When there is a problem: the car start a little harder than normal, Pull out of driveway and it will die. Start it again (easier this time) drive one block to stop sign and it may or may not die. Once you are on the road (60 mph) you can feel it miss/surge while holding the thottle steady.

Any ideas?

 
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07-28-04, 01:07 PM   #7  
I'm assuming that this is a TBI fuel system. Have you checked the fuel pressure? Additionally have you checked the fuel pressure while you're driving down the road? What happens when you stand on the gas pedal? Your symtoms sound similar to clogged fuel screen in the gas tank.

 
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07-28-04, 02:11 PM   #8  
Check it real good for vacuum leaks also.

 
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08-04-04, 11:47 AM   #9  
Ok, I took a step back and decided, maybe I had assumed to many things. Sooooo we are starting over.

I have replaced the rotor, dist. cap, spark plugs, plug wires and the EGR sensor, fuel filter, air filter, oil filter and oil. I have checked for vacuum leaks, loose wires, anything visual that would jump out at you.

Still have an intermitent problem. It is hard to discribe as it doesn't happen all the time and not under the same condictions. However, let me give it a shot.

Seems to stall and catch when cruiseing at road speeds (40, 50, 60....MPH). However, if I stomp on the gas, it will respond (sometimes with a bit of hesitation).

This is a well maintained car, so has had the maintenance done on schedule, if not early. It does have 140K on the engine. There are no leaks and the engine is clean. When I drain the oil at 3000 miles it is a darker but not totally black and thick like I have seen in other engines. So I am assuming it is clean on the inside as well.

Haven't done a fuel pressure test yet, will have to try that tonight along with a volumn check. Any other ideas?

 
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08-04-04, 03:28 PM   #10  
Posted By: Trying2Help Haven't done a fuel pressure test yet, will have to try that tonight along with a volumn check. Any other ideas?
This needs to be done while your experiencing the problem. You may have to rig something up for a fuel pressure gauge and tape it to the windsheild so you can see what happens to fuel pressure when the problem starts to occur.

 
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08-04-04, 04:08 PM   #11  
Ok, of course this has been part of the problem......can't fix it if it isn't broke!

I will see what I can rig, I am sure the wife will be real happy with whatever I come up with.

 
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08-04-04, 04:42 PM   #12  
one other thing you may check is the vacum to the map sensor, throttle bodys sometimes carbon up that port which will make the map readings sluggish and can cause some of the symproms you are describing you can usually just place your finger over the vacum line to check it for a strong pull or you could install a vacum guage up to the map port and snap the throttle the vacum should quickly drop and bounce right back after throttle is let up.

 
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08-05-04, 08:34 AM   #13  
Thanks, bejay. I will check that. Never thought about it, I did check the sensor, but never check to ensure the vacuum was getting to it....hmmm. Have to pay more attention to the details here.

Thanks again.

 
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