Hi all,

I've had some time for the ol` bird as I'm using up some leave time, only to find, she's not running to well. From what I can tell:

On a cold start (car hasn't been run for a good 8-9 hours), she starts just fine.

When the car warms up, it dies. Will not start again. Lots of backfires, very audible from the intake. No codes stored, no SES.

Started off with a basic tune up as it needed one anyway: New plugs, wires, cap and rotor button. Just for kicks, tried to start her up -- and found the coil was dead. A trip to NAPA verified the coil had given up after 21 years of life, back home with a new one. She started, but same thing as before.

Luckily I had remembered to grab a fuel filter and went to work changing it out. After a bath in gasoline, it was changed. She started easier when cold, but same thing, car warms, stalls out.

So I sat down with a beer and the dog and I came up with the idea that if I pluck one of the sensors one at a time -- I could see if its a sensor problem.

1st attempt: MAP sensor: Line was clear, wiring unplugged -- the car started and ran -- when hot! My ASSumption is that the car is using a default table in the computer in case of a failure. I did notice it still tends to backfire (intake audible) when its below 1000rpm, near 500-400rpm when the IAC motor opens to keep the engine running.

I consulted my good friend, Sam Adams, my trusty sidekick: the dog and now you, wise souls of thirdgen.org.

Could it be the fuel pressure regulator? I can't reason this as the engine has more of a demand for fuel when cold. I can rev the engine with the MAP unplugged just fine - no break up or misses.

Could it be the MAP sensor? How would the car start and idle cold just fine, but when warmed, completely dies?

Maybe the fuel pump? Not sure - An engine requires less fuel warm, and as RPM drops -- ariflow drops with it. It would make sense if the car missed or acted funny when giving her the goose.

 

Remember the engine is in open loop on cold start up ignoring sensors. https://www.thirdgen.org/open-loop-closed-loop

Have you checked for leaks/cracks in the map sensor vacuum line? You may want to take the tbi unit off and clean the crap out of it. I found a lot of crud in mine when I modified it and rebuilt it. Especially on the bottom where all the vacuum flows. It is possible the MAP is bad and would explain what happens when not connected. Could be the IAC or crud build up in that area.

 

You may have broken or ruptured in tank fuel line that connects fuel pump to the feed through. If you have original FP the probability is very high. When engine is cold the fuel in the gas tank is cold and rubber hose is not leaking fuel extensively. Once fuel warms up, in tank fuel leak increases starving your engine - causing lean pops.
The easiest way is prove or disprove this is to perform Fuel Pressure check. Stock TBI works at 13 PSI (give a take), but I have seen TBI equipped cars and trucks with symptoms like yours running on only 5-6psi. In all of these cases fuel pump and hose replacement did the trick.

Check fuel pressure - your sensors are probably good.

//RF

 

X2

 

Well Gents,

Thanks for the replies but found fuel pressure to be ok (~13psi), even when warm, and under some load (in drive, on the brakes)

So, I figured I'd try the ICM. When we tested it, it failed 1/3 times. Still no dice.

The strange thing is, the car runs great once its over 1000 RPM, you can punch it and she'll rev up with no problems. However, at idle, you punch it - you get all sorts of pops and visual backfires through the intake. I can't get the car to go into gear without causing a scene to futher test higher RPM (and load) operation.

Decided to pick up a MAP sensor as well - no dice, same thing.

I just ordered a Flaming River timing light as well as a plane jane craftsmen with dial back. I can't wait to try and find the balancer marks.

I've also invested in an ALDL cable to see what I can find with WinALDL...

Might try unbolting the exhaust before the cat to see if's plugged....

Need more beer, out.

 

Hmmmmm - OK - check if your EGR is stuck open. Open or partially leaking EGR at idle will cause all kinda of havoc - lean pops, funky idle, etc.

//RF

 

I hate to ask this, but is there any way to tell the position of the EGR valve by looking / feeling it?


The thought crossed my mind as I did unplug the vacuum solenoid when doing some tests off the bat -- but didn't check the valve itself.

86 on beer, out.

 

It is hard to tell visually - but a vacuum pump can be used to open - close EGR and see effects on engine idle.

 

Well got my cable and did a scan:

All sensors nominal - does this seem "normal" for a few minutes of idle:

IAC: 53
ECT: 140F
MAP: 48-49 KPA
RPM: 500-575
TPS:3%
IAT: 95F
BLM: 128
O2:500-550mv

Regarding EGR -- I was able to push up on the EGR Valve diaphram and the engine RPM increased by about 200-300rpm. Also, i could see exhaust coming from the rear of the engine bay while I had the diaphram open.

Must ponder over a cold one....

 

Your O2 should be bouncing from 200 mV to 800mV once engine is fully warmed (2-min+ and CTS ~ 180F). In this instance ECM is (probably) running in open loop (OL). Your MAP indicates slightly low vacuum level - usually on stock engines you see 28 to 38 kPA at idle (fully warmed ).

The fact that you could see exhaust gases at the rear of the engine bay when you press on EGR valve diaphragm may indicate leaky intake manifold gasket. The only place where you should see exhaust gases is at tail pipe! Do you have rear china wall oil leak????

//RF

 

To be honost, I'm SBC retarded -- I have no idea what or where the rear china wall is. No visible oil leaking from the motor, though.

Think we might be on to something....

 

"Rear china wall" refers to a rear portion of the block to intake manifold flange. When viewed from the top it has a (remote) resemblance of the Great Chinese wall. It is notorious for oil leaks when using stock or replacement gaskets. The best way to avoid leaks to lay-down 3/8" bed of RTV gasket maker (gray or black ) and set down intake manifold vertically. The trick to a leak free installation is to avoid side to side shifts, which is tough. I sometimes have to try 2-3 times before I get it right. Having a helper and aluminum intake helps.

//RF

 

Well, more developements, pulled the O2 sensor just to see if it was exhaust related, no changes in intake manifold vacuum, 46 kPa.

Did make a discovery playing with the EGR, I hooked the vacuum hose that connected the solenoid to the TBI Unit/Intake Manifold directly to the EGR -- the valve didn't move at all -- that make any sense?

I can't understand why I get a jump in rpm when pushing up on the EGR valve. You would figure when the EGR valve is opened the exhaust gas would drop RPM by a few hundred. I sprayed a good 2 cans of carb cleaner all around the intake manifold and didn't get any dips in RPM.

Where does the EGR connect into the exhaust on these cars?

Enjoying a Peroni by the pool...

 

The EGR has a passage port on the intake through the head. When activated, some exhaust goes back into the intake.

My tbi stock was getting 26-28kpa at idle. After a cam install, I'm up to 30-32kpa. Have you had any braking issues(hard brake pedal)?

 

No problems or irregularities with the brake pedal. I decided to bite the bullet, new intake manifold gaskets, tbi gasket, and egr gasket on the way.

Need to stock up on fine alcoholic beverages for this job...

 

Are you checking vacuum by aldl connector or by the intake with a mechanical gauge?

 

WinALDL, but I've changed out MAP sensors and the KPA reading at key on matches the weather reports.

I'm thinking it wouldn't be a bad idea to get a gauge / pump combo at Sears.

 

any updates?

 

I bring to you an update over an ice cold Warsteiner:

I picked up a pump/guage combo at Sears, took readings from the MAP line and the smog equpiement line source at the front of the TBI unit. Both read similar 15-16 in Hg.

Put vacuum to the EGR valve, it does open and hold it. The strange thing is, when the engine is running, I couldn't pull any vacuum on the valve. The only way to open the valve is to physically push up on the diaphram.

Thoughts?

 

The map sensor is suppose to read vacuum from rear of tbi port, closest to distributor.

 

You probably have a pressure modulated EGR valve. It may not respond to vacuum with engine idling due to lack of exhaust pressure. Im very curious also as to why you got an increase in RPM with the valve open. The injection of inert (exhaust) gas should make an engine almost stall at idle. Your ECT seems okay. That would have been my first question. When you connect your timing light you should check for drop outs in your spark, in association with the back fires. Im suspicious that you may have a bad pick up coil in the distributor. I have a 66 Elcamino to repair here at work. I will give this some further thought and get back to you later.

 

Err...yeah...hooked up the gauge and only pulled 15-16 in Hg...

Just read in the Hayne's the EGR Valve has a bleed hole governed by a spring which appearently bleeds off based on exhaust pressure. Makes sense now.

Picked up intake manifold and TBI to manifold gaskets....waiting for a good patch of weather.

Orders are coming up so I should be PCSing soon...wooohoo

 

Word Sampson,

It seems the car's pulling low vacuum, so my first thought is air getting into the EGR passage between the head and intake manifold. I'm guessing the relation to heat (problem gets worse as ECT climbs) might be the expansion of the gasket, increasing the leak.

Ironically, I bought a pickup thinking it may be ignition related, so, I may swap that over as well seeing as the distributor is coming out anywho.

 

RF Master mentioned O2 voltage. Your O2 is a single wire so its not going to cycle from 200-800mv at idle. A heated sensor (3 or 4 wire) will do that but the single wire requires higher rpm to heat it since it doesnt have its own heater. However, it should read around 450mv as this is neutral for O2 voltage. Any cycling it does should center around this point. The fact that it is centering closer to 525mv may be an issue. Try unplugging it and running the motor. See if the prolem doesn't go away. You may have a bad O2.

 

A note, an O2 sensor that reads high will cause a lean condition as the ECM pulls down injector on-time in an attempt to reach stoich. With your scanner, look at integrator and block learn. Are they high? (neutral is about 128). Perform the O2 test I mentioned above and watch for the intgrator to come down. Block lrean takes longer to correct as its long term.

 

BLM is 128, and I've disconnected the O2 to see if OL / CL would make a difference, didn't change anything. You would figure a vacuum leak = lean = higher LBM...

 

Actually as long NBO is hot (about 600F) it will provide output voltage (heated or unheated) at idle. Single wire O2s have a problem when installed in headers since headers tend to run cooler than cast iron exhaust manifolds. In OE O2 is installed within few inches of the exhaust ports - gases are still hot and cast iron tends to retain heat.

//RF

 

RF Master is correct in saying the O2 needs 600f to operate. Also about the sensor's range of 200-800mv, as well as the location of the OE sensor on our 3rd gens. It has been my experience after many years of diagnosing and repairing GM vehicles that single wire O2 sensors do not read dependably at extended idle. There is often not enough exhaust heat to keep the sensor at temp. This why we test O2 at 2,500 rpm. We can then allow the engine to idle and see accurate O2 output for a short time after returning to idle. When we see a single wire O2 sitting around 450mv at idle, its generally not a bad sensor but a cold sensor. However, as I said yesterday, 500-550mv may be a sign of trouble. Either a righ condition, which does not match the OP's description of the symptoms, or a bad O2 which is erroniously reporting a rich condition and causing the system to go lean.

However, if we were dealing with a bad O2 sensor, memcal should have corrected the problem when the engine was run without the O2. The exhaust at the back of the intake is puzzling. Do we know yet where this is coming from? That could very well be a manifold leak. I see now that we do have 128 BLM but what about integrator. As I said BLM is long term correction, integrator is short term. Do we know where it is. If BLM and integrator are normal, we may not have a lean condition at all. As I referred to before, the popping could be ignition. Have you tested for spark drop out yet? What youre experiencing sounds alot like an issue with the pick up coil and/or ignition module.

 

I pulled the distributor today, looks like the pickup wiring is a bit chewed up. I hate to admit this, but I can't figure out how to take the damn thing apart. I'll see if I can find anything here on Third Gen, if not, I'm setting this car on fire.

 

Well, if you have dizzy out you can strip it down to its basic components, by removing pressed in pin that keeps cam gear attached to the end of the shaft. The shaft can them be gently removed from the dizzy housing. -



After you remove the shaft you have access to reluctor retaining ring.



The pick up coil (aka reluctor ) sits under - in a white plastic cover as can be seen in the photo above. You have to pry off retaining ring (Delco part # 10488259) before you can have access to pick up coil (Delco part # D1987, OE 10495089). As always, a trip to a good part house should get you correct parts.

//RF

 

Thanks RF!

I'm so used to working with German cars that I was convinced there was a special tool involved. Glad to see it's actually...simple!

 

You welcome. In the past GM tried to avoid special tools, but that is no longer a norm since part designs coming from all the world. I would not touch today's Chevy without first looking at FSM!

BMW = Buy More Wrenches???

Just get a 5 pack of those rings - they are dirt cheap.

//RF

 

I don't know if you can tell in the picture, but it seems the leads aren't even touching the windings....

 

Leads are actually extension of windings. Reluctor coil is wound on the white plastic form. Photos do not show actual coil form.

 

RF,

Excellent instructions and photos on disassembly and repair of distributor.

BTW, every tech knows that BMW stands for "Bring My Wallet". LOL

 

Well, got everything put back together, turn the key and....cchkchkchkchkchckhckhckhckhckchck.

What a time for the starter to take a dump.

 

Darnit! So close too. A dead battery will cause the same starting issue. Did you try charging it?

 

Well, good news is, starter's fixed.

Bad news, my timing marks must have been....off.

I'm spoiled as I'm use to working on DIS/COP cars or ones with taped balancers.

Any advice on getting this beast back in time?

 

There are couple of ways of doing this, but almost always requires couple of tries to get it right:

1) Make sure that cyl #1 is at TDC On the firing stoke - remove #1 Cyl spark plug make sure that you can feel piston with a plastic rod (7-eleven straw works the best) and balancer mark is pointing to TDC. Use breaker bar to turn engine by hand (balancer center retaining bolt) - better rotational control.

2) Mark location of the #1 Cyl post on dizzy body (on Aluminum portion of the dizzy). Turn rotor CCW about 30 degrees from that location. Drop dizzy into the hole - rotor will turn clockwise when gear engages cam. The chances are that the oil pump shaft will require manual alignment to align with the bottom the dizzy gear. This is the PITA portion of the dizzy re-installation procedure. In that case get a BFS - 12 to 16" blade and reach down into the hole and turn oil pump shaft a little bit at a time. Repeat the drop and alignment of the rotor check against the cyl #1 marked position. Eventually all three positions will be in perfect alignment.

3) Secure dizzy hold clamp, but allow for dizzy to be turned by hand.

4) Fire engine - check and set timing. Let us know if you are victorious!


//RF

 

Hey Nate, I assume you mean that your distributor is out of time. This is a common problem when installing a distributor. I will try to describe the procedure for you as follows:

First, disconnect the ignition coil to disable ignition, then pull #1 spark plug. Now place your finger over the #1 plug hole while having a helper crank the motor. Shout stop as soon as you feel the blast of pressure against your finger. Look at the harmonic damper for the timing mark. If the engine stopped quick enough after you felt the pressure pulse, the mark should be close to the timing tab on the front of the motor.

If you dont see the mark, repeat the above until you do see the mark after the cranking has stopped(its sometimes helpful to paint the mark with whiteout to make it more visible). Then, using a 5/8" socket and a breaker handle, turn the crank so that the mark on the damper lines up with the big notch(TDC) on the timing tab.

Mark the position of #1 on the bottom of the distributor cap by locating the #1 wire and going straight down, then remove the cap, using your marker to transfer the #1 mark to the distributor base. Now, with the cap off, note where the rotor is pointing. If its pointing to the #1 mark or close to it, then the distributor is okay. Check ignition timing and firing order.

If its not pointing to the #1 mark, take note of how far it is from #1.
Is it 180 degrees off?

Next, loosen the hold down and lift the distributor out of the block, noting the movement of the rotor as you lift the distributor(this will help you when reinstalling the dist). If the rotor was 180 degrees off from the #1 mark before you removed the distributor, you should be able to simply turn the rotor 180 and the distributor should drop right into place. Remember how much the rotor turned as you lifted the distributor out of the manifold. This is the same distance you will need to have it offset from the #1 mark as you prepare to reinstall it. The rotor will again turn as you lower the dist into place. If you have it right, the rotor will line up closely with the #1 mark you made with the dist seated against the manifold.

If the rotor was not 180 from the #1 mark before you removed the dist. You will need to turn the oil pump drive shaft to line up with the distributor shaft as you install the distributor. The bottom of the distributor shaft engages the oil pump drive with a notch that looks like the tip of a flat screwdriver. The distributor and oil pump drive have to be aligned in order for the distributor to seat fully against the manifold. This can be tricky and generally takes a few tries to get it right.

Align the rotor for installation, remembering how much it moved as you lifted the dist out. Again, if its right, the rotor will line up with your #1 mark with the dist fully seated. If the rotor doesnt line up, turn it a few degrees (one tooth) and try again until it lines up. If the distributor doesnt fully seat against the manifold, the oil pump drive is not lined up. Use a long screwdriver to turn the oil pump drive.

Again, this is tricky as its hard to know just where the oil pump drive is pointed. If you pay attention to how things line up and try a few or several times youll get it to drop into place. Then install the cap, reconnect the coil and start her up. Reset your timing by disconnecting the EST connector and using your timing light. Clear codes when youre done by disconnecting the battery for ten seconds.

In conclusion, you may just have the firing order wrong so you dont have to deal with any of this or your timing may just be off. Otherwise your dist is probably 180 out. The oil pump drive will generally only allow the dist to be put in straight up or 180 out. So hopefully you at least wont need to deal with the whole oil pump drive issue.

Hope this helps, Doc

 

Thanks RF,

I noticed theres a tab in the gap from the waterpump to the block - I'm guessing thats the reference mark for the light? Also, I checked the balancer and couldn't find any easy markings...although there are V like marks?

 

Depending on the year and how much 'monkeying' PO did on the engine you should see sheet metal tab with V notches facing toward front of the vehicle. The outside circumference of the harmonic balancer should be partially abstracted by the timing tab. OE balancer usually has a single shallow notch traversing front to back. This notch is difficult to spot sometimes due to dirt and oil accumulations - I use white-out after cleaning balancer surfaces.

//RF

 

What RF said. Timing mark on balancer may be hard to find but youll know it when you find it. Its a deep notch running the width of the balancer and obviously machine cut.

 

The "0" notch on the timing tab is the deepest v notch. Its helpful to clean this tab well so you can see the numbers.

 

Well, got everything back in time, dropped the car into reverse andddd it still backfires out the intake -- but with avengenace (really loud wooosh)

Battery is kapput, so I'll be replacing that this week. The parts guy mentioned something about the TCC switch being stuck....not sure on that, but guess it's worth a shot?

Still two things that bother me: low vacuum and the engine revving up when pushing up on the EGR diaphram.

 

1) - TCC switch locks torque converter - highly unlikely. You can temporally disconnect 4 pin connector from trany (driver side on 700R4). This will eliminate TCC solenoid from the troubleshooting tree.

2) When you press on EGR diaphragm the valve should let exhaust gases into intake - slightly leaning out intake mixture and causing a bog (drop) at idle. In your case it is the opposite! You may have wrong EGR valve - take a photo of that bad boy or try to locate any part numbers that are stamped or printed on it.

//RF

 

just wondering if you changed the cts? in the manifold by the water neck. last time mine was running richer than hell wouldn't stay running unless i had my food on the gas. backfires, sounds alot like your problem. its a $13 part couldnt hurt

 

My old car use to back fire because the camshaft had some worn out lobes......

 

The TCC solenoid can leak or stick open, causing the TCC to remain locked with the car sitting at idle. However, this will simply cause the engine to stall. Like trying to stop a manual trans car without pressing the clutch pedal. It will not cause a back fire.

Ill do some research and be on this thread tomorrow.

 

Did you ever try openning up the exhaust? The affect youre getting from openning up the EGR at idle makes me wonder if you dont have a clogged cat. Try removing the O2 sensor. The small hole it inserts into will pass enough exhaust to make a difference. Just an idea.

Also, are you sure your CTS is reading right? You need a scanner to see it on datastream. You can test it with an ohmmeter but data shows you what the ECM sees.