Occasional stall right after startup...

Patient (or victim ) is a 1993 Chevrolet Caprice Classic wagon, L05 TBI 350 V8 engine, probably running on original cap, rotor, plugs and plug wires...not absolutely certain of that...

The car runs fine in every way, gets exceptional fuel economy and does not seem to lack for power but it has recently picked up a habit of running poorly immediately after startup when warm. It happens only occasionally. The engine will stumble momentary and will sometimes come back to a normal idle or it will stall out. I've not yet verified it to my satisfaction, but it seems like putting my foot in it just a little right after it fires will keep this from happening. If it recovers, it continues to run perfectly.

If it stalls, and I restart it, the engine runs perfectly.

The check engine light has not come on. No codes are stored.

I'm thinking that the fuel filter is a possibility, though I'm reluctant to change it as I have this feeling that I will be setting myself up for a sinking feeling when I twist a line off. I do plan to treat the car to some new plugs, wires and a cap/rotor combination in the near future. And I will change the fuel filter, whether I want to or not.

How bad are the plugs to do on these cars? Some of them do not look to be easy to get at.

Plugs are easier than they look. I just replaced my original wires and that wasn't bad either but I did use a good AC Delco set from RockAuto that had all the correct ends and lengths as some are straight and others have 90° ends.

Check your vacuum line to the EGR, I found mine broken, and it may have been the culprit. I can not verify that, because I am in the process of an engine swap. I found the broken vacuum line while removing the old engine.

Mine would not start when hot after sitting for about 1/2-1 1/2 hours. It would kick an buck for about 20 seconds as I played the gas pedal, then run perfectly.

Note: EGR valve should NOT have any vacuum at idle unless the control solenoid valve is faulty. A broken EGR vacuum line would create other issues, especially at cruise speeds when it is in operation; i.e. spark knock, pinging, detonation or whatever you choose to call it.

As eluded to; make sure your ignition system is up to it's full operational potential. May be time for a tune-up, as mentioned. For each additional .001" (one-thousandth's of an inch) in the plug gap wear, the ignition coil will require additional voltage for a proper spark to occur. (When viewing on a scope you would see less burn time.) A cold engine is more demanding on the ignition system to fire the rich air/fuel mixture, as would WOT operation. Increased plug gap reduces actual burn time at the plug gap as more voltage is used to fire the plug than to keep the fire burning in the gap. Many items could cause the concern you mentioned and the ignition is only one of them and fault could lie on either side of the system, primary or secondary.

Before you get too deep into it, check your oil pressure switch. The one on my LO3 went bad and caused the fuel pump to act wonky. Once the RPMs picked up, no issues. Didn't fail altogether just intermittently. Took me a few days to diagnose but had similar symptoms. Try running it with the fuel pump jumper connected. If it corrects the problem, change out the pressure sender.

Bill

gmtech wrote:

Note: EGR valve should NOT have any vacuum at idle unless the control solenoid valve is faulty. A broken EGR vacuum line would create other issues, especially at cruise speeds when it is in operation; i.e. spark knock, pinging, detonation or whatever you choose to call it.

As eluded to; make sure your ignition system is up to it's full operational potential. May be time for a tune-up, as mentioned. For each additional .001" (one-thousandth's of an inch) in the plug gap wear, the ignition coil will require additional voltage for a proper spark to occur. (When viewing on a scope you would see less burn time.) A cold engine is more demanding on the ignition system to fire the rich air/fuel mixture, as would WOT operation. Increased plug gap reduces actual burn time at the plug gap as more voltage is used to fire the plug than to keep the fire burning in the gap. Many items could cause the concern you mentioned and the ignition is only one of them and fault could lie on either side of the system, primary or secondary.

The vacuum line itself will cause issues irrelevent of the EGR valve, and its role. With a vacuum leak, the engine will act in an unusual manner, and could cause hot start issues. The engine is running out of loop, and the "base setting" for the IAC valve may be too lean with another vacuum leak, causing a non ignitable mixture...His position of the throttle pedal to keep it running may allow the mixture to be rich enough to combust. The EGR valve is not involved at this point, probably should be ignored, and would not function if the vacuum line is broken anyway.

OK, some clarification as to what I was saying. EGR vacuum is ported from the throttle body, from the throttle body a line then connects it to the EGR Solenoid, from the EGR solenoid another line then connects it to the EGR valve. See illustration. The EGR has no function or role at an idle condition.

[You must be registered and logged in to see this image.]

A break or removal of the line from the EGR solenoid to the EGR valve will have absolutely no affect on the engine at idle. UNLESS the EGR solenoid is allowing vacuum to pass through due to improper vacuum hose routing and/or, in which case the EGR solenoid or circuit control is at fault (keeping the solenoid energized all the time). The EGR solenoid is a N.C. valve. The EGR does not receive direct full manifold vacuum to the top of the valve (engine would run very rough and be belching black smoke from the tailpipe at idle).

Vacuum only reaches the EGR solenoid with the throttle depressed, hence "ported" vacuum. When commanded from the ECM, only after the correct engine operating temperature has been reached and proper operating conditions exist will the EGR solenoid be energized. I agreed with this statement "The vacuum line itself will cause issues irrelevent of the EGR valve, and its role." Only when vacuum is present in the EGR vacuum circuit and only in an off-idle operation and in most cases vehicle speed will need to be present.

Now, with a break in the vacuum line from the throttle body to the EGR solenoid, issues may ensue, but only when the throttle plate is cracked enough to create "ported" vacuum.

Most of these TBI engines operate in open loop at idle due to the oxygen sensor cooling off, non-heated single wire O2 sensor.

If the line is broken between the solenoid and the throttle body it will cause the mixture to go lean, and could cause the hot start issue. The IAC valve will try to compensate for the extra air, but it may not be able to without raising the idle speed, or it may not run at idle. Opening the throttle valve will tell the coomputer to add fuel, and it may run at a higher RPM than idle.

Just spray a little cleaner thru the iac,.its lazy,.

nIck

I,d like to see a tbi owner add the grooves to the tbi, as is touted by gadgetman,.be interesting.

i am actually having the same problem.. came one here to check it out.. from cold it starts fine.. gets hot stall out.. use to spudder when i was in gear and just run terrible at low rmps.. i step on the throttle it would be fine.. on my way to work it stalls out.. could not get it to run.. i put a new fuel injector relay cause there was no fuel spitting out the injectors.. as soon as i changed it.. it was fine for about two minutes then died.. now it wont turn back on.. trying to find a spare spark plug but no one is home to take me for a ride and all my buddies are out drinking and not home to get one for me.. cause i was thinking maybe now its a spark issue rather then a fuel issue.. but if im cranking my engine over shouldnt it still be spitting out fuel from the injectors.. i have the same engine.. TBI 350 only mines a roadmaster 92

i jumperd the oil pressure switch.. jumperd the fuel pump.. jumperd the fuel injector relays.. pulled the map sensor to see if it would run crappy.. and it still ran fine for two minutes before now it wont start.. i have fuel in it.. the only other thing i can think of is the idle air control on the throttle body itself?.. how does that work?.. not really sure how it regualtes the fuel/air mixture

could an egr valve cause it to stall out maybe?.. sorry im blowing up your post man but im excited to see the same problem.. i got work sunday night so i gotta get this thing going A.SAP!..

so i did some research.. i think im gonna go with the ignition control module.. cause that controls the injecter pumps if im not mistaken?..

I just found that I had a couple of ground wires broken behind the passenger's side head. They are the ground for a number of essential modules. Check them as well. One wire is black/w white stripe, and the other is tan. The ground is G104.

WagonLover wrote:

could an egr valve cause it to stall out maybe?.. sorry im blowing up your post man but im excited to see the same problem.. i got work sunday night so i gotta get this thing going A.SAP!..

Pull the air cleaner lid,.while the car is idling watch the injector spray pattern both sides should be a uniform mist,.
if one side is dripping,. its flooding slightly when its hot, and the iac isn't catching it quick enough,.
Poor spray pattern on TBI is very common,. poor fuel mileage, will not pass emissions etc,.
very common problem,.starts good cold because its getting extra fuel,.

doubt you have a spark problem,.poor spark shows up with cold starts,..

Nick,
I,m not an expert,. or a moderator, but i,m surrounded by them,.

phantom 309 wrote:

Just spray a little cleaner thru the iac,.its lazy,.

nIck

I,d like to see a tbi owner add the grooves to the tbi, as is touted by gadgetman,.be interesting.

Curious what the grooves to the TBI are all about?
Thanks

The ground at G104 is the ground for the ESC module (brown wire), as well as the fuel pump relay, ECM, power steering pressure switch, cruise control module, and instrument cluster (black /w white stripe).

uxwbill.. any progress?.. i need ideas.. we must get the culprit!..

im following a wire scamatic off haynes.. is that any good?..

Flasheroo wrote:

phantom 309 wrote:

Just spray a little cleaner thru the iac,.its lazy,.

nIck

I,d like to see a tbi owner add the grooves to the tbi, as is touted by gadgetman,.be interesting.

Curious what the grooves to the TBI are all about?
Thanks

[You must be registered and logged in to see this link.]

Sounds like a load IMO.

it worked!.. the esc module.. purrs like a champ.. the module on the distributor..

50 bucks at autozone part number is DR140

Olds Weighty Eight wrote:

Sounds like a load IMO.

Try on your TBI ,. mebbe debunk the myth,.

Mr. "gadgetman" had his scheme tested at Automotive Testing Laboratory in Mesa in accordance with the "Federal Test Procedure Highway Fuel Economy Test.

The regulated pollutants all increased
fuel economy decreased
The check engine light came on and stayed on during the testing – 4
codes were in the computer memory:
#14 – coolant temp high
#32 – EGR
#35 – IAC
#45 – O2 rich

When this was made public, he blamed the vehicle, saying it was worn out and required repairs. Why he would submit a worn-out vehicle as the test bed was never really explained. Why he hasn't had the test repeated with a reliable vehicle is equally unexplained.

However, he uses Google's automated robot services to notify him when his name appears in a forum, so no doubt he will be along here shortly to tell us how wonderful it all really is and offer a slew of testimonials and technical jingo in lieu of scientific data.

buickwagon wrote:

Mr. "gadgetman" had his scheme tested at Automotive Testing Laboratory in Mesa in accordance with the "Federal Test Procedure Highway Fuel Economy Test.

The regulated pollutants all increased
fuel economy decreased
The check engine light came on and stayed on during the testing – 4
codes were in the computer memory:
#14 – coolant temp high
#32 – EGR
#35 – IAC
#45 – O2 rich

When this was made public, he blamed the vehicle, saying it was worn out and required repairs. Why he would submit a worn-out vehicle as the test bed was never really explained. Why he hasn't had the test repeated with a reliable vehicle is equally unexplained.

However, he uses Google's automated robot services to notify him when his name appears in a forum, so no doubt he will be along here shortly to tell us how wonderful it all really is and offer a slew of testimonials and technical jingo in lieu of scientific data.

Please post a link to this info,.thanks

Nick

Hmmm. Looks like the gadgetman has removed all reference from his website. He had publicized in advance that the tests were being conducted, and he did post the results eventually (basically, he had no choice) but now they have quietly disappeared.

Ok, Google produced [You must be registered and logged in to see this link.]. Gadgetman participated in the ensuing discussion. If you scroll about half-way down, you will find an e-mail from the testing lab to gadgetman quoted:

"Subject: f inal result
Date:T hu, 22 Jul 2010 15:51:09 -0700
From:G regory R. Barton
To: gadgetman @gadgetmantechnologies.com

Ron,
Attached is the spreadsheet of results updated to include today s [You must be registered and logged in to see this link.]
The regulated pollutants ALL increased, fuel economy is up slightly,
but still below baseline level.
The check engine light came on and stayed on during the test – 4
codes were in the computer memory:
#14 – coolant temp high
#32 – EGR
#35 – IAC
#45 – O2 rich
Not the results you were looking for, but further proof that the
Aluminum Falcon is not a suitable test vehicle.
Greg"

While I may not have a link to the test results, I do have them saved on my own harddrive, and will attach the pdf to this message so you can see the actual numbers.

Or not. Can't seem to find a way to attach a file here, just pictures.

Ok, converted the pdf to a jpeg:

[You must be registered and logged in to see this image.]


Now WHAT FOLLOWS IS PRIMARILY CONJECTURE ON MY PART:

I think that the groove can produce some results, at least temporarily, in certain cars of a certain vintage. Not because it is making the engine more efficient but because it fools the ECM/PCM for a time and fools the driver as well. His groove is a semi-circular groove cut into the wall of the venturi below on half of the butterfly. Ostensibly, this causes turbulence which improves vapourization and somehow changes the vacuum throughout the engine.

Now, increasing intake turbulence is a tried and true "porting and polishing" trick from the old days of carburettors and even TBI cars. Up to a point, a bit of turbulence does have that effect by enhancing mixing and allowing engine heat to vapourize small droplets more efficiently. For a while in the early 80's, Yamaha equipped some of their models with the Yamaha Induction Control System to do something very similar. It had a measurable effect, but only within a limited rpm band. They later went to multi-valve heads which had a greater effect over a broader rpm range.

So, first of all, I don't see any way this could possibly benefit a direct-injected engine. The fuel doesn't meet the air until it reaches the cylinder and by that time, any turbulence has been lost in all the other turbulence caused by the intake tract. The injection process itself causes efficient turbulence in the cylinder, where it really matters. However, there will still be a roll-on effect felt by the driver. As the driver touches the gas pedal, the butterfly begins to open. Instead of the relatively small gap between the venturi, the edge of the butterfly will now expose the groove -- a much larger gap, equivalent to pressing much harder on the pedal. So the driver feels a surge of power with just a tiny input and thinks the system has made his engine more powerful. In closed loop operation, the O2 sensor will adjust the short-term fuel trim to suit the airflow and eventually the long-term trim will catch up. With today's PCM systems, the long-term trims even effect the open loop fuel mapping so any effect the groove may have on the contribution of manifold vacuum pressure to the overall open-loop fuel map will soon be negated.

In an older vehicle, with a less sophisticated fuel management system, I think the groove stands a better chance of fooling the system for a longer time, particularly in open loop mode. Even a system that automatically re-zeros the TPS at key-on will be fooled since the butterfly stops short of the groove. So when the system computes the fuel mixture based on throttle position, it has no way of accounting for the additional air flow through the groove and the resulting injector duration will be running the engine lean. TBI GMs will utilize the long-term fuel trim in that calculation, so eventually the mixture should return to normal, but some early fuel management systems defaulted to the hard-coded fuel mapping in open-loop mode, so they would remain lean indefinitely. Those systems with singe-wire O2 sensors usually remain in open-loop mode until the sensor starts to function. One might think that the system would throw an O2 sensor code under those conditions, but so long as the O2 sensor functions occasionally (as during acceleration when the throttle is opened wider and the percentage of air added by the groove is greatly diminished) the timer is reset. Under part-throttle cruise conditions, the engine could be run lean, increasing the fuel economy.

It is well known that the stoichiometric (14.7:1 ) air/fuel ratio is NOT the most fuel efficient. It is necessary to sacrifice a bit of fuel efficiency to ensure acceptable emissions. Running lean (aside from engine damage issues from elevated combustion temperatures, knock, etc.) generates excessive nox -- the principal cause of smog. The cat converter can remove the most of the nasty emissions, but only if it is properly fed with the correct proportions of HC, nox and oxygen. In a way, gadgetman has a point about burning fuel in the cat converter. It's not "burning" in the sense of open flame, and it's not raw gasoline, but it is an oxidizing chemical reaction of the products of the previous combustion process. Of course, unlike simple combustion, it's a 3-way reaction requiring the correct proportions of all required chemicals (in the presence of unconsumed catalysts). To ensure the correct ratios reach the cat, it is necessary to burn SLIGHTLY more fuel -- about 1% more fuel. Short periods of rich or lean running can be accommodated, as the cat has a certain storage capacity, but eventually that capacity will be reached, leading to cat failure.

In conclusion, I think that while gadgetman may well fully believe his own hypothesis, his results are unproven and based on an incomplete and inadequate understanding of the systems involved. His credibility is further compromised by his contention that the process will not void any warranty because it is completely reversible with epoxy! Before I would consider screwing up my own car with this groove, I would want to see a lot more than some testimonials from his equally uneducated customers. To start with, a documented test regime including full datalogging (including engine load, tps, rpm, MAF/MAP, fuel trims, and wide-band O2 sensor in addition to just emissions and fuel consumption) of a variety of subject vehicles under controlled and reproducible conditions. Unfortunately, this would not be a cheap proposition and it's unlikely he can support such a program. However, if there was really anything to it, he could patent and license it to someone who can afford it -- like GM or Ford.

Anyway, this has grown far longer than intended, so I'll step off the soapbox now...

I,ve now read the gadget man chronicles, his mods with epoxy and groove seem to benefit the gm 88-95 tbi
and then he has tried to convince the world he has a holy grail,.that works on every vehicle,.

Thats why i,d like to see a tbi wagon modified,.

Some folks say the TBI spacer works too ,but i don't know of anyone with a wagon ever trying it,.

The 88-95 TBI system is a dog as we all know,


nick

phantom 309 wrote:

The 88-95 TBI system is a dog as we all know,

Based on drive-ability, torque curve, peak power, fuel mileage or all of the above? I will say that Buick was light years ahead with the distributorless, fully-sequential, port fuel injection they were producing by the early 80s.

Having the same issue - stomping the gas seems to fix it. Would be interested what everyone else finds to fix it.

Wow, this is a heavy discussion, way out of my reach. I just turn the key and go, but on the other hand, I appriciate the guys who do all this just to improve their wagons.
Respect
Pete

WagonLover wrote:

uxwbill.. any progress?.. i need ideas.. we must get the culprit!..

To answer your question...it was a few days before I could get back to it...

I drove the car again today and expected it to act up, but it never did. My driving pattern was similar to the day when it misbehaved. If I read your posts right, I don't think it behaved quite like your car has been. I never had any problems with it other than at startup. Once running, it stayed running. If it acts up again, I'll have to look into it once more, but so far, it's running fine again!

I looked at my vacuum lines, and the only leak I know of is in the one leading off to the climate controls. But that's been leaking somewhere ever since I bought the car, and I really don't think it could leak enough to throw things off. (The climate controls are working except under heavy acceleration.) I have yet to check on the spray pattern of the fuel injectors. I do plan to install new plugs, new wires, cap/rotor and even a fuel filter.

WagonLover wrote:

im following a wire scamatic off haynes.. is that any good?..

Well, I suppose the schematics are at least somewhere around usable, but if you want my honest opinion?

(Beware, I'm going to be brutally honest here.)

I would put that Haynes manual aside and get the GM factory service manual for your wagon. You can buy it new, which is sorta expensive but probably well worth it or you can often find one on eBay. I got mine for about $15 or so, with a little more for shipping. It's worth getting the factory service manual for the far better diagrams, procedures and troubleshooting trees.

WagonLover wrote:

im following a wire scamatic off haynes.. is that any good?..

What wiring diagram is being sought? Let me know what and maybe I can help you out with a factory wiring schematic.

phantom 309 wrote:

I,ve now read the gadget man chronicles, his mods with epoxy and groove seem to benefit the gm 88-95 tbi
and then he has tried to convince the world he has a holy grail,.that works on every vehicle,.

Thats why i,d like to see a tbi wagon modified,.

Some folks say the TBI spacer works too ,but i don't know of anyone with a wagon ever trying it,.

The 88-95 TBI system is a dog as we all know,


nick

2 things I know to be true from these post,the first is that this gadgetman is very much in love with the sound of his voice and secondly
the TBI is a dog we all love to love!

I know this is an old thread, but I figured I'd throw in my 2 cents.

I had the same problem with my 92 TBI wagon, but ONLY on abnormally warm days when winter blend fuel is still being used. Get it up to operating temp, let it sit for 45 minutes to an hour, and it would stall immediately upon startup. Cranked it again, and ran fine after I gave it gas.

I did some research in the service manual, and on the TBI units, once the car is shut off, the fuel pressure goes to zero (there is a bleed-off valve in the TBI unit). So, my theory is, since the pressure is released, the winter blend gas (which vaporizes more easily in warm temps) can easily vaporize on a warm day.

In fact, I remember reading that one GM TBI car (not a caprice) had a special 20 second purge cycle for the fuel pump, in case vaporization occurred.

This never happens in the warmer months, when summer blend gas is used.

This wouldn't explain a start/stall problem with 94-96, as those have built in fuel pressure regulators on the line.

Again, just my 2 cents