Intermittent miss [understatment]

[Richard S]

This, unfortunately has been getting less and less intermittent on my 90 with 170k. It began a few months ago where the car would suddenly and without warning start to run like it was hitting on 3 cylinders. Limp home, let it set overnight, and it might not reappear for days at a time. When hot, there was an acrid smell, which I first though was burning wiring, but later appeared to be something dripping on the exhaust pipe, though I cannot trace its origin. I am familiar with the smell of most things when they hit hot metal, and this is different. When the car is in motion, it will lug badly and I have to shift down to get a gear that keeps the revs up which only cures the lugging. The car runs but misses badly. It might surge in and out of this condition, sometimes much worse than others. It also happens on cold start, at which times I can smell gas. I tried replacing the fuel filter, but that had no effect. I checked for codes, and it did not set any. I am thinking possibly a failing fuel pump. The car is also very sensitive to voltage drops, and I have been fighting a leaking battery that fouls the positive cable. Have to clean it every few months and I am wondering if the cable is corroded to the point where it will not carry the necessary voltage. That thing costs more and looks harder to replace than the fuel pump [i recently did a pump-in-tank Taurus, and it was not as bad as I thought it would be]. Final thought is a either pcm or dis module, though problems with that should set codes. The coil packs/module/plug wires are relatively new from when I installed MSD about 35k ago. Open to all theories.

[Roadster90]

I know the search function on the forum is a PIA....but try to type in "intermittent miss" (I have been told it will only work if you type your key word/s in quotes) and go back at least 2 years....look under my name for a post relating to the ECM.

Nic

[Guest Buick Mike]

I had a bad ECM which was holding an injector wide open. Some of your symptoms are similar to mine (lugging, intermittent occurances, smelling gas) but not all.

Mike

[Richard S]

Thanks, Nic. I was able to find your post. Besides the 90 Reatta/Riviera, does anyone know from what other cars/years I can use an ECM?

[harry yarnell]

I know the Riviera ECM's of the same years will interchange.

The smell----could it be the catalytic conv?

[Richard S]

Funny you should mention that, but there are about 3 bulbs out, couple in the tail light and I think one in the parking light. Certainly will replace them as the cheaper long shot. It is chilling to think this might be related to leaking battery/corroded positive cable. That looks like an ugly job and $70 for the cable and more for the battery which might still be under warranty. As to the CAT, I *think* I replaced that about 50k ago. Will have to check receipts.

[Richard S]

You are almost exactly correct, BH. The AC Delco cable for the 90 [sOX60-2SA] is about $95, while a new Delco starter is about $180. I don't see anything terribly unusual about the cable, though. It looks like a standard 2 wire 60" side post cable, maybe 6 gauge (?), except that the lug at the solenoid end is 90 degrees. Have others replaced the OEM with aftermarket, perhaps going to 4 or 2 guage? Perhaps I will make this a seperate thread to see what others think.

[Richard S]

Just to update. Replaced ECM. No change. Replaced bulbs, though this struck me as a sort of rain dance solution since I could not tie a failed bulb to this kind of performance disaster. No change. It is the intermittent aspect of this that is so mystifying. The car will sometimes kick in an out of its "condition", sometimes run well for miles, sometimes poorly for miles. I infer the actual performance problem has to be fuel related because when I first start the car, if it is not going to perform, I can smell gas. At its worst, when lugging, it feels like the transmission is slipping. If I floor it, the downshift is a terrible clunk. If I press the accelerator down without causing a downshift, it seems to respond much better. Since I replaced the TPS sensor a while back, I am thinking maybe there is inadequate voltage to the sensor, maybe a bad wire from the ECM [?] to the TPS? Does anyone know how to jumper that wire to test this theory? Any other ideas?

[Reatta Man]

Your problem sounds like a bad ignition module, located directly under the coil pack. GM had horrible problems with these when they first came out, and yours may be late in failing if you do not drive the car a lot.

Here's what to do:

1. Remove the coil pack.

2. Remove the ignition module, located directly under the coil pack.

3. Flip it over; if you see what looks like air bubbles caught in the epoxy plastic sealing the back of the ignition module, it is defective. The air bubbles are from excessive heat due to high resistance and high current draw in the module, resulting in partially melting the epoxy plastic.

4. After replacing the ignition module, I would recommend new plugs and wires if your current ones are more than 30-40K miles old.

5. If this does not fix the problem, you may <span style="font-weight: bold"> <span style="font-style: italic">also</span> </span> have sticking injectors. Remove the fuel rail and injectors and take them to a shop that specializes in fuel injectors. They will have a machine that runs a cleaning solution under high pressure until the injectors are clean. They can also do a leak-down test to see if they are partially sticking open.

Good luck.

Joe

[Reatta Man]

By the way, the injector service runs about $100 if you take them off, and about $150-200 if you have the shop take the fuel rail and injectors off of the car. This may seem like a lot of money, but believe me, it will make you think the engine is new when you drive it after they are cleaned and your other ignition problems are fixed.

[Richard S]

I replaced the module and coil packs when I installed the MSD system about 2 years and 50k ago. The original had indeed suffered a meltdown. I will, however, take a look at the module. It may be that they do not react well to having the MSD harness interface installed between the module and the coil packs. I will also do the injector service as this is probably long overdue at 170k. I do run injector cleaner through the tank periodically, but fuel quality is pretty variable here.

[2seater]

For what it's worth, I seem to remember Greg Ross had trouble with his MSD ignition system, although I believe his showed definite signs of trouble when it "barfed". I do not know if the MSD actually will contribute to degradation and more heat in the module and coil pack, since it just boosts the voltage to the coils, but it may do so.

[Guest Greg Ross]

You know about letting the smoke out, I assume. Everything has smoke(life)in it, if you let the smoke out, well....

Last September the MSD Module failed, starting the car one morning it sputtered and quit. Would not restart, then I see a column of smoke coming from behind the hood. Their install instructions provide no fusing at all. Richard, mine was installed with what they called the Grand National Interface Module, sandwitched between the I.M. and the Coil Pack. Simple installation, I think mine lasted for just over two years and 60 k miles. I still intend to ship it off to MSD for a repair quote, thereès a feature I only discovered after failure that would be an asset, variable timing option for the Supercharger engine.

Have you tried the bypass harness plug, would establish whether the MSD is at fault.

[Richard S]

Greg, I also used the Grand National interface. I am not sure if I have the bypass plug or not. I will have to check. The car alwasys starts instantly, but how it will run thereafter is the issue. Sometimes fine for a while, sometimes badly from the get go, or lack thereof. I certainly hope it is not the MSD. The installation on my Reatta was nothing compared what I am going through to put one in my 93 Olds CS convertible with the 3.4 twin cam. I am hoping MSDs prove to be either robust or invinceable. The module/coil pack is below the manifold and behind the starter, visible only from below and only then to certain species of legless reptiles. The DIS unit itself had to be mounted in a slightly modified space [thank you, air grinder] behind the headlight. At least it, unlike the coil assembly, will be kept cool. I was thinking of putting one in my Olds Aurora, but the cost of the coil interfaces is discouraging. If there are small mileage and performance gains, and I believe there were with the Reatta, it is not the hotter spark at the coil, but the multi-strike feature that is responsible. On the other hand, if that technology produces even small gains, why aren't they standard on high end ignitions?

[2seater]

Do you mean the smoke from the tires melting? MSD sells a pile of their different ignitions, and I can see some possible benefit of the multi-srike at low speeds (the only place it works) for possibly igniting lean cruise mixtures. The DIS ignitions we have is already far superior to a single coil system, and I rarely see an aftermarket ignition on the GN style drag cars until they get down in seriously fast territory, like 10 sec. 1/4's. I cannot say they don't work, we run MSD components on my sons off road race car. My only question is when I hear some aftermarket item gives dramatic results, but it is accompanied by other things when installed, such as new plugs and wires when an ignition upgrade is done. How much is the "black(red)box" and how much is the other new items that may have needed changing anyway? I am considering adding a system with individual cylinder knock retard, and a similar system is used on high end european turbo cars and the full zoot Corvette's.

[Richard S]

I am wondering if it might also be a failing fuel pump. My daughter's Taurus used to leave the car stranded occasionally. Even the dealer could not figure it out [wanted to charge me $150 for a $35 Idle Air Control Valve]. I replaced the in-tank pump and she has had no problem since. I am thinking that intermittently low fuel pressure might be the culprit. It just seems unlikely that at 1, 2, or 3 injectors would clog or fail at the same time, and less likely that all of them could mysteriously unclog simultaneously, sometimes for a few moments, sometimes for a day. On the other hand, the car does have a couple of "stages", bad and awful, which might correspond to one, two or three bad injectors. It is most likely to start and run normally for a while after sitting for a couple of days. I probably should invest in a fuel rail pressure tester. Likely it would cost the same as letting the mechanic charge to do the same thing. On the other hand, I thought low fuel pressure would set a code.

[2seater]

The ECM has no way to monitor fuel pressure, it is modulated by the vacuum operated fuel pressure regulator only. The fuel pump runs continuously, and the only connection to the ECM is through the start/prime relay. I drove around for a month with a fuel pressure gauge taped to my windshield while sorting out fuel pressure for my turbo install. It got a lot of strange looks. A kit shouldn't cost more than $30-$35, but you will have to extend the hose to get it in a position to read while driving. A cheaper alternative, is a #4 37 deg. swivel connection which will fit the pressure tap. You can buy one for a few bucks with a hose barb on the other end, and it will need to be a 90 deg. to fit with the hood closed. You just need a 100 psi pressure gauge which can be found for $6-$8, a few feet of fuel injection hose and a hose barb to connect the gauge to hose. The only "problem" with this cheaper alternative is you must remove the valve core from the fuel pressure tap to use it. The swivel fitting lacks the stud to depress the valve core.

[Richard S]

I decided to go with the pressure test. Got the fitting and forgot to get something to remove the valve core [tore the garage up looking for an old style bicycle valve cap with the tool on the end. In frustration, decided to bite the bullet and replace the fuel pump, which is my pet theory anyway. Turned the key to see how much gas was left. Nothing. Looked at the positive cable. So much corrosion it was frozen to the battery. Took my vice grips to get the lug off. Battery gets replaced along with positive cable. Having recently changed the pump in my daugher's Taurus, I was feeling like a veteran. Let me be the first to admit that changing out an in-tank pump with the car in the street is a no fun afternoon. I don't recall the manual mentioning dropping the rear sway bar, but that is essential. Lowering and raising the tank is relatively easy with 2 floor jacks. Thanks to baffling in the tank, fuel will not spill out of the filler unless you decide to do this with a good deal of gas in the tank. Of course, because the fumes are far more dangerous than the fuel itself, stopping the filler and return is essential. All-in-all, removing the postive cable and replacing the pump was about 5 fairly grueling hours. My wife said that I looked the perfect imitation of a turn of the century coal miner. Probably should have degreased the undercarriage before I started.

[padgett]

Have to mention, this sure sounds like a fouled spark plug (runs good when clean, bad when not) or an injector that sticks open sometines. Either will result in a gas smell.

Have you tried pulling plug wires (think you said those were replaced) when missing to see if it is just one cyl ? (Sometimes hard to tell difference, ECM will try to compensate). Ign module or coilpack will generally affect two at a time (1&4, 2&5, or 3&6) since there are only three coils.

Coilpacks and ignition modules rarely come and go, when ded they stay ded.

[Richard S]

Great minds think alike. In searching, but not finding, the receipt for the battery, I did find the receipt for the plugs I bought in '01. My wife says I probably could have saved myself a good deal of agony by just replacing plugs. Like a fool, the utterly intermittent nature of the problem [sometimes at start up, sometimes not, sometimes a few seconds on and off, sometimes good for a day, bad for a day] convinced me it was not plugs. In the course of removing the positive battery cable, I did manage to check the plug wires where they are routed under the injection rail cover and all looked good. It is time for the plugs, though, so I will replace them. I was running Bosch IVs, but many people have written to say they don't like them in the 3800 engine. What do you recommend?

[padgett]

I like Rapidfires (now platinum) #3s for Magnavox ignition, #14s for Delco or "improved". If you need any other parts the best deal seems to be from GMPD. Savings on even one set of six plugs over neighborhood chains balance the s&h hit at least that is how it worked out for me.

If you have one plug that has been fouling/misfiring, it should be obvious when removed.

Unless recently done is also a good time to change the O2 sensor. There I have used both Bosch and AC. Both work about the same but the Bosch is enough taller that it must be removed to get the #6 plug out. AC doesn't.

[Richard S]

Took a look at autopartsgiant.com and see the platinum AC Rapidfire at about $6.50 a plug while the Bosch IVs are $4.50. Also see the NGK Iridiums at over $12. Can one really justify that price in terms of performance/longevity? How do these prices compare to gmpd? BTW, the 02 sensor was $18 and change [there is a KEM for $16, but I don't know that brand]. They don't charge shipping, but do charge sales tax in CA and a handling fee of $3.

[padgett]

Those prices are absurd or Canadian. Pep Boyz/AZ/Advance all have the Rapidfire for about U$4.25 ea. From GMPD they were U$3.10 ea. on my last order the set of six (p/n 25332828 for #14s) was U$18.60. Of course the S&H made it about the same as anywhere else but could add other parts to the order for less.

For someting I only do at about five year intervals, the price is reasonable.

[Richard S]

Having dined last night on crow, it is only fair that I bring this saga to its fitting end. To those who said, in so many words, "Probably that damned MSD igntion module", my hat is off and in hand. After replacing the ECM, the fuel pump, the plugs, the positive cable, the battery that as continually corroding the positive cable, cleaned the injectors and replaced the o-rings [An odd tale in iteself. There are 2 o-rings and two spacers to each injector. The larger o-rings, top and bottom were fine. Those are available. The plastic "spacers" on each side of the bottom o-ring, are of two colors: Tan and black. The tan were fine; every black one crumbled to dust at the slightest touch. Neither of the spacers are available in any kit and are not sold separately even by GM. Counterman said I can get them IF I buy a complete injector. Can this be true, I asked myself as I substituted another o-ring??!!! But I digress.] I was still stumped. Replaced the pcv valve, just for good measure. Finally got ahold of an MSD bypass plug and, as a final, last-ditch, before-we-limp-off-to-the-REAL-mechanic try, I plugged in the bypass plug. Car immediately ran fine. There is both a moral and a moron to this story. The moral: Do ALL the simple things first. The moron and author are one and the same.

[Guest Greg Ross]

<span style="font-weight: bold">Yer welcome!</span>

Been there, done that only mine was spark plugs as it turned out, and since the very last work done around the engine compartment had been regapping the platinum plugs from .060 to .035

But it is the best way to learn!

[Richard S]

When last I approached the forum, hat in hand, I had replaced fuel pump, battery, positive cable, o2 sensor, plugs, pcv valve & ECM, injector seals and service. Finally just disconnected the MSD ignition after which car ran wonderfully for about a week. Suddenly it starts missing and spewing smoke from the tailpipe like it is running rich, smell heavy gas odor in cabin. Put timing light on each plug wire and each is firing. I am obviously running horribly rich, probably fouling plugs. Even looks like gas coming out of the front manifold to downpipe connection. So I replaced fuel injector pressure regulator. No change. Why all of a sudden? Why me? Why?

[padgett]

Offhand first things I would check via the onboard diagnostics are the (no particular order) Coolant Temp, TPS, MAF, IAC, O2, BLM, and Fuel Integrator readings because something sseems to be lying and those are the most likely indicators of what.

If it were here, I connect a laptop to look at all of them at once and record a few frames but you need to work with what you have.

[Machiner 55]

For Padgett:

How do you connect a laptop to it and what program are you ruinning that allows you to "see" what's going on?

For anyone:

Can someone tell me what is supposed to be connected to the reservour located under the air cleaner on the left hand side of the engine compartment.

In advance thank you for your time.

[padgett]

a) Resovoir contains reserve for HVAC and cruise control so you won't lose a/c on a brief WOT condition.

For many years I used the Diacom cables and software but have recently purchased Craig Moates stuff which is cheaper (about $100 for the connector and adaptor) which has the advantage of using a non proprietary format and a USB connector.

c) Also the OTC 2000 scanner (I have two) has an optional laptop connection cable that appears rarely. You do need to be able to emulate a VT-200 terminal for best viewing. It and the Diacom cables require an RS-232 port.

Has not been often but sometimes I need to be able to capture a series of frames when a car is acting up while driving, it how I diagnosed a TPS wire that was separating under braking only.

[Machiner 55]

To Padgett:

Thanks for the info regarding the laptop connection. Very informative.

Regarding the reservoir... I found that it was disconnected when I bought the car about four weeks ago due to the fact that the barbed connector on the tank itself was broken off. I managed a repair but didn't know where to route the line from the tank. I still don't know and I can't find any details or photos in the service manual. There were a couple of vac lines disconnected by the previous owner for reasons unknown to me. The cruise control didnt work untill last night when I routed a formerly plugged (with a machine screw) vac line located after the tee on the check valve to the cruise control solenoid located under the air filter breather tube. I don't see any other disconnected lines so I don't know where to connect the reservoir tank. Is there another tee somewhere that I'm missing?

[Machiner 55]

OK.

[padgett]

Discharge of resovoir goes to cruise control and to the HVAC programmer (if that line is bad, air will alwways come out of defroster vents).

[Machiner 55]

Can someone tell me where the tank ties into the vacuum system?

I guess I'm needing a picture drawn. The schematic of the vacuum system placarded on the RH strut tower doesn't depict the reservior. So, I'm wondering where exactly the tank ties into the system. I'd like to configure it as it was when it left the factory.

Just a note. In the last 48 hours I got the cruise control to work again as well as the air conditioning. The plug or "pigtail" that connects to the compressor was disconnected. For the life of me I don't know what the previous owner was doing with this car!

[Machiner 55]

Can anyone tell me where the tank ties into the vac system?

[Guest DTerry]

I haven't a clue how to attach a picture, so I emailed you a description with photos.

[Machiner 55]

Cool... I anxiously await the mail. Thank you very much.