Alfa Romeo Forums banner

1 - 20 of 20 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter #1
I am an automotive tech that works for an idependent shop in the Dallas area. Usually, I work on high-end German makes (certified on Mercedes). About 6 or 8 weeks ago an exasperated client, new to the area, brought an early production '91 164L to us because it was cutting out/bucking/stumbling on acceleration. The symptom would start about 4,000rpm, give or take, and once it would start, it would not stop until you let off the gas, at which point, once the rpms came down some, you could ease back into it. Occasionally, the symptom doesn't occur at all and it'll pull strongly to redline. I have checked all of the grounds that I can find to check and have pulled out the Motronic module and clean the contact pins on the module as well as on the plug. I have put in a new coil, at least for test purposes and I have also replaced the RPM sensor as I found the old one with a dinged casing. All to no avail. I have spoken with the technician that she was using where she moved from, who is quite familiar with the car and he suggested that a wire or harness was chafed and so was shorting to ground causing a loss of power to the Motronic module (the reason the tachometer bounces/dies when it acts up). Not sure I completely agree, but am out of options, I re-checked the grounds and find them to be visually intact. I only have two service books for the 164 which I've borrowed from another independent here, but some of the notes from one don't correspond to the other so I figure there are other books I don't have. I have other diagnostic equipment such as a Bosch KTS300, but don't know where the diag connector is, if there even is one (her previous tech said there isn't one). I also have a Bosch interface (like a socket box) for the Motronic unit where I can plug in between the Motronic and the harness, both of which are new to me as I came from a dealership. The CEL has never come on (even with the test button) so I can't do a self diag.

Like everyone on here I'm a sucker for Italian cars. However, I have an Italian bike (Guzzi), but not an Italian car. I would REALLY like to help this poor lady, and I've had her car FOREVER, but I'm obviously limited on diag resources and at the end of my chain on this.:confused:

Thank you in advance for any tips!

Michael
 

·
Premium Member
Joined
·
27,375 Posts
1.Have you checked big black corragated hose between AFM and throttle body for cracks in corragations and at clamps and is AFM/Air cleaner box rubber mounts solid or sheared off?
2. Have you checked rotor and spring loaded carbon button inside dizzy cap?
3. Have you checked ignition switch for intermittent contacts? Jump red power wire to brown wire for ECU/Coil at connector located about above driver's right knee to see if problem goes away.
4. Have you checking for a binding flapper valve inside air flow meter? If binding and since car is a 164B/L flapper has 2-piece vane you can lossen screws to recenter and free up binding.
5. Have you verified S11 ECU G131 grounds at end of intake plenum (front of engine) and ground strap from intake plenum to rear head located under throttle body?

Self test Alfa 164 Motronic Self-Diagnosis using SQUARE button on side of steering column cover.
 

·
Registered
Joined
·
3,120 Posts
I hate to suggest this but my 91L displayed intermittent symptoms like this in high humidity and low air pressure conditions. I never di discover why. The fault only appeared at high elevations and in damp weather. Weird and it hasn't done it recently.

Unless this problem is persistent and chornic I advise that she pull over, shut off the engine, restart and drive. I did find some correlation to the fuel filler cap in that if I also undid and redid the fuel filler cap the problem would usually go away.

Perhaps it is some quirk associated with the fuel vapour recovery system which has an unusual tank in the trunk and an electronically controlled charcoal filter vapour trap in the left front fender.
 

·
Registered
Joined
·
1,765 Posts
I like Steve's suggestion of the sticking airflow meter flap best. I had very similar symptoms in a different car, with Bosch LH-Jetronic injection, and it was exactly that cause. Come to that, I had the same symptoms/cause in a mechanical-injection K-Jetronic car, so it definitely happens.

Because the airflow meter is the main input to the injection system, it stands to reason that it will affect the fuelling very quickly if the signal is wrong.

At the same time, if the flap is sticking, the signal would still be within normal bounds, so you wouldn't expect a fault code to be triggered. And if 'eased back into it' (as you describe), the airflow meter flap may very well respond correctly and give normal behaviour.

-Alex
 

·
Registered
Joined
·
11 Posts
Discussion Starter #5
Many, many thanks for the speedy response and the invaluable list of things for me to check! I have already checked the cap and rotor and they are spankin' new. Yesterday, after I got your reply, I removed the air filter housing lid/airflow meter assembly and checked movement of the vane which did not bind at any point in it's travel so no adjustment was made. I did, however, wipe out the oil and dirt while I had it out and then got sidetracked in our dyno room which is being serviced and re-worked. This morning I rechecked the grounds on the side of the intake plenum, both of which merge with the larger harness that goes into the firewall. I did NOT find, a ground that goes to the rear cylinder head. I found where the fuel return hose used to be secured in a holder to the rear cylinder head. I have looked and looked for a wire with no home or one that looked out of place, but did not find it. The corrugated hose is starting to look a little old and rotting, but it is intact. No separations.

One more thing I intend to check is the O2 sensor to see that it's working properly. The problem is so consistent that I don't see it being a type of thing where you hit a bump and it quits working. It's more like fuel starvation and the engine leans out till it's choked. Yet, I have fuel pressure even when the car is bucking. My thought is that the O2 sensor is maxing out rich so the Motronic is leaning out. Perhaps I'm off base, but seems to make sense with the car acting the way it is.

Thank you again for the education! It is just in the nick of time. She's due to pick up either this afternoon or tomorrow.

Michael
 

·
Registered
Joined
·
4,054 Posts
The CEL should light if the O2 reaches max or min adjustment range (too lean/rich) 1-2-2-3 code. The most common fuel system related problem this car has is a short length of hose in the tank can split and cause problems mostly below half a tank of gas or so and cause hard starting mostly when warm/hot and poor performance. The fuel pump would have to be pulled to replace the short length of hose with submersible fuel hose. There is a grommet that seals around the IAC motor at the back of the intake you can check as well for air leaks. They seem to commonly shrink up and leak.
Charles
 

·
Premium Member
Joined
·
27,375 Posts
Is this car 5-speed or A/T?
 

·
Registered
Joined
·
11 Posts
Discussion Starter #8
I should mention the client picked up this afternoon. I tried to hang on to it saying "I got on this great Alfa board and got some leads to try!" Perhaps she'll bring it back...

But for the sake of discussion... It's an A/T. One of the first things I did was to connect a fuel pressure gauge to observe characteristics when the car acted up. The pressure, though, was steady. Only nudging the needle when the car would act up. This being why I went down the O2 route. The CEL was either burned out or unplugged so it was not something I could rely on.

Michael
 

·
Premium Member
Joined
·
27,375 Posts
So did you give her the link to this www.alfabb.com ?

So you are saying CEL didn't even come on with rest of icon lights when key turned on during self-test mode?
 

·
Registered
Joined
·
3,506 Posts
The Air Flow Meter (AFM) hose, the black corrugated item, can be stressed by motor motion if the motor mounts are impaired. A very common failure is the dogbone mount at upper right rear corner of the engine compartment. One or both of the rubber bushings can be failed, allowing too much torque-related engine travel. This tends to break the relatively fragile and expensive right front motor mount under the A/C compressor. The combination will allow excessive motion and stress on the AFM hose, which -can- slip off and back on if the clamps are not tight. I've seen this on one of our AT cars. Eventually it will cause the hose to break. A break in the valley of a corrugation can be elusive. It does no harm, in my opinion, to sleeve the corrugations with a portion of a rubber inner tube, especially as a diagnostic test. It is not easy to cover the whole thing because of the ports for idle air controller and oil vapor separator, but the corrugations can certainly be covered. Shoe Goo makes a great sealant if needed at the ends of the corrugations, but other techniques may be more to your taste.

I've can't personally recall having any "bucking" other than caused by motor mount stress on the AFM and by cracks in the AFM hose. It has exactly the same symptoms you describe.

Michael
 

·
Registered
Joined
·
11 Posts
Discussion Starter #11
I will definitely give her this website address if I can. That'd be great.

No Steve, the CEL never did come on. Ever. I tried and tried. I know it must be either unplugged or burned out, but didn't have the chance to R&I the cluster to correct it. I have a feeling that one of her previous mechanics just unplugged it so that she and the car wouldn't come back. I'm going to see if I can get a hold of her and have a chat with her about it.

Brake cleaner is the quickest way for us to check for leaks in hoses like that. As it can be sprayed very fine and gets sucked in very easily changing the idle. I did a pretty thorough visual inspecition, though I didn't completely remove it and checked it running with brake cleaner to see if there were any changes and there were none. I'll tell you what, Mr. T, this was some violent stuff as the car would quit running and then start again (or try and quit and try...etc). When it would die, though, the dash lights didn't come on, not even the alternator light. Usually, if the car dies or even sputters and tries to die, the battery light will come on at least, but in this case, it did not. That is another reason I (we) were coming to a point of going down this path of O2sensor/fuel starvation thing. The more you beat on it to get it to act up, the more it would do it and the early in the rev band it would occur. Makes sense as it seems it would be leaning out, then as the lean condition would encourage higher combustion temps, it would happen earlier. The car would get really angry. It would not actually die. Just on acceleration at 4,000-4,500 rpms... BLAAAAAAHHHH, *BUCK,BUCK*, brrrrrrr, *BUCK*, BLAH!, *BUCK*, brrrrr, *BUCK*, BLAH!, brrrrr, *BUCK, BUCK*...

Well, hopefully, I'll get another whack at it in the not-to-distant future. Y'all are a great lot. We don't have NEAR enough Alfas down here and when they do come out, it's with the Ferrari, Lancia, and Fiat folks, seems like. This was an excersise in frustration and it's too bad I didn't find this site a couple of weeks sooner.

Michael
 

·
Premium Member
Joined
·
27,375 Posts
When you get one somebody else has "messed" with you are at a loss to base line it sometimes.

If CEL didn't light off did other almost "77" icons in speedo cluster light up when key turned on?

Running and bucking then engine dieing and no lights coming on usually points towards a bad ignition switch if lights normally come on when key turned on.
 

·
Registered
Joined
·
3,506 Posts
Or maybe a bad master relay or wiring appertaining thereunto?

(I'm feeling really, really tired just now and I think the anti-backflow valve to my brain is leaking.)
 

·
Registered
Joined
·
11 Posts
Discussion Starter #14
Yes, all the rest of the idiot lights worked. The reason I didn't pursue the ignition is because the problem is consistent and I assumed an ignition problem would be more erratic, ie hitting bumps or swinging keys. Interesting to continue discussing the situation with you.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #16
Fuel pump was my second thing (after the coil). Short of having a spec to know what fuel pressure should be, I couldn't know one way or the other. But what I could deduce from that was that it acted the same whether it was acting up or not, sooooo *shrug*.
 

·
Registered
Joined
·
3,506 Posts
Idle fuel pressure 34-36 PSIG, as I recall, with another few psig if you disconnect the pressure reference from the intake plenum. This can be useful to increase fuel pressure as part of a fuel starvation test. The fuel rail pressure is regulated to give constant pressure above the plenum pressure so that the absolute fuel flow depends as much as possible -only- upon the injector duration. I forget where this info comes from, but I think it's about the same as the LJet spec.

I think there is a spec on fuel flow through the regulator, too (pump volume). You measure it by hooking a tube to the pressure regulator return outlet and catching the return flow in a bottle. Some specific volume should show up in your bottle every minute, but I don't remember it just now. It should be a good test for the split in-tank hose, as the pump flow would be seriously reduced by any split even before it got big enough to reduce the fuel pressure.

Michael
 

·
Registered
Joined
·
2,639 Posts
Plug wires.
Paul
 

·
Registered
Joined
·
11 Posts
Discussion Starter #19
If memory serves, hers was ~2.5-3 bar so that converts out to what you've said (26-43psi). Very interesting.

Paul, nice sig. LOL! I checked plug wires right off the bat. The plug wires measured 1.5KOhms-2KOhms. The coil wire, however, measured out to 1KOhm. All out of spec according to the book I had, but still, not the culprit, I think.

M
 

·
Registered
Joined
·
11 Posts
Discussion Starter #20
Y'all are a helpful bunch! Very much like on the Guzzi boards I'm on. About makes me want to give up my clean '80 450SEL (90K) and get a GTV or an Alfetta. Unfortunately, I've taken up all the space I can in the garage with my projects so I'd have to give something up and it won't be my Guzzi, I can assure you. Gotta have some Italian machinery somewhere. :)

Michael
 
1 - 20 of 20 Posts
Top