MAF sensor question

[KDirk]

Ok,

I am in the process of trying to fix the rough idle/stall problem I am getting with the 88. I am wondering, is the MAF sensor on the 91 the same as the 88 electrically? I am tempted to swap them if the MAF is identical, to rule that out (or in as the case may be) as the cause. Has recently had a full tuneup (including conversion to Delco ICM and coils, O2 sensor, plugs, wires, TB and MAF cleaning) and a new IAC motor. Have also replaced every piece of rubber vacuum line I can find under the hood.

So far, I have eliminated a fuel and ignition problem, as all components of those systems check good. This leaves only three possibilities:

1) MAF sensor (this seems to be ok, reads normal in diganostics)
2) intake manifold gasket leak - suspect leak (doing gasket job today)
3) partially blocked cat (seems the least likely problem though)

In the event that replacing the intake manifold gasket does not solve it, the MAF is the next easiest to check (assuming I can swap the one on my 91 to the 88 and it will work correctly) and if that doesn't pan out, I am left to check the exhaust back pressure to see if the cat is blocked. If none of that is a cure, I will probably cuss a blue streak and let the car sit for a week while I take some time to think of what to check next.

FWIW, the car accelerates normally and runs fine at load (though fuel economy is not great) but "hunts" at idle, and if left idling long enough (15-20 seconds with engine hot), will stall out and die. It will restart immediately with no problem, just can't keep it running.

I will be inspecting the injectors while the rail is out doing the manifold gasket to be sure they are all firing well, but the injector load balance test bears out that all 6 are delivering fuel. I suppose I could have leaky injector(s) causing this problem, but it seems more like a vacuum/air/exhaust problem the way it is behaving.

KDirk

[Mc_Reatta]

The MAFs are supposedly not identical, so while they may swap mechanically, they should not perform quite correctly 88-90 vs 91.

Do you have access to an O-scope to look at the output?

If your problem is associated with heat, it and the ICM are likely candidates as they have lots of semiconductors inside.

[KDirk]

MC-

Have a known good (tested) ICM on the car, and a good spare on hand. I do have a scope, and so I may test the output that way. I figured there was just enough difference between the 88 and 91 engines to dictate a change in the MAF, but thought I would ask anyway.

Does not seem like a thermal issue, the symptom is present on both cold and hot engine.

KDirk

[89 Maui]

KDIRK -

Seeing that you did the tune-up & 02, but still rough idle. Do you have a E026 code current or in history? The EGR can trigger a E026 code. The best way to check the EGR valve is to turn the ignition sw ON but engine not running, then go into diagnostics and go to ECM outputs, enter YES until you come to EGR solenoid #1. With the hood open you should hear the solenoid "click" on and off. If it clicks that solenoid is good. Then in diagnostics enter YES and EGR solenoid #2 will start "clicking on & off. Then EGR valve #3.

If any of these solenoids do not "click" then replace you EGR, it can cause your engine to run rough at idle.

I just replaced mine and the engine now runs smoothly at idle.

[Mc_Reatta]

I think you might try swapping the MAFs just for grins. I would think the 91 would be tweaked slightly for the improved intake, but I would expect a bigger change in the PCM software than the hardware.

As they are both fused at 10 amps and work on a 5 volt reference signal you shouldn't suffer any electrical problems by switching them.

If your mostly interested with performance at idle, I don't expect there to be much difference in their signal outputs at closed throttle . I would expect the different performances between the two to grow as air flow increases, but that's not where your problem lies.

Otherwise just hook up the scope and monitor the frequency of the MAF output as it idles. Shouldn't change much as the only change in airflow would be from the IAC modifying the air thru the butterfly bypass. If the output fluctuates just as the engine starts to stumble before it dies then you have your culprit.

Padgett kindly shared a photo of what it should look like in post #53 of this thread:

Strange behavior

[wws944]

Kevin, does the problem happen when the engine is cold? Or just when hot?

[KDirk]

Ok,

To address the last few queries:

No E026 (or any other) codes set. The EGR is good, I had previously verified all 3 solenoids in diagnostics as Woody described. Symptom is present at either hot or cold engine, open or closed loop mode. After getting the whole thing torn apart yesterday, I found the EGR gasket was questionable, the intake manifold gasket was shot and the PCV valve grommets at both the intake and left (front) valve cover were in pretty sorry shape (LOTS of oil blow by).

When complete, I will have new intake manifold, valve cover, EGR and EGR adaptor gaskets, new EGR pipe gasket, new upper and lower radiator hoses, new heater bypass hose, T-stat and new injector O-rings when done.

I will be finishing the reassembly today (have the intake and valve covers back on with new gaskets) as I still need to reinstall the throttle body, MAF housing, thermostat housing and the alternator/bracket and put new coolant in. Got cut short last night by a rain storm that moved in as I was working on it, so had to close up shop early.

Once that is all done and I have run a test drive, I can better say what still needs to be checked if I am still having problems. I hope - probably foolishly - that the new gaskets will solve the problem since I suspect I had at leak on the intake manifold at least. After seeing the EGR gasket, there may have been an issue there as well based on the appearance of it. Yet, I am just cynical enough to know it won't be that simple.

I will say the intake and surrounding area was a filthy mess due to oil leakage from the valve cover gaskets and PCV grommets leaking. A lot of time was spent cleaning with de-greaser and a stiff brush.

KDirk

[2seater]

If the '91 has the tuned port style manifold (it should), the MAF sensor is different and will not fit in the '88 casting, even though they are externally identical. The frequency range is also identical. 1991 sensor on the right.

[Mc_Reatta]

Thanks 2seater for answering the question about swapping the MAFs.

Kevin, if your gasket replacements don't do the trick I guess you'll have to get out your O-scope.

[Corvanti]

i'm betting on the vacuum leak - either the intake manifold gasket or a unseen rubber hose/connection leak.

if there is still a problem after repairs, i used "carb spray" on everything that could have carried a vacuum on my "old" cars... if the idle increased, then that was the location of the leak. bonus: it cleaned greasy/oily things up.

just throwing it out there!

[KDirk]

Corvanti-

You win that bet. I got the car back together late this evening and gave it a test run. It is running like a brand new car for the first time since I've owned it. On an extended highway run at 65 MPH, my BLM was dead on 128, and my Fuel Integrator reading was running between 125 and 132, so right on spec. Previously they were both high.

I cannot believe how much better it runs now, it is like a different car. It looks like the intake manifold gasket was the major culprit, but it's likely the EGR valve gasket was also shot. When I took it off yesterday, there were sooty marks that crossed the barriers in the gasket between chambers of the EGR valve. So, it looks like it wasn't sealing tight either.

The best part is that all the gaskets and hoses from the intake on up are now all new so there are no oil or coolant leaks and the entire upper half of the engine is spotless for the first time since it left the factory. It looks so much better now than it did 2 days ago.

I will add that getting new PCV gaskets for the intake and the left (front) valve cover that fit right was a real job. I ended up finding them in a Dorman assortment pack for (yeah here comes some dirty words) Honda/Acura. The ones the computer listed as being specifically for the 1988 3800 VIN C Reatta were both much to large to fit right. Even the ones I used were extremely tight, but that is good since it will do a better job preventing oil blow out.

So now the car is about 100% mechanically solid. Ought to do cradle bushings as a preventive item before the end of the year (mostly for my own piece of mind - they aren't bad) and might do suspension next year (it is ok, but the age of the original parts concerns me). Everything else I need to do is cosmetic work (front door speaker grille recovering, replacing some minor interior plastics, repainting top of dash pad due to sunlight fading, finish fixing drivers side 16 way seat switch pod) and then the car is pretty much show ready.

For anyone who will be attending the Heartland Regional in Earth City, MO in September, I will plan to be there with at least the 88, and probably will bring along the 91 also if I can find someone to come with me as a second driver. I hope we can get a decent number of Reattae at that event.

KDirk

[Ronnie]

... I will add that getting new PCV gaskets for the intake and the left (front) valve cover that fit right was a real job. I ended up finding them in a Dorman assortment pack for (yeah here comes some dirty words) Honda/Acura. The ones the computer listed as being specifically for the 1988 3800 VIN C Reatta were both much to large to fit right. Even the ones I used were extremely tight, but that is good since it will do a better job preventing oil blow out...
KDirk

Glad to hear your problem was solved!

The PCV grommet that I have in The Reatta Store is listed below. Is it the same part # you tried to use that didn't fit?

ACDelco CV5003C PCV Valve Grommet
$7.60
1988-90 PVC VALVE GROMMET

[KDirk]

Ronnie,

That grommet is not the one I bought (it was a card packaged one from Dorman - HELP! brand - so aftermarket not Delco) however the one in the picture at the link you provided looks exactly the same as the valve cover PCV grommet I bought in terms of size. The one I had definitely is not correct for that application.

The funny thing is that I did get it to work as the intake manifold grommet (the one the PCV valve plugs into). The one I used as the valve cover grommet came out of a Dorman assortment pack marked for Honda/Acura vehicles. There were 6 different grommets on that pack, it happened to have one that worked perfect.

So, to summarize:

- The intake PCV grommet I was originally sold (Dorman HELP! brand) and cross referenced by the computer at both Advance Auto and O'Reilly, cannot be used as it is much to large in diameter to be snapped into the PCV hole on the intake.

- The valve cover PCV grommet (Dorman HELP!, also cross ref'd at both stores by computer) is too large for the valve cover hole. I did use this one for the intake instead, but it was still a very tight fit.

- I had to use a grommet from a Dorman HELP! assortment pack for Honda/Acura vehicles as it was the only one I could find that would fit the ID of the hole in the valve cover, and still accommodate the metal tube that needs to be inserted.

A real challenge to get right (trips to two auto parts stores, and visually verifying the fitment vs. the original grommets I had removed) but got it right at last. I'd suggest anyone doing intake/valve cover gaskets do these grommets as well. They are very bad about leaking oil after the harden up from age.


KDirk

[Ronnie]

Thanks Kevin, The reason I asked is because someone has bought one of the Delco grommets from The Reatta Store recently and I though it might have been you. I've not received any feedback from the person who bought it but that doesn't mean that it fit properly. I hope that it did. I don't want anything listed in The Reatta Store that won't fit if I can avoid it.

[KDirk]

Ronnie,

No problem. I would've ordered in the store if I had the foresight to order them about a week ago. Those two grommets were not on my radar when I planned this project, and most of the other parts were on hand as I got them "free" in payment for a favor I did for a local parts distributor I've dealt with for years.

I will plan on getting the next round of parts from "the store". Maybe some suspension parts will be on the list.

KDirk