I have a 1987 Corvette with a replaced engine. It have the 1991 heads, a replaced (hot) cam and forged pistons. It runs well. There is about 10K on the engine. One of the nuts that holds the rocker arm worked loose and rotated off the valve/push rod. This was not immediately obvious to me so I took it to a shop.

The younger guys seem to be very computer oriented. They missed the rocker arm, and did a compression check. They gave it back to me ("you need to replace the head"). I opened it up, found the rocker arm, replaced the nut and realigned it. Runs well again.

At first there were no codes (the engine light was not on) but during all this the check engine light came on. The codes seem confused, but MAF and a miss in the distributor are consistant. The MAF was low, then high. The shop suggests a bad ground in the distributor. The car runs very well. They failed to fix any of it and gave up.

The computer also seems (acording to the shop) hard to read. I do not know if this is a 1) wiring issue, a 2) bad computer or 3) both the MAF and Distributor went bad.

The shop has given up. I know a better, better shop that I will drop the car off tonight.

If it is a replacement computer – is there an upgrade?? Is there a cheap way to get a good computer??

MAF seems to be a $200 "hurt me" - any ideas?

If it is a distributor– is there an upgrade?? If I have this one rebuilt – any specific changes I should ask for??

Any other ideas?? I think it may be just a wiring or ground problem, but who knows.

Thanks

 

Like anything here, if money is no object, you can upgrade your ECM to whatever you want. I would go to a good parts warehouse and get a reman ECM and be done with that. It could be the EPROM too. Not sure about your year but I have an EPROM in my 91.

As to the distributor, you can replace it with a small coil one. I believe the favorite here is the MSD (My Spark Died ) 8366, IIRC.

I'd get a can of MAF cleaner. It comes in a spray can and BE GENTLE and spray a mist at the filaments or you are buying a new unit. Try that first.

 

The miss could simply be a bad plug wire, especially if it is a consistent miss.

So what check engine codes did the shop find? With a code and a Factory Shop Manual any decent shop should be able to diagnose the problem. I suggest you get your hands on a shop manual. You'll be amazed what you can do on your own. It will pay for itself the first time you use it.

The 87 ECM does not need to be upgraded. The codes are very easy to read if you know how. You can read them with nothing more than a paper clip.

The distributor does not need to be upgraded either. It's just another place where you can spend money with no improvement to performance.

 

Pull the codes yourself
http://www.corvettephotographs.com/ecm.html

and work through the diagnostics flowchart to identify a problem

http://www.chevythunder.com/Flow%20c...0Chart%20Pages

before wasting $$ with mechanics that are younger than your car

Be aware however,
a code refers to a problem somewhere within that whole system ,not just that the system item is faulty.
Could be wiring , a short, bad connection or ground problem ( very common with age in these cars)

 

And vacuum leaks

 

You have to remember, The ECM on ANY OBD-I system is only telling you what has been effected, NOT what is wrong. THAT is totally up to you to interpret and sort out the issues..

Later OBD-II systems are more able to point right at the fault, but you;re not going to ever see that on your '87....you do not have the harness, or most of the sensors and support for that late model system. It would be cheaper to buy a car than it would be to buy the nervous system from one... Don't blame the zip farmers too much. They go buy what the local trade schools teach. There are none offering courses in ancient technologies...that I'm aware of. For that, you just have to put up with some old fart thats been down that road a few times...

There IS a later model ECM that is designed to make your "batch fired" injection into a seqencial multiport EFI BUT, the gains are minimal, (less than 10hp) and its a big expense. Do a search for OBD upgrades if thats interesting.

 

This isn't particularly true. OBD2 systems will still only generate a list of fault codes. The advantage to OBD2 is that the system generates a fault code from a more extensive, more complete, standard universal list:
http://www.obd-codes.com/trouble_codes/

OBD2 still won't tell you why any of those things is happening.

 

Go back to the start, you had a rocker come off. It may be a fouled plug.

 

IF you decide to swap out the ECM

DO NOT let your EPROM chip go with the old unit!!!!!

Make sure you replace the original EPROM into the reman'd ECM.
If you don't, and loose the factory EPROM you will hard pressed to find a replacement unless you go with custom tune.

 

Nothing wrong with the 87 ECM it is faster than an 85 ecm.

You have an intermittent issue, most likely a bad earth.
Check your earth wiring, there is a few connected on the driver side above the oil filter into the block access from the side (there is a flat braided wire to the frame that goes there also).
There are more earth wires on the transmission bell housing (on the driver side at the 10 pm position where the tach filter is located)

Note over tightening the valve lash can cause a miss and loss of compression, factory lash is one turn extra from zero lash. (where you can no longer rotate the pushrod, when that cylinder is on top dead center) My aftermarket lifters only need 1/4 turn extra.

Check your plugs, then leads measure the leads resistance with a multimeter. I also had a problem with an injector connector, they can break when you remove the plug from injector by the leads.
Easy way to check is start the car from cold, run for 30 secs and turn off. Then check exhaust header an inch from heads that they are all the same temperature, if there is a cold one check that injector/replace the injector connector.

The distributor coil and can be checked as per service manual, also the distributor module can fail that could be related to temperature.

If you have not yet got a Field Service Manual get one asap

http://www.ebay.com/itm/1987-Chevrol...item5d34f0807d

Good luck

 

Or maybe the guy who worked on the heads reused the nuts. They are one use only, and numnuts goofed up

 

So I now knw what is wrong with my car. The tech guys tell me the resistance in the electrical part of the distributor increased and burnt out the computer. I need a new computer and distributor. Also the MAF is open (needs replacement) – an unrelated, but also unwelcome “hurt me”, I am not ever happy to spend money, but the way this is going, I can see price differences (making me focus on money) but not quality differences (where I want to be - one and done forever).

Sooo on the computer. CarQuest wants $89, O’Reilly $79, AutoZone $79 and Napa $129. All are Cardone remanufactured – I think there is no difference in these. Price is easy, but quality is harder to see with these guys. Is there a better quality ECM???? Do I need a better quality ECM?? Maybe the price is the only thing that is changing here???

On the distributor I have the same issue with more confusing variations and warranty differences. Cardone is still everywhere and there is generally one more cheaper with a shorter 1 year warranty (Cardone is a lifetime) CarQuest wants $155, O’Reilly $133, AutoZone $125 and Napa $134. All are Cardone remanufactured, but in this case there are some cheaper "Accel" stuff out there and there are a few $300-500 deals - This is a “grocery getter”. I want reliability over preformance – any better better distributors ideas?

The last one is the MAF – Duralast is $150, Napa $154, and carquest has a new one for $285 or reman for $186. In this case there are no 2 brand names the same. So the quality of any of these is ... unknown. Same question, what is the purchase I can make that gives me no problems for years???

Basically, with no quality information, it turns into a price only game. I think that may be too simple. Any ideas???

 

Before you spend 1 dime on the MAF....make the "techs" install a new MAF power relay.

These shop guys today see the problems and not the cause. More MAFs have been thrown away over a $7 relay than ANY other elect part on a car. When the Power relay fails, and they do often, the MAF is dead as a door-nail and can show open or no signal. May as well buy 2 relays and swap out the burn-off as well...its next to the power relay and the wrong one gets changed too often.

ECMs.....buy from whoever has the best return policy. Since they ALL come from the same mfg, rebuilder, buy from the guy that will be customer friendly in case there are issues with the unit. SAVE your PROM ! ! Believe it or not, its harder to find a good stock PROM than it is an aftermarket POS. If you get jammed up on that, let me know, I have 3 or 4 for 87 coupe/auto z51.

Dizzy.....check your local speed shops. The HEI dist is a very reliable unit and there are LOTS of options from many mfgs. MY local speed dealer (Comp Sales) had a complete small cap, the whole enchilada ready to drop in, ICM, cap, rotor,everything, for $88 a few months back. I like the small cap option since it gives you a little more access to other things back there...vac lines, oil press fittings, wire harness etc..
Whatever you do, do NOT spend more than $125 on a replacement HEI distributor. They are too common for a reason. They work and everybody makes one.

The theory of the dist building resistance and burning the ECM is a little "iffy" to me....resistance comes from many places in the system and the potential has always been there. The system has built in protection from most of this. What is MORE likely to have happened is someone shorting a HOT-wire during some testing and frying the ECM. These things are a lot more durable then people think. Most damage comes from vibration having cracked a board, or someone back-feeding power someplace that it does not belong. In any case, if its damaged its toast. I'd swap with a known good unit to confirm. ECMs are also supplied with their power as well as ALL under hood eng mngt systems from fusable links under the battery. These originate on the jumper pole. The ECM ground is one of the famous 5 on the block near the oil filter. Either being loose or dirty will cause misfiring and/or a no-run condition.

If I sound like I question these shop guys when they diagnose a 25 yr old car and its 30 yr old technology, its because I DO. This system is older than many of the kids that work on the car and they simply do not understand how it is and how it works. They were brought up on "plug & play" systems that are modular...ID the defect and swap in a new part...done. The C4 with the OBD-I takes a little more finesse to know for sure. Way too much throwing parts at C4s to solve problems....like the MAF. Lots of those sold when it was just a relay.

Good luck with getting it back on the road.

 

Thanks - Got it

On the 25 year old. I switched shops and used the 45 year old. I think he was a little fussy about part quality (wants OEM from Chevy at $800 vs $400 from the corner parts store). So I am sure about the ECM and Distributor

For $7 I think I will wait on the MAF and go with your advice (I am happy with all of it really).

So the only difference is the small cap is size? What is that proformance shop with the $8x deal? If he is in San Diego - I think I am there

thanks

 

Fussy 45 year old, methinks he is getting a kick back. I absolutely agree with leesvet about both the ECM and the MAF relays. Believe what you have been told about the "chip" a new one is amlost impossible to find. Why do you want to replace your distributor? About all that can and does go wrong is the Ignition Control Module which is not costly and can be changed by a quasi trained monkey. Back to the ECM, that 165 ECM was used extensively in the 86-91 period. Any one will work just fine in your Corvette WITH your "chip". The ECM in my highly modified 85 came from a 4 cylinder S10.

 

Yessir...

the small cap vs large cap...no meaningful difference in performance that I know of...its just smaller by quite a bit. The wires on top will be more crowded but the overall size is much smaller and that allows you to have some working room back there..

That "sale" was a while back...but they might still have a good deal available...
Its "Competition Sales"on North freeway in Houston,. They will sell & ship. Look them up and ask if they have a GM HEI small cap dist complete for your 87 L98 vette. Never hurts to ask. When I saw the display there was a stack of boxes....with the sign promoting the $88 unit. Who knows..there may be some left over. They had a pile of 'em back then.

 

That makes no sense, so either your tech guys don't know what they are doing or they didn't do a good job of explaining to you what the problem(s) is.

The ICM (Ignition Control Module) in the distributor sends DRPs (Distributor Reference Pulses) to the ECM. The ECM uses those pulses to synchronize the firing of the injectors with the rotation of the engine. The ECM sends timing information (spark advance) back to the ICM. These are electronic signals and there is no "resistance" involved.

Possible problems in the distributor are the previously mentioned ICM, the capacitor, the pickup coil and the spark coil. All of these things are easily replaced (well, not the pickup coil -- you need to take the distributor out to replace that) so there is no point in buying a new or remanufactured distributor. You can get your ICM tested at most auto parts stores. I have heard of pickup coils breaking into pieces but mine is just fine after 27 years.

The difference between the small cap distributor and the large cap distributor is that the large cap distributor has the spark coil inside the cap and the small cap distributor has the spark coil located outside the distributor. The factory used to mount them on the intake manifold (no room for that with fuel injection) and aftermarket units are mounted on the firewall, so you'd have to find a place to put it if you go that route. I see no benefit to the small cap distributor myself, but that's my opinion.

The HEI distributors are very robust and reliable. They are in literally millions of cars. Most aftermarket units are actually GM HEI units that are modified, usually by changing the spark coil. The stock configuration is quite capable of firing your plugs under all conditions (even with modified engines), so there is no need to "upgrade" it.

Your car will run just fine with the MAF disconnected. Try that and see if there are any big changes in the way it runs. Substituting a known good MAF is much better than buying one because it MIGHT be bad.