rnoswal

I have seen some sources for the PROM in my ECM. Hypertech, around $145.00. A street performance chip it says. The usual performance enhancers but no reviews. Another is from Zip Corvette, stock replacement. No mention of enhancements, just the stock factory settings. Summit offeres a hypertech but no option as to the trans type. $170.00 and $60.00 core from Zip Corvette. I thought these were only a onetime use item. EPROMS can be rewritten but didn't think PROM's could be. I have read that revisions have been made to PROM's over the years but I don't think the one used for the 1984 Corvette would have many if any. But the Hypertech would have updates because if it being a more recently made PROM, maybe?

Price isn't a deal breaker but looking more for a replacement and if anyone has any experience with either or has suggestions from other sources. I don't need the enhancements actually, who will notice a supposed barely quicker time in the quarter with an 84! I would like it to be able to get a better fuel ratio if possible. The o2 sensor should be the thing that corrects that, If the originals were set either lean or rich from the factory that is. And again, its a completely different fuel system from 85 on up.

Sorry to ramble. I did send off the ECM to get it checked out and it checked out fine from DAvies Corvette.

Thanks

Russ

Kevova

I wouldn't invest in prom for a stock l83. Increasing fuel pressure to 15 psi. Crossfire could have been better, but it was a short term solution while they worked on MPFI. Porting lower intake. Less restrictive exhaust. Better heads. PcmofNC can make you something custom

rnoswal

Of course I understand about the other performance parts for this engine. Much could be done, like getting an 85 or better ;-). My focus is with an idle problem. It is in the spray pattern of the injectors at idle. I get a good cone pattern with both but every second or so I am getting more than droplets. It is a line of solid fuel shaped in a wave in that spray pattern. When that happens, the engine sputters, runs rough. The injectors are new, front and rear. The pigtails to the injectors are new. I had the ECM sent out and tested but there is still an issue with the spray pattern looking at it with the strobe of a timing light. That is why I have been trying to find out what pulses the injectors at idle. The PROM seems to be the last part to replace.

Like I mentioned. Performance isn't the issue. I could build a better engine but I want to make this work. It drives fine, accelerates pretty good, no stumbles or hesitation. It is sitting at a stop light and feeling that the engine is about to die. It never quite dies but it should be a smooth idle. If it was carburetted, I could fix it with a mixture adjustment but injectors are controlled by something else. There is no crank wheel so somehow it is firing with the distributor but the pulse length seems to be adjusted by the sensors that get fed into the ECM/PROM with set parameters with mixture. That is what I am trying to fix. Even if the prom isn't the problem, it is the last part of engine management I haven't replaced.

I hate throwing parts at it but there is no way to watch the patterns of firing and injectors on any diagnostic tool. I was just hoping some out there had experience with these different chips and can tell if the hypertech is necessary or even works on an unmodified engine. Should I go stock instead. Was just curious because of pricing of the few PROMs I have to choose from.

thanks

Russ

zachaeous

I purchased a hypertech chip on the forum from a member when I thought my stock one was bad. It turned out my ECM was the problem. I put the hypertech chip in the new ECM to see if I could tell any difference. I found that the engine ran worse with the hypertech chip than with the stock one. I would not pay that much for the hypertech chip. I would advertise in the for sale section here for a stock one and see what comes up.
I think the aftermarket proms for the 84 are more or less snake oil IMHO.

Kevova

FSM or a GM TBI training book would have principles operation FSM canbe found on eBay, Training manuals are harder to find; used book sites and thrift stores. Allen published a scope pattern book that is very informative related to ignition, sensor input and ECM output diagnosis.
Oscilloscope will show patterns, multiple trace will allow viewing of sensors and outputs.Dual trace is most common, I have seen up 6, but screen gets "busy" unless you have large screen. Datalogger programs allow multiple feilds of data.

rnoswal

Thanks. I always thought so too but never tried one because of that doubt. I will try the for sale ads. Thanks for your reply.

Russ

rnoswal

You are right. Getting all the knowledge you can about anything is best. If there was a shop around here that specialized and had the older equipment I would go there. It would take me too long to "go to school" with this car on the engine management side. Its one I will drive for a while but will eventually be sold. Gotta have a good running car to sell though. If there was only someone who knew what part of the ECM was used in the actual firing process of the injectors or driven by the pulses of the ignition. What opens and closes the injector, the mixture settings and such. And I am in the local corvette club, lots of members actually, small town but I am the only one with a 1984 crossfire engine! It could be the injectors "hanging up", not closing fully every 4 or 5 pulses (my guesstimate). They don't leak if I power the fuel pump on with around 15 lbs of pressure either.

So close but so frustratingly far. I will buy a stock PROM chip and see. That would take about everything out of the equation. Unless I bought 2 bad injectors. I got them new from Summit racing, front and rears, not remans but new for only 50 buck each. I see them go for almost triple that with some Corvette suppliers. Maybe that is why?

Thanks though. If I wasn't 67 and had an electronics type understanding, I would try what you suggested.

Russ