Question about prom vs ecm?
Thread Starter
Racer
Joined: Jun 2001
Posts: 377
Likes: 10
From: Chicago IL
Question about prom vs ecm?
Sorry for a basic question, but could someone explain the function of each? I am trying to solve a hard start when warm problem and have been told it could be the ecm (I will try to diagnose this weekend). Given that there is a prom (chip) in the ecm that controls fuel ratios, is this what I would really want to replace, or am I really replacing the ecm (the box that houses the prom)? Or…. When using the term ecm, am I really talking about the module/prom combination? Thanks.
Pro
Joined: Sep 2001
Posts: 542
Likes: 1
From: Stuck in the 80's
In a nutshell, the ECM is the computer and the PROM is the code that is specific to your car. When you have to replace your ECM, you need to remove your PROM from your old ECM and put it in your new ECM.
When people burn their own chips they are changing the data on the PROM.
What kind of hard starting problems are you having?
When people burn their own chips they are changing the data on the PROM.
What kind of hard starting problems are you having?
Thread Starter
Racer
Joined: Jun 2001
Posts: 377
Likes: 10
From: Chicago IL
Thanks, the car starts fine when cold and fine just after shut off. But, if you drive and let it sit for a few hours and then try to start, long embarassing cranking - I have owned the car since 88 and have always had the problem. Out of normal maintenance, I have recently replaced the rotor, cap, wires, plugs and injectors - same condition. From what I know from the tech forum, it could only be a couple of remaining things: ecm, cts, or some other issue with fuel pressure. I am going to check fuel pressure and try to get a cable to scan the ecm readings (dont know what I'm looking at yet). I would love to solve this finally so any suggestions are appreciated.
Thread Starter
Racer
Joined: Jun 2001
Posts: 377
Likes: 10
From: Chicago IL
no codes that I know about, unless codes are set without the check engine light. I didn't check maf relays because the car is running fine otherwise - (except a good deal of pinging with 87 gas on acceleration). Are these relays a source for a hard warm start? I had a theory that the MAT sensor was getting heat soaked in this condition, but other forum members mentioned that the mat sensor has no real role in startup. My other theory is that the cts is sending a false high reading (or the ecm is seeing a false high reading) and I am getting a lean condition during the warm start.
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
Originally Posted by viii
Thanks, the car starts fine when cold and fine just after shut off. But, if you drive and let it sit for a few hours and then try to start, long embarassing cranking - I have owned the car since 88 and have always had the problem.
Also, the 85 has no MAF relays, it has a MAS module that does what the 2 MAF relays do.
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Intermediate
Joined: Apr 2002
Posts: 49
Likes: 0
From: albuquerque nm
Response
Had the same problem. It turned out to be my fuel pump. Check your fuel presure. Also your fuel filter. On some models there was a recall on the fuel lines. Some came with a filter on the return line. If so replace both. Good luck
