1985 LB9
1986 ecm with 89 prom

Need a little help where to start on this.

Engine started and ran well but developed a strong miss. I found that one of my injectors was firing intermittently. Ordered and installed Bosch III's along with new fpr. While the plenum was off I changed the mat (because I was getting strange ambient temp readings) and the iac.
Engine runs and idles great, fuel pressure is good. Tps at .54 and iac set per instructions...But as the weather is getting colder here, it is getting harder and harder to start when cold. Warm starts are fine.

Should I start with putting the old iac back ?

 

IIRC, an 89 TPI had no cold start injector where as an 86 did. So, the 9th injector isn't being fired on a cold start. That may be the problem now that the weather is cooling off. Although, the newer PROM should be making up for that by lengthening injector pulse on cold starts. Somebody more experienced on a MAF system might be able to help more as what little I know is from my old Formy and current T/A both of which are(were) 92's, (SD's).

 

Tpi84

Try cycling the ignition key first. After setting over night, the fuel pressure is most likely 0, and the fuel pump prime on a very cold engine takes about 1 1/2 seconds to build up to normal pressure. Now, first time turn on the key and wait 2 seconds and don't try to start it yet. Then, turn the key off and wait 20 seconds. Then try to start the car. On my 1988 9 injector tpi system, it's a little picky when very cold.

Dave

 

I have had a fuel pressure gauge on it and it primes right away...pressure builds quickly.
It wants to start but just stumbles and stalls several times. I'm afraid that when it gets really cold I'm not going to get it started.
All my ignition parts are new also and worked fine prior to the fuel system upgrades.

 

Hey man,

I remember you responding to my thread about the same issue I had with my 85 and the Bosch III injectors. I dont know how easy it would be, but I would try finding a set of the 85-87 style injectors that are known-good and trying to run those.

When I re installed my original injectors, all hard starting problems that were caused by Bosch III went away.

 

i had this problem after i did my injectors, it was the ECM that went bad, the old injectors shorted it out, thus not telling the injectors to enrich the fuel mixture on a cold start which is the benefit of the 1989 setup deleting the cold start injector, also tryout the coolant temp sensor first though because its a lot cheaper it could be giving the ECM false readings

 

The engine runs so much better that I do not want to change the injectors.
I have 2 ecm's both do the same thing...coolant temp reading is very close to gauge reading..I'm thinking maybe it's the prom. It's a piggyback type that I got from tpi parts.