Hard Starting Problem

RonnieH · 06-05-06, 01:49 PM

After winter storage, I have been facing an increasingly hard time getting the car to start. The Vette is a '90 (L98) with 28,000 miles. Initially, first time started in the morning, car fired right up. After sitting in the parking lot at work, took about 10-20 minutes to get it to start. I inititally thought it was a fuel supply problem, as sometimes the car would fire up and shut down after 1-2 seconds as if running out of gas. I also thought it somehow was heat related, since I only had the problem after car sat in the sun all day after starting o.k. in the cool garage in the A.M. I have replaced the fuel pump (thinking it was some type intermittent problem), fuel filter and tank filler cap. The problem has since worsened to the point I am no longer driving it.It is now hard to start all the time. I can drive it, put it in the garage and shut it off. Sometimes, it will start back up immediately and sometimes not. I am now thinking maybe fuel injector related. When the key is turned on, the system pumps up to 36-38 psi as it should. With the motor running, it runs around 42-44 psi. After shutting the engine off, the pressure starts dropping about 3-6 psi every 5-7 minutes. After 50 minutes, it is down to 6 psi (I have not blanked off the fuel return line to the tank). Once started, the car runs fine - no hesitation, missing, rough idle, etc. Questions: 1.Is this pressure drop typical or could it indicate a fuel injector problem? 2. I wanted to check the fuel injector resistance with an Ohm meter. How does the electrical connection disconnect from each injector? It was not obvious to me and I did not want to just jerk on the connector and create worse problems 3. Is there a good way to check the ECM to ensure it is operating properly? Speaking of the ECM, where would it be on a '90? The Hayes manual indicates it is on the firewall on the passenger side. I'm not sure what the ECM actually looks like, but I don't think it is there. On the driver's side is a rectangular box close to the firewall - it has a plastic top and held together by Velcro type material. Might this be it? I have also looked for external fuel leaks and vacuum leaks, but everything there seems fine. Any thoughts/suggestions would be greatly appreciated. If possible, I would like to avoid taking it to my local dealer. I have had my SUV and my wife's car in there for service and have had problems with them the last two times. One other thing - I have not noticed any codes. Just to be sure, I'm going to rig up a jumper wire and check for codes tonight to see if anything is stored in the code memory. One guy at work meant well and he told me to check the cold start linkage. After looking for about an hour, I verified the 90's do not have the cold start assembly. He still swears it does. I do remember reading somewhere the MAF has temperature tape or something like it which measures temp. of the airflow coming in and makes adjustments accordingly. If so, is there a good way to check this. Thanks again.

geogolf · 06-05-06, 02:22 PM

ron I will try to answer your ?s but no expert ecm is the retq. box above batt. to check ohms just pull clip off of inj. it sets in a grove, once you do one no prob. inj should read all the same or slightly + /- one or two ohms. since you have a 90 you dont have a maf our sys. is called speed dentisy do a search for hard starting and you will probally find answer to your problem did you change fuel filter that is first thing I would do hope this helps geo.

coyote4 · 06-05-06, 02:34 PM

I Had the same problem with my 89. I changed the MAF relays to a new spec and it went fine since then. Some dealers told me it was the injectors but a gm service report said it was the relays for the maf that didn't produce enough energy so the car would just fire up and die right away.

Robertwav1 · 06-06-06, 07:23 AM

Had the same problem on a 93, turned out the fuel pressure reg diaphragm was weeping.

RonnieH · 06-06-06, 09:49 AM

I checked the injectors last night with an Ohm meter and they appeared o.k. All the injectors measured 17.5-17.8 Ohms. I'll pick up an old spark plug on the way home and check for spark this evening. Just checking for spark won't be a definitive answer since the car at times starts up 1st time and sometimes 10 minutes later it starts. I have seen in previous threads there is some testing that can be done on the coil and distributor internals. Does anyone have a good link for checking out the coil?

RonnieH · 06-07-06, 10:15 AM

Checked for spark last night and it seems o.k. I'm thinking of checking out the Throttle Body Sensor next. Anyone have experience with this.? I read the spec. is 0.54 volts. If I check it tonight and it is off, is the current TBS adjustable? If so, can someone share with me how to adjust back to the proper range. I looked at the throttle plate previously, and it did not look particualry dirty, but I will clean that this evening as well. I was thinking of spraying some starter fluid into the intake. If the car fired right up after doing that, I'm thining that would be a good indicator of a TBS problem. Unless anyone can give me some other pointers, I'm pretty much out of ideas. There is a used car dealer in my area who specializes in Corvette resales. He has someone who does not work for him directly but does Vette repairs for him on an as need basis. If I'm not able to find anything wrong with the TBS sensor tonight, I may let him take a whack at it.

geogolf · 06-08-06, 10:20 AM

hey ron this probally is not the prob. but you might try to clean the the res. pellets on the side of you ign. key or try your spare key clean with alcohol or starting fluid geo.

RonnieH · 06-08-06, 10:40 AM

As a last resort yesterday, I did try the spare key w/o success, but thanks a bunch for the thought and reply. I think (and hope) I have narrowed the problem down to the TPS. The spec is supposed to be .54 volts. The actual reading is .74 volts. I squirted a little starting fluid down the throttle body and it started right up, which indicates to me the TPS is shutting off the gas flow. I cleaned the throttle body and throttle plate and plate sealing surface while I was in there. I am going to pick up a new TPS today if the dealer has one in stock and try and install it tonight. If it works, I'll post and let folks know in the event someone has similiar problem. Thanks to John Robinson - his post started me looking in this direction even though his symptoms were not exactly the same as mine - his vehicle actually shut down while driving it. Sharing his post actually helped me - hopefully my trials and tribulations will help someone else down the road.