88 4L Renix cranking issue

[DaveVmax]

I'm betting on a bad mains cable, or the braided ground strap that runs from the head to the firewall.

i changed all the grounds.

i still need to replace the power cable

 

[DaveVmax]

CTS or MAT can be checked with a meter.

Double check the vacuum hose integrity from the TB to MAP, along with the electrical connection there.

ill check them tonight

 

[cruiser54]

ill check them tonight

Do that and replace the power cable with a larger gauge when you get a chance.

 

[bigalpha]

So the starter will turn the engine over but then the starter will bog down?

 

[DaveVmax]

So the starter will turn the engine over but then the starter will bog down?

yes exactly and it will do it 2 or 3 times before it actually starts running



this is the second starter in the truck and the old one did the same... (i thought it was a starter at first)

 

[Ecomike]

if i just have the battery and accessories on the pump will still be priming.

Sounds like a bad fuel pressure regulator to me!

 

[Ecomike]

The motor must spin ~300 RPMs before it generates enough current at the CPS for the Renix ECU to decide to start the motor. If the cold was keeping it from spinning that fast, yes, it would not start.

I have read and seen this 300 rpm a thousand and one times, but in recent tests with my 87 renix it started right up while barely turning over, in 3 second, rumph, nothing, rumph, nothing, runmph, vahroom that must have been about 3 rpm and .27 V on the CPS!

 

[Ecomike]

ok just wanted to update this...

i disconnected the battery and touched the - and + together for over a minute

connected and the truck runs PERFECT now starts perfectly drives great for the last 2 days...

does the computer need to re learn after you install a new ICM?

Crueser54, and others who keep arguing with me about Renix ECU memory, ARE YOU READING :read: THIS GUYS DATA???????

!!!1

It does something to some Renix ECU's, If it is not clearing some odd memory issues, it is still doing something!!!!!!

 

[Ecomike]

bump truck runs but has an intermittent cranking issue still..

it will crank then die as if the starter is giving out kicks it down and has barely enough power to get it going.

i dont think the power is getting cut from it because instantly its cranking again....but it will repeat this 2 or 3 times before it will run.. when it runs it runs perfect.

it will never do this on cold starts only after its been driven then parked and cranked again 5-10-15 minutes later.

im out of ideas?

can the manifold air temp sensor be involed? or 02 sensor?


dont say starter because its brand new.

I don't think they make new starters, rebuilt yes, and rebuilt starters can have problems!!!!!!

MAT, MAP and CTS sensors can cause temp related starting problems that flood the engine, or starve it for fuel. O2 sensor is not used while starting.

It is not clear what you are saying (this makes no sense: "it will crank then die as if the starter is giving out kicks it down and has barely enough power to get it going. ") about the hot engine cranking problem, but it sounds like a bad starter still, new or not! Or a dying ingnition switch or starter relay.

Also the fuel pump should not keep running as you mentioned earlier. Go to igniton run but do not crank, and if the fuel pump does not stop running in first 7 seconds, you have a wiring hack bypass, or bad wiring somewhere, or a stuck fuel pump relay!!!!

 

[Ecomike]

yes exactly and it will do it 2 or 3 times before it actually starts running



this is the second starter in the truck and the old one did the same... (i thought it was a starter at first)

Is it a new battery? If not, it could be the real starter problem. Batteries on their last legs, can work perfectly one second then not the next. Put that volt meter on the starter when it is acting up on the hot cranking, and see if the battery voltage is dropping way down or not when the cranking bogs down.

I had what seemed like a good battery, bad CPS, then a new CPS but low CPS voltage, which required moving the cps closer to the flexplate, followed by a sudden battery failure (in steps), that kept me going for 2 weeks, before the battery crashed enough to be obvious!

 

[cruiser54]

Is it a new battery? If not, it could be the real starter problem. Batteries on their last legs, can work perfectly one second then not the next. Put that volt meter on the starter when it is acting up on the hot cranking, and see if the battery voltage is dropping way down or not when the cranking bogs down.

I had what seemed like a good battery, bad CPS, then a new CPS but low CPS voltage, which required moving the cps closer to the flexplate, followed by a sudden battery failure (in steps), that kept me going for 2 weeks, before the battery crashed enough to be obvious!

Perhaps a battery load test is in order?

 

[DaveVmax]

might i add this is a fairly new optima blue top..

i had this in my 92 cherokee and it worked perfect.

 

[bigalpha]

Are the connections to the starter solid? Also, as mentioned earlier, the fuel pump shouldn't be running continuously. Go out and switch the relays around - cheap and quick test.

 

[Ecomike]

might i add this is a fairly new optima blue top..

i had this in my 92 cherokee and it worked perfect.

Fairly new = ?

Is it used daily, or does it sit for weeks between use?

There is small starter relay near the battery, rectangular shape relay with one large post and about 4 small posts that may be going bad.


Sounds like a hot load test at a parts store of the starter and battery might be a good idea.

 

[DaveVmax]

OK update here guys..

i pulled the fuel pump relay and the pump still turned on(to make sure i checked everyone so it wasnt the wrong relay).... so obviously he did some hack hard wire job to keep it running non stop.

im gonna poke around tomorrow after to stops snowing and see if i can find some of the butcher work.

ill get the battery load tested and im going to change the main cable.

what im thinking is the check valve went on the truck so the PO rewired to keep constant fuel pumping...

what do you think?

 

[bigalpha]

I'd say there is definitely some hack wiring going on. I don't know about the check valve or what, though.

Take a look on the driver fender at the ballast and see if he re-routed some wiring there.

 

[DaveVmax]

ok i found this on my fuel pump relay....

now why do you think the PO did that?

 

[bigalpha]

Did you replace it and see if it fixes the fuel pump problem?

 

[DaveVmax]

im just about to right now...

ill let you know

 

[bigalpha]

Good luck.